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  SE01-D5-PM2-P-013 (SE01-A002)
 
Reservoir Characterization at the “RR” Geothermal Field, West Java, Indonesia Shown by High Resolution Three-Dimensional Delay Time and Shear Wave Splitting Tomography
Rexha Verdhora RY#+, Tania MEIDIANA, Andri Dian NUGRAHA
Bandung Institute of Technology, Indonesia
#Corresponding author: rexha.vry@gmail.com +Presenter

Observation of micro-earthquakes induced by intensive geothermal exploitation at the “RR” geothermal field in West Java, Indonesia is used to detect the fracture and permeability zone. Using local monitoring seismometer network, tomographic inversions were conducted for the three-dimensional Vp, Vs, and Vp/Vs structures of the reservoir for January 2007 to December 2009. The parameterization model blocks used had dimension of 1 x 1 x 0.25 km3, so it can image velocity structure of reservoir with high resolution. Seismic tomographic inversions were conducted using delay time tomography, based on the differences of observed and calculated travel times. The travel times on the three-dimensional velocity model were calculated using ray tracing pseudo-bending method. We also conducted shear wave splitting (SWS) tomography to image subsurface anisotropy distribution. Our tomographic inversion results indicate the presence of low Vp, low Vs, and low Vp/Vs at depths of about 1 – 3 km below MSL. This features were interpreted as steam-saturated rock in the reservoir area of The “RR” geothermal field. The existences of the reservoir area are supported by the data of well-trajectory. Furthermore, SWS tomography results image high anisotropy located at our interested area and can be related to the fractures caused by injection well in the geothermal field. The exploitation and production of the geothermal field can cause changes in the reservoir phase system when the progressive depletion of pore fluid causes the replacement of pore fluid with paper. So, there is a possibility that the reservoir’s phase system may has changed to steam-saturated rock and build features of steam cap at the shallow zones.

  SE01-D5-PM2-P-014 (SE01-A003)
 
Seismic Structure of Crust and Uppermost Mantle Beneath Northern Vietnam and Its Tectonic Implications
Van-Duong NGUYEN#+
Academia Sinica, Taiwan
#Corresponding author: duongnv@igp-vast.vn +Presenter

Northern Vietnam is located in the southeasternmost extension of the Himalayan syntaxis, which is mechanically linked to the Tibetan plateau through the Red River fault. Obtaining knowledge on the crustal structure beneath northern Vietnam is a fundamental objective to understand the tectonic development in this region. The seismic data recorded from 25 broadband seismic stations over northern Vietnam from 2006 to 2012 provided a unique opportunity to study the deep structure and crustal deformation in this region. This report presents estimates of the crustal shear wave velocity structure beneath northern Vietnam, based on the linearized inversion of stacked receiver functions. The shear wave velocity structure in the northwestern region is relatively slow and more complex, whereas the velocity in the Red River Delta and northeastern region is slightly faster and simple. The areas of slow velocities in the crust possibly coincided with the observations of partial melting in the active regions, which may be related to the extension processes of the lithosphere or the rapid eastward flow of the deep crust. Those of faster velocities are consistent with the stable continent, suggesting small changes over the tectonic history in the processes that form the crust.

  SE01-D5-PM2-P-015 (SE01-A018)
 
S-Velocity Structure of the Crust and Uppermost Mantle of East Asia from Ambient Seismic Noise
Michael WITEK1#+, Shuoxian NING1, Tae-Seob KANG2, Suzan VAN DER LEE1, Sung-Joon CHANG3, Jieyuan NING4
1 Northwestern University, United States, 2 Pukyong National University, South Korea, 3 Kangwon National University, South Korea, 4 Peking University, China
#Corresponding author: mwitek2@gmail.com +Presenter

We have collected continuous vertical-component broadband data from 1109 seismic stations in regional networks across China, Korea, and Japan for the year 2011, and we have measured over half a million Rayleigh wave group velocity dispersion curves from one-year stacks of station-pair ambient seismic noise cross-correlations. The Rayleigh wave group velocity dispersion curves are regionalized on a tessellated spherical shell grid in the period range 10 to 50 s to produce maps of Rayleigh wave group velocity distributions. Maps at 10 seconds period match well with geologic features at the surface. In particular, we observe low group velocities in the Songliao, Bohai Bay, Sichuan, Ordos, Tarim, and Junggar Basins in China, and the Ulleung and Yamato Basins in the East Sea (Sea of Japan). Higher group velocities are observed in regions with less sediment cover. At periods around 30 s, we observe group velocity decreases going from east to west in China, representing an overall trend of crustal thickening due to the collision between the Indian and Eurasian plates. The Ordos and Sichuan blocks show higher group velocities relative to the eastern margin of the Tibetan Plateau, possibly reflecting low temperatures in these cratons. Using the Rayleigh wave group velocity distributions, we have performed 1D linear inversions at each node on the spherical shell grid to retrieve S-velocity perturbations with respect to the reference model LITHO1.0 of Pasyanos et al. (2014). This has allowed us to construct a 3D model of the crust and uppermost mantle for East Asia. We observe large-scale lateral variation in the crust compared to the LITHO1.0 model. From 50 to 100 km depth, we observe a low-velocity mantle wedge underneath Japan and the Strait of Korea, and at 100 km depth we see a general trend of increasing S-velocities from east to west, possibly reflecting temperature variations in the mantle.

  SE02-D5-PM2-P-012 (SE02-A003)
 
Triggering of Earthquake Swarms Following the 2011 Tohoku Megathrust Earthquake
Koji UMEDA#+, Koichi ASAMORI
Japan Atomic Energy Agency, Japan
#Corresponding author: umeda.koji@jaea.go.jp +Presenter

Earthquake swarms, often interpreted to result from fluids invading the brittle seismogenic zone, have seismicity patterns that are significantly different from an aftershock sequence. Following the Mw 9.0 Tohoku-Oki earthquake, an unusual, shallow normal-faulting swarm sequence occurred near the Pacific coast in the southeastern Tohoku district. An integrated approach combining geophysical and geochemical methods was utilized to identify the presence of aqueous fluids around the seismic source region and their derivation. Magnetotelluric inversion defined an anomalous conductor with a width of 20 km clearly visible to depths of more than 20 km, extending to the base of the crust. Independent geophysical observations, including seismic, strongly support the suggestion that fluid-filled porous materials and fluids associated with slab dehydration reside in the convergent plate boundary. In order to provide geochemical constraints on the source of the fluids triggering the swarm activity, new helium isotope data were acquired from gas and water samples around the seismic source region. The observed 3He/4He ratios in these samples are significantly lower than the atmospheric value of 1.4E-6, indicating that mantle helium contributed less than 10% of the total helium. Plausible sources of the fluids can be attributed to waters produced by isothermal decompression of metamorphosed accretionary prism sediments accompanying uplift and exhumation, rather than dehydration reactions in the subducted oceanic crust and/or hydrated mantle below the fore-arc mantle wedge. Owing to the continuing dehydration of metamorphosed rocks at depths of around 20 km, the fluids migrate into the seismic source region. The swarm sequence would have been triggered by stress changes associated with the Tohoku-Oki earthquake, enhanced by vertical metamorphic fluid expulsion from the reaction zone.

  SE02-D5-PM2-P-013 (SE02-A009)
 
Estimation of the Strong Ground Motion and Intensity Distribution of the 2014 Ms7.3, Yutian Earthquake, Xinjiang, China
Haixia SHI1#+, Ke SUN2, Lingyuan MENG1
1 China Earthquake Networks Center, China, 2 Institute of Earthquake Science, China Earthquake Administration (CEA), China
#Corresponding author: shihaixia08@seis.ac.cn +Presenter

The February 12, 2014, MS7.3, Yutian earthquake of Xinjing Province, China, occurred as a result of shallow strike-slip faulting in the tectonically complex region of the northern Tibetan Plateau, with focal depth of 17 km. This earthquake occurred several hundred kilometers north of the convergent India-Eurasia Plate boundary. The location of Yutian earthquake is 110 km north of Yutian city, Hetian district. The maximum intensity is up to IX in the near-fault field shown in the ShakeMap from the China Earthquake Administration (CEA), which is different from the result from USGS. In this study, we analyzed the source mechanism and studied the effect of slip distribution on the fault plane. One finite fault source model was constructed and the strong ground motion, including acceleration and velocity, were calculated. Based on the simulation of the near-fault strong ground motion, we described the Intensity distribution of the Yutian earthquake. The maximum simulated Intensity, which is IX, is consistence with the results of the CEA, but larger than that from USGS’s VII. In fact, the numerical modeling developed in this study has great application in the strong ground motion prediction and Intensity estimation for the earthquake rescue purpose.

This work is financially supported by the Natural Science Foundation of China (Grant No. 41204038), by Science for Earthquake Resilience of CEA (XH14055Y), and by China Earthquake Administration earthquake tracking project (2015010103).

  SE02-D5-PM2-P-014 (SE02-A010)
 
Source Parameters of the 2013, MW 7.7, Pakistan Earthquake and the Estimation of the Intensity Distribution
Fengfan ZHAO#+, Haixia SHI
China Earthquake Networks Center, China
#Corresponding author: zhaoff@seis.ac.cn +Presenter

The September 24, 2013, MW 7.7, earthquake occurred in south-central Pakistan as the result of strike-slip at the shallow crustal depths, 25km. This event occurred within the transition zone between northward subduction of the Arabia plate beneath the Eurasia plate and northward collision of the India plate with the Eurasia plate. The location of Pakistan earthquake is 69km north of Awaran, Pakistan. The maximum intensity is up to IX in the near-fault field shown in the ShakeMap of the USGS. In this study, we analyzed the dynamic source process with the source mechanism and empirical relationships, selected the effect of slip distribution on the fault plane based on two models. One finite fault source model was constructed and we calculate the strong ground motion including acceleration and velocity. Based on the simulated results of the near-fault strong ground motion, described the Intensity distribution of the Pakistan earthquake field. The simulated Intensity indicated that, the maximum Intensity value is IX, and region with and above VII is consistence with the ShakeMap of USGS. In fact, the numerical modeling developed in this study has great application in the strong ground motion prediction and Intensity estimation for the earthquake rescue purpose.

This work is financially supported by the Natural Science Foundation of China (Grant No. 41404045) and by Science for Earthquake Resilience of CEA (XH14055Y).

  SE02-D5-PM2-P-015 (SE02-A012)
 
Three-Dimensional Plate Geometry and Velocity Model for the Nankai Trough Subduction Seismogenic Zone Based on Structural Studies
Ayako NAKANISHI1#+, Narumi TAKAHASHI1, Yojiro YAMAMOTO1, Tsutomu TAKAHASHI1, Seckin Ozgur CITAK1, Takeshi NAKAMURA1, Koichiro OBANA1, Shuichi KODAIRA1, Yoshiyuki KANEDA2
1 Japan Agency for Marine-Earth Science and Technology, Japan, 2 Nagoya University, Japan
#Corresponding author: ann@jamstec.go.jp +Presenter

Not only to estimate precise coseismic rupture area of the Nankai megathrust earthquake but also to predict seismic and tsunami hazard, it is necessary to make more realistic three-dimensional plate and velocity structure models of the entire Nankai Trough seismogenic zone. Although various three-dimensional plate models for the Nankai Trough has been used or proposed in each numerical calculation study, it is important to provide the most realistic and reliable three-dimensional geometry of the subducting plate as the standard plate model for consistent evaluation on each study. We present a three-dimensional plate and structure models of the Nankai Trough subduction seismogenic zone, based on results from a wide-angle ocean bottom seismographic (OBS) surveys. Our plate and structure model of the coseismic slip area show the first time the visible, reliable and realistic three-dimensional model. The reliability of the three-dimensional plate model and three-dimensional seismic velocity model is confirmed by comparing theoretical first arrivals calculated from two-dimensional structure models sampled from the three-dimensional model along seismic profiles with observed traveltime data.  Spatial validity of the three-dimensional model  is also confirmed by sufficiently small difference in hypo central parameters determined from previously published result of seismic tomography and our three-dimensional structure model in the Hyuga-nada region; latitude and longitude within ±0.1° and depth within ~±5km. We therefore conclude that such an extent or degree of difference in hypocentral parameters will have an effect on results of numerical simulation study in which our three-dimensional models are used.

  SE02-D5-PM2-P-016 (SE02-A014)
 
The Variation of Late-Cenozoic Vertical Activity of the Beichuan-Yingxiu Fault and the Jiangyou-Guanxian Fault at Central Longmenshan Range and Their Tectonic Implications
Xibin TAN1#+, Xiwei XU2
1 Institute of Geology, China Earthquake Administration, China, 2 China Earthquake Administration, China
#Corresponding author: tanxibin@sina.com +Presenter

The Longmenshan Mountain on the eastern Tibet plateau possesses the deepest topographic gradient on the margins of the plateau. Along the Longmenshan Mountain, there are several parallel northwest-trending thrusts, which are collectively referred to as the Longmenshan Thrust Belt (LTB). The Longmenshan Mountain is one of the key areas for the research on the uplift history and uplift mechanism of the plateau, and predecessors had done several researches on the exhumation history using the thermochronology methods. Based on the predecessors’ thermochronology researches, we add some samples at the middle segments of the LTB, and get 6 Zircon Fission Track (ZFT) data and 6 Apatite Fission Track (AFT) data. The research reveals that the vertical activities of the Central fault and the Range-frontal fault since 8 Ma are much different separated by the Xiaoyudong fault: north to the Xiaoyudong fault, the average vertical slip rate along the Central fault and the Range-frontal fault is about 0.1 mm/yr and about 0.55 mm/yr, respectively; south to the Xiaoyudong fault, the average vertical slip rate along the Central fault and Range-frontal fault is about 0.55 mm/yr and about 0.1 mm/yr, respectively. The late-Cenozoic vertical slip rate of the faults revealed by the thermochronology data is coincided with the co-seismic vertical displacement of the Wenchuan earthquake. The horizontal shortening across the Range-frontal fault (north to the Xiaoyudong fault) reaches 8-12 km since 8 Ma, which indicates that the crustal shortening performing as the thrust movement along the main faults is the one of the main causes for the uplift and exhumation of the Longmenshan Mountain.

  SE02-D5-PM2-P-017 (SE02-A016)
 
High Precision Hypocenter Relocation from Teleseismic Double-Difference Relocation Method in the Indonesian Region Using a 3D Seismic Velocity Model
Andri Dian NUGRAHA1#+, Hasbi Ash SHIDDIQI1, Sri WIDIYANTORO1, Mohamad RAMDHAN2
1 Bandung Institute of Technology, Indonesia, 2 Agency for Meteorology, Climatology, and Geophysics (BMKG), Indonesia
#Corresponding author: andridn104@gmail.com +Presenter

We compiled and relocated about 32,000 earthquakes events around Indonesia region that reported by Indonesian Meteorology, Climatology, and Geophysics Agency (MCGA) from April 2009 to January 2015. We performed relocation inversion utilizing local, regional and teleseismic arrival time data. Our previous study of 3D seismic velocity model beneath the Indonesian region with grid size 1o by 1o and the 1D seismic velocity model were used for the regions inside and outside Indonesia region, respectively. This method improved limitation from MCGA earthquake data catalog in which events were recorded from scattered seismic station array and insufficient azimuthal gap around Indonesia. Our results show that travel-time RMS residuals were greatly reduced compared to those of the MCGA catalog. Seismicity at shallower depth (less than 50 km) shows significant improvement, refining shallow geological structures, e.g. trench and major strike slip faults. Clustered seismicity is also detected beneath volcanic regions, and probably related to volcano activities and also major faults nearby. In the Sunda arc region, seismicity at shallower depths is centered at two major zones parallel to the trench strike direction, i.e. around fore-arc and in the main land that can be related to major faults, e.g. The Great Sumatran Fault, and volcanic fronts. Below the Java island region, relocated hypocenters depict a double seismic zone pattern. A seismic gap is detected in the Sunda-Banda transition zone, where the transition from oceanic to continental crust of the Indo-Australian plate exists. In eastern Indonesia, shallow earthquakes are related to major strike slip faults, e.g. Sorong and Palu-Koro faults, volcanism activities, and shallow part of subduction and collision zones. We also compare our result for the Sunda arc region with slab 1.0 model and the relocated events show good agreement with the slab geometry. Horizontal position shifts of relocated catalog events are mostly perpendicular to the trench direction. These shift directions may be influenced by velocity anomalies of the subducted slabs that did not exist in the processing of the previous catalog.

  SE02-D5-PM2-P-018 (SE02-A023)
 
Active Tectonic of Zanjan Depression, Western Alborz, Iran and its Seismic Potential Behavior
Abdollah SAEIDI#+
CGMW for the Middle East, Iran
#Corresponding author: abdollahsaidi@yahoo.fr +Presenter

The Zanjan depression has formed in the Late Miocene during the shortening of Alborz an Central Iran crust. Thick sediments of Late Miocene marl and Plio – Pleistocene alluvium has been accumulated in this young basin with its high rate subsidence in Pliocene and Pleistocene. This basin is surrounded by Paleogene – Neogene volcanic rocks of western Alborz in the North and Phanerozoic rocks Eocene volcano sedimentary deposits of Central Iran structural zone.

The compressional condition of Alborz crust has been continued up to now and caused some main active faults in Zanjan region northwest of Iran. The main faults, which played an important role in control of deformation of Zanjan basin rocks as well as the Quaternary deposits, are North Zanjan high angle reverse fault with a sinistral strike-slip component and Farsijin reverse fault with its recent dextral component. Between these two active faults, Farsijin fault is more important due to its activity and vicinity and to Zanjan city. The clock wise rotation of Alborz Mountains in north of Zanjan occurred along this north-south trending fault with a five kilometers right lateral displacement . The Farsijin Fault in its termination is very close to Zanjan city and has cut and displaced the recent fluvial terraces of Zanjan fore-land basin. The earthquake focal mechanisms of previous seismic in this part of Alborz Mountains  indicate that this region has affected by several seismic activities.

According to our estimation on geometry and kinematic characteristics and length of Farsijin fault, it may cause an earthquake around 6.8 Mw. Undoubtly the future activity of this fault would be serious threat for Zanjan city and its 1.2 million populatin.

  SE04-D5-PM2-P-007 (SE04-A003)
 
Character of Chemical and He-Ne Isotope Compositions in the Central South Area of Liaoning, NE China
Zhihua ZHOU1#+, Ying LI2, Haiyan WANG3
1 China Earthquake Networks Center, China, 2 Institute of Earthquake Science, China Earthquake Administration (CEA), China, 3 Earthquake Administration of Liaoning Province, China
#Corresponding author: basalin@hotmail.com +Presenter

Chemical and He-Ne isotope compositions have been measured in gas and water samples for 12 wells and springs in the central and southern Liaoning in September 2014. The temperature for all samples varied from 7.2 to 66℃. Based on their major constituent anions (HCO3- and SO42-) and cations (Ca2+ and Na+), most of measured water samples display a compositional spectrum among three types: NaCa-SO4HCO3, Na-HCO3(SO4) and Ca(Na)-SO4(HCO3) water chemistry types, with the exception of one sample from Jinzhou near the Liaodong Peninsula, which belongs to Ca-Cl water-type. Most of the water chemistry types controlled by water-rock processed which fluids circulated through and equilibrate with the crust, such as mineral dissolution, diffusive exchanged, and the input of deep fluid. The observed 3He/4He ratios from 0.24Ra to 0.44Ra indicate 3.35-7% helium from mantle, 92.83- 96.48% from crust and about 0.17% from atmosphere. The 3He/4He results require a certain content of helium from the mantle, but the main reason for the observed values should be it was diluted by addition of radiogenic helium produced in the crust or during the fluid deep circulations. The 3He/4He ratio for PLD sample is the largest which is sampled near the NE-trending Jinzhou fault. The other lower 3He/4He ratios are similar with the similar distance on both sides of the Jinzhou fault. The active faults play an important role in the altitude of 3He/4He ratios, which means it was the main channel in transferring mantle components to the surface in the non-volcanic regions.

This work is financially supported by the Natural Science Foundation of China (Grant No. 41273073), by Science for Earthquake Resilience (XH15011), and by China Earthquake Administration earthquake tracking project (2015010304).

  SE04-D5-PM2-P-008 (SE04-A004)
 
Anomalies of Total Column CO Related to MS³5.5 Earthquakes in Southern Xinjiang, China During 2011 to 2014
Yueju CUI#+, Jianguo DU
China Earthquake Administration, China
#Corresponding author: cehuicuiyueju@126.com +Presenter

With the development of multi-parameter remote sensing technology, the anomalous variations of some gaseous components in the atmosphere, which can be retrieved with the hyper-spectral remote data, are considered as new information for the earthquake processes. The best results of geological survey and earthquake monitoring can be obtained by using the remote sensing technique in Xinjiang because of the poor vegetation there. Therefore, the anomalies of CO concentration during preparation and occurrence of 10 MS³5.5 earthquakes in Xinjiang Uygur Autonomous Region (Xinjiang) were investigated in the view of seismogeology, geomorphology and meteorology. Total column CO (TotCO) variations associated with the earthquakes in the difference geomorphic regions in Xinjiang, China from January 2011 to June 2014 were obtained using the satellite hyper-spectrum data. TotCO anomalies occurred in the epicenter areas and vicinity with 8 earthquakes of the nine studied earthquakes. The anomalies were characterized by changing annual cycle of variation, abnormal deviations from the fitting line, such as evident increase, sharp drop, which depended on the tectonic and geographic features. The anomalies of gas concentration related to the earthquake developing can be mainly attributed to gas emission from the lithosphere and to the physical and plasma-chemical reactions in the atmosphere known as Lithosphere-Atmosphere-Ionosphere coupling (LAIC). The results indicate that the high-spectrum remote sensing technique is potential for us to monitor the gas-geochemical variations associated with earthquake especially in the arid area.

  SE04-D5-PM2-P-009 (SE04-A007)
 
Investigation of the Records of Earthquake Slip in Carbonaceous Materials from the Taiwan Chelungpu Fault by Means of Infrared and Raman Spectroscopies
Tetsuro HIRONO#+
Osaka University, Japan
#Corresponding author: hirono@ess.sci.osaka-u.ac.jp +Presenter

To understand the mechanism of fault lubrication during the 1999 Taiwan Chi-Chi earthquake, we developed a new temperature proxy for carbonaceous materials by using infrared and Raman spectroscopies together with heating and friction experiments. We found marked anomalies in the infrared and Raman spectra of carbonaceous materials retrieved from the primary slip zone of the earthquake: the infrared spectra exhibited very weak aliphatic CH2 and CH3 peaks and aromatic C=C absorbance peaks, and the Raman spectra exhibited very weak disordered and graphitic bands and a high ratio of disordered band area to graphitic band area. Those weak peaks and bands and the band area ratio were reproduced by heating carbonaceous materials from the nearby host rock to 700 °C. These results suggest that the frictional heat in the slip zone reached approximately 700 °C. We characterized the host rock’s carbonaceous materials by means of elemental analysis, pyrolysis–gas chromatography–mass spectrometry, and simultaneous thermogravimetry–differential scanning calorimetry and found that the H/C and O/C ratios were 0.108 and 0.400, respectively (which are close to the ratios for lignin) and that the volatile fraction was as high as 48 wt %. The pyrolysates obtained by heating from 100 to 400 °C were dominated by phenols, fatty alcohols, and n-alkanes. When the residue from pyrolysis at 100–400 °C was rapidly heated to 700 °C, the resulting pyrolysate was dominated by phenols, aromatic compounds, heterocyclic compounds, and n-alkenes. This information suggests that changes in the infrared and Raman spectra with increasing temperature may have been due to decomposition and aromatization reactions during pyrolysis. Rapid heating during earthquake slip may promote reactions of carbonaceous materials that are different from the reactions that occur during long-term metamorphism.

  SE04-D5-PM2-P-010 (SE04-A009)
 
Effect of Seasonal Hydrological Loading Over Indian Sub-Continent and Himalaya from GPS and GRACE Observations
Ajish P SAJI1#+, P.S. SUNIL1, C.D. REDDY1, Param K R GAUTAM2
1 Indian Institute of Geomagnetism, India, 2 Wadia Institute of Himalayan Geology, India
#Corresponding author: ajishpsaji@gmail.com +Presenter

Due to the advancement of space geodetic techniques and its accuracy, it is established that, apart from the tectonic motions on the Earth’s surface, deformations are also caused due to Earth tides, tidal and non-tidal ocean height changes, atmospheric and hydrological surface loading.  Since space geodetic techniques like VLBI, GPS, InSAR, SLR etc., are used to measure the Earth's surface motion, the effects are resulted as changes of co-ordinates in terrestrial reference frame and are usually taken care during the data analysis except hydrological loading. Regions like Indian subcontinent and Himalayas, monsoon rain fall causes a large amount of seasonal hydrological variation effects on crustal surface.

To study this seasonal hydrological mass cycle and its loading effects, data from 27 permanent GPS stations spread across the Indian sub-continent and 42 stations spread across Nepal Himalaya were utilized for the study. Along with GPS data, we use spherical harmonic coefficients of the Earth's gravity field estimated from GRACE data to model the elastic displacements due to the changing load. Hydrological loading which is a seasonal signal can be traced out from both GRACE as well as GPS data. Vertical deformation from GRACE data is well correlated with GPS signals in terms of seasonal signals. Subtraction of GRACE derived vertical displacements from GPS observed time series will separate out tectonic effects from hydrological effects which is of interest for deformation study. The seasonal signals obtained from GPS and GRACE are compared and analyzed for the periodic monsoonal effects in the region. The behavior of seasonal deformations before and after monsoon is correlated. The WRMS reduction in GPS vertical rate due to reduced GRACE derived vertical displacement essentially compares the consistency between GPS and GRACE measurements. The spatial variation of correlation between GPS and GRACE over the continent due to hydrological effect and its contribution in terms of crustal deformation pattern over India and Nepal are explained.

  SE04-D5-PM2-P-011 (SE04-A010)
 
Permeability of Fault Zones Determined by Hydraulic Tests and Continuous Groundwater-Level Observation
Norio MATSUMOTO, Norio SHIGEMATSU, Naoji KOIZUMI#+
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Japan
#Corresponding author: koizumi-n@aist.go.jp +Presenter

GSJ, AIST constructed an integrated groundwater observatory at Matsusaka-Iitaka as a part of the groundwater and crustal deformation observation network for the prediction research of the Nankai and Tonankai earthquakes (Shigematsu et al., 2012; Koizumi, 2013). Hole 1 (total depth 600m) was penetrated the Median Tectonic Line (MTL) at a depth of 473.9 m. Total depth of Hole 2 is 208 m. We obtained core samples and well logging data and conducted hydraulic tests in these wells. Screened depth of Hole 1 is 547.6-558.5m and is located in the lower fracture zone of the MTL fault zone developed in the Sanbagawa metamorphic rocks. Screened depth of Hole 2 is 145.5-156.4 m and is located at a branch fault in the Ryoke Granitolds (Shigematsu et al., 2012).  The results of the hydraulic tests and continuous groundwater observation show 1.8-8.5 x 10-16 and 1.8 x 10-15 m2 in Hole 1 and Hole 2, respectively. These permeabilities are consistent with laboratory permeability measurement of MTL fault rocks (Wibberley and Shimamoto, 2003).

  SE05-D5-PM2-P-004 (SE05-A002)
 
Deep-Tow Magnetic Survey of Fonualei Rift and Spreading Center (FRSC) at 16〫35'S in the Northeastern Lau Basin
Chang Hwan KIM#+, Myoung Hoon LEE, Chan Hong PARK, Hyeon Yeong PARK
Korea Institute of Ocean Science & Technology, South Korea
#Corresponding author: kimch@kiost.ac +Presenter

Fonualei Rift and Spreading Center (FRSC) are located in the northeastern part of the Lau Basin which is the active back-arc basin. Deep-tow magnetic surveys have been carried out in FRSC. In deep-tow magnetic survey, to compensate for influence of uneven distance between bathymetry and sensor height, magnetic anomaly was continued upward to a level plane. We calculated crustal magnetization by using inversion method, and tried to find the hydrothermal vent and understand the structure of ocean floor crust. The result of deep-tow magnetic survey at FRSC shows that Central Anomaly Magnetization High (CAMH) records the max value which is associated with active ridge. The direction of SSW-NNE of CAMH corresponds with the direction of the principal spreading ridge in the Lau Basin. The low crustal magnetization of about 0 A/m is supposed to correlate with submarine hydrothermal vent.

  SE05-D5-PM2-P-005 (SE05-A003)
 
Seismic Reflection Data Reveal the Characteristics of Magmatic Activity in the South China Sea
Xiaoxiao SONG#+, Chun-Feng LI
Tongji University, China
#Corresponding author: xiao1326836@163.com +Presenter

This study identifies various igneous features, such as stocks, laccoliths, sills, volcanos, and volcanic edifices based primarily on multi-channel seismic reflection data from the South China Sea (SCS) region. They are often characterized by high positive-amplitude reflections, and by chaotic or blank reflections beneath because of its seismic shielding effect. The relationship between the igneous rocks and the surrounding sediments is also evident from the upturning of the host rocks and the domal uplift of the over-burden. Sills of different shapes are encountered in the study area and always co-occur with other igneous features and faults, which probably behave as magma source and passage for sills, respectively. The igneous features, except sills, show obvious positive gravity and magnetic anomalies. We estimate the timing of igneous activities using seismic stratigraphic relationship and analyze their distribution in the SCS region, and discover that the igneous emplacements during rifting and seafloor spreading phase are sparse in the margins and adjacent areas of the SCS. This provides additional evidence for a magma-poor northern margin of the SCS. The limited magmatic activity occurred mostly after the cessation of seafloor spreading in the continental slope area, maybe influenced by extension in relation to cooling and subsidence of the SCS.

  SE05-D5-PM2-P-006 (SE05-A007)
 
Comparison of FTIR and XRD Characterization of Hydrothermal Alteration Mineralogy: Constraints from the Co-O Orebody, Agusan del Sur, Philippines
Sofia Marah FRIAS#+, Mervin Dave VIRREY, Jamela Jirah CLEMENTE, Ruth Esther DELINA, Marc Jefferson PADILLA, Carlo SALAC, Carlo ARCILLA
University of the Philippines Diliman, Philippines
#Corresponding author: sofiamarahfrias@gmail.com +Presenter

The use of portable infrared spectrometer in geologic alteration mapping is one of the most common techniques used in gold and copper ore exploration. Phyllosilicates, primarily the clay mineral groups derived from hydrothermal alteration, are characterized through the presence of hydroxyl groups in its crystal structure. The superimposition of various clay species and their overlapping spectra, however, present difficulties in correctly identifying minerals if only FTIR data are obtained.  In order to obtain comparative certainty, thirty four samples from an epithermal gold deposit in Agusan del Sur, Philippines were analyzed for clay mineral characterization using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). About 0.1 mg to 10 mg of heated sample and 100 mg of heated KBr were pulverized, mixed, pressed into a thin film and analyzed using FTIR. Furthermore, the samples were analyzed using X-ray diffraction to obtain the full clay species characterization. Based from the FTIR results, all of the samples showed defined peaks at 1000cm -1 to 500 cm-1 which may account for illite or quartz, while at 450 cm-1 and 1000 cm-1 dickite and quartz share the same peaks. Moreover, clay minerals like dickite and illite also share the same peaks at 1000 cm-1 and 500 cm-1. All samples peaking at 3,500-3,400 cm-1 may be attributed to the hydroxyl bond. However, most of the silicates like alunite, halloysite, kaolinite, pyrophyllite, boehmite, tremolite, smectite, were identified by XRD were not detected by FTIR, along with sulfides like arsenopyrite and  pyrite, and oxides such as hematite. These results suggest that FTIR results may be equivocal in identifying key clay alteration minerals and may need independent identification by XRD methods to fully delineate different clay mineral assemblages.

  SE05-D5-PM2-P-007 (SE05-A008)
 
Mineralogy and Geochemistry of Garnierites from Southern Palawan Ni-Laterite Deposits, Philippines
Ma. Isabella HERMO#+, Lizalyn Giezelle CADELINA, John Paul DE JESUS, Ian ESPALDON, Paolo Andre BENAVIDES, Russel Raffy ONG, Carmela Alen TUPAZ, Fe Corazon LORETO, Carlo ARCILLA
University of the Philippines Diliman, Philippines
#Corresponding author: belay.hermo@gmail.com +Presenter

Garnierites are green, highly nickel-enriched silicate ores hosted in weathered ultramafic rocks. This study presents the mineralogical and geochemical data of garnierite samples obtained from the ophiolitic suite in Mt. Bulanjao, Rio Tuba and Berong, Quezon, Southern Palawan, Philippines. The collected garnierites occurred as: (a) 2-20 mm veins in consolidated saprolitic rock; (b) soft surface encrustations; and (c) thin “booklets” layered with thin chalcedony sheets. The mineralogy and geochemistry of selected samples were investigated using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), and Fourier Transform Infrared (FTIR) spectroscopy. XRD and XRF analyses reveal that the samples could be divided into to three groups according to their dominant nickel-bearing mineral: amorphous silica, serpentine, and talc-serpentine. XRD analyses show that vitreous samples, exhibiting broad peaks (~4Å) characteristic of amorphous silica, had only 1-10% nickel content. Earthy and friable samples, showing ~7Å peaks characteristic of serpentine minerals, had nickel content ranging from 10-50%. These serpentine minerals were identified to be lizardite, chrysotile, antigorite, and nepouite. The third group comprises morphologically-similar samples to the latter group but shows both ~7Å and ~10Å peaks, characteristic of serpentine and talc, respectively. FTIR analysis revealed three spectral regions complementing the XRD results: O-H stretch absorption bands at 3400cm-1-3500cm-1, Si-O-Si stretch absorption bands at 1000cm-1-1150cm-1, O-H bending absorption bands at 650cm-1-700cm-1 and Si-O-Si bending absorption bands at 460cm-1-480cm-1. These characterization data will be useful for beneficiation studies to recover Nickel and other elements (e.g., Sc) from the laterite ores.

  SE05-D5-PM2-P-008 (SE05-A009)
 
Comparative Chemical Analytical Methods of Nickel Laterite Samples from the Philippines
Ramjay Jude BOTOR#+, Jayvee ANGELES, Clemente CAJIGAL, Jayson Gabriel PINZA, Paolo Andre BENAVIDES, Carmela Alen TUPAZ, Carlo ARCILLA
University of the Philippines Diliman, Philippines
#Corresponding author: rjlbotor@gmail.com +Presenter

The Philippines is one of the largest sources of nickel in the world, derived mostly from laterite deposits weathered from ultramafic rocks. Due to the high water content of these ores, analytical results from various methods have often been discordant. In this study, samples were analyzed in nickel laterite mines of Rio Tuba Nickel Mining Corporation in Southern Palawan, Philippines. Results from pressed pellet and fused bead analyses using X-Ray Fluorescence (XRF) were then compared. Certified Reference Materials (CRM) acquired from Ore Research & Exploration Pty Ltd. (ORE) and laboratory internal standards were utilized for calibration of the XRF. The results impact the current accepted modes of analyses for nickel laterites used in direct shipping ores.

  SE05-D5-PM2-P-009 (SE05-A010)
 
Ultramafic Weathering and Laterization: Reactive Transport Geochemical Modelling of a Philippine Iron-Nickel Laterite
Karmina AQUINO#+, Emmanuel CODILLO, Carlo ARCILLA
University of the Philippines Diliman, Philippines
#Corresponding author: karminaaquino@gmail.com +Presenter

Ultramafic rocks in tropical areas such as the Philippines typically consist of heavily serpentinized peridotites and pyroxenites overlain by Ni-rich laterites. Ni-laterite is a residual type deposit characterized by preferential enrichment and depletion of certain immobile and mobile elements, respectively, during the weathering of ultramafic rocks.

Using GWB, a geochemical model of laterization process is presented to simulate the behaviour of certain minerals comprising the different zones in a typical laterite profile: limonite, saprolite and bedrock. In the model, a hypothetical 5m-thick lherzolite with predefined properties (i.e. porosity, dispersivity) was reacted with ultramafic-draining river water in a span of 130 years. Chrysotile, talc, clinochlore, hematite, goethite, magnetite, tremolite and quartz were allowed to precipitate in the system. The changes in the mineral saturation states of these minerals were evaluated and correlated with actual laterite mineralogy.

Goethite, which at the early stages of the process is undersaturated, shows gradual but persistent increase in saturation towards the end of the simulation. Hematite, which is initially undersaturated, rapidly becomes supersaturated at very shallow depths. Talc is initially undersaturated at the topmost layers and becomes more saturated with depth. Temporally, the depth of talc saturation migrates downward. Silica phases are static through time while calcite, chrysotile, clinochlore, magnetite, tremolite, cristobalite, gibbsite remains undersaturated throughout the simulation.

The modeling broadly replicates the typical zonation within a laterite profile consisting of an uppermost limonite layer rich in Fe-hydroxides and oxyhydroxides and a middle saprolite layer rich in hydrated Mg silicates represented here by talc. The temporal downward migration of talc results in the thickening of the limonite layer. The enrichment of Nickel in garnierites might be related to this talc migration. Not surprisingly, serpentine and chlorite remained undersaturated, implying that the abundance of these minerals is not due to weathering but probably to emplacement history.

  SE05-D5-PM2-P-010 (SE05-A012)
 
Comparative Geochemical Analytical Investigation of Scandium in Philippine Laterite deposits
Carmela Alen TUPAZ, Carlo ARCILLA#+
University of the Philippines Diliman, Philippines
#Corresponding author: caloy.arcilla@gmail.com +Presenter

The Philippines is one of the world’s largest nickel sources from its weathered ultramafic laterites. However most of the ore is shipped directly without processing. Recent findings (e.g., Kanematsu et al., 2011; Santos et al, 2014) suggest that Scandium could also be enriched in laterites but there is a dearth of Sc data from Philippine samples. To address the analytical gap, we conducted comparative chemical analyses for Sc using ICPMS and MPAES using certified standards. Initial results show that Sc is present in ppm levels in the laterite and, similar to other findings, is positively correlated with Fe. The significance for Philippine economic geology is that the low-grade, unmined iron-rich but nickel-poor laterites may actually host significant Sc that could add to the economic viability of these ores. Additionally, knowledge of Sc residence is an added step for local processing of laterite ores.

  SE05-D5-PM2-P-011 (SE05-A013)
 
Mobility of Major and Minor Elements in Nickel Laterites from Palawan, Philippines
Jeffrey BERMIDO#+, Cleodette LAGATA, Regino Alex CARRANZA, Lemuel MANGAHAS, Carlo ARCILLA, Russel Raffy ONG
University of the Philippines Diliman, Philippines
#Corresponding author: jeffreybermido@yahoo.com +Presenter

The tropical setting in the Philippines enhances the rate of chemical weathering in which ultramafic rocks undergo residual alteration to laterites. Limonite and saprolite layers from four laterite profiles in Southern Palawan Ophiolite were analyzed to determine the mobility of nine major and minor elements (Ni, Mg, Fe, Ca, Si, Mn, Cr, Al and Ti). The coefficient of mobility (τ) was determined by comparing the concentrations of weathered products with the original serpentinized peridotite material. Elemental compositions were obtained using Microwave Plasma – Atomic Emission Spectroscopy and X-ray fluorescence. Petrographic analyses showed that the bedrock comprises dunites and harzburgites that have undergone significant alteration to lizardite. X-ray diffraction characterized the limonite with iron oxyhdroxides goethite and hematite, while the saprolite was identified to be of goethite, hematite, lizardite, chromite, saponite, nontronite and magnetite. Results suggest that saprolitization favors the mobility of Mg and Si (τ= -0.87 to -0.99) with values indicating almost total removal due to weathering. Al, Fe, Cr and Mn are found to be relatively immobile and increase in abundance during the process. In limonitization, the mobile elements are Si, Ca and Mg (τ= -0.79 to -0.99). Nickel values follow (τ= -0.80 – 0.99) and Al, Fe, Cr and Fe show relative lower mobility. Fe is found to be most enriched in the limonite with τ=+2.69. In both processes, Ni and Ca show complex geochemical behavior while Ti show consistent immobility. Variation diagrams also show increasing trend with depth for mobile elements Mg and Si. These diagrams also show the decreasing trend of Fe, Cr, Al and Mn and the complex geochemical behavior of Ni and Ca. The mobility of elements is essential in understanding the weathering behavior of laterites from bedrock to limonite.

  SE06-D5-PM2-P-022 (SE06-A001)
 
Lithospheric Shear Wave Velocity and Radial Anisotropy Beneath the Northern Part of North China from Surface Wave Dispersion Analysis
Yuanyuan FU#+
Institute of Earthquake Science, China Earthquake Administration, China
#Corresponding author: fuyuanies@163.com +Presenter

Rayleigh and Love wave phase velocities in the northern part of the North China are obtained from ambient noise tomography in the period range of 8 to 35 s and two plane wave earthquake tomography at periods of 20 to 100 s using data recorded at 222 broadband seismic stations from the temporary North China Seismic Array and permanent China Digital Seismic Array. The dispersion curves of Rayleigh and Love wave from 8 to 100 s are jointly inverted for the 3-D shear wave structure and radial anisotropy in the lithosphere to 140 km depth. Distinct seismic structure are observed from the Fenhe Graben and Taihang Mountain to North China Basin. Low velocity anomalies are largely imaged beneath the Lüliang Mountain, Fenhe Graben and Taihang Mountain while high velocity anomalies are present in the North China Basin from the lower crust to the depth of 140 km. The high velocity in the North China Basin is probably related to mafic intrusion and depleted mantle residual of Archean lithosphere associated with strong lithosphere extension. The prominent low velocity anomaly beneath the Fenhe Graben and Taihang Mountain may be related to the asthenosphere upwelling during the Mesozoic reactivation. Large positive anisotropy with Vsh > Vsv in Fenhe Graben, Taihang Mountain and North China Basin could indicate horizontal layering of intrusion and alignment of minerals in the lithospheric mantle, which also argue for vigorous extensional deformation.

  SE06-D5-PM2-P-023 (SE06-A003)
 
Probabilistic Assessment of Tephra Fallout Hazard at Changbaishan Volcano, Northeast China
Hongmei YU#+, Jiandong XU, Bo ZHAO
Institute of Geology, China Earthquake Administration, China
#Corresponding author: yuhongmei188@163.com +Presenter

Tephra fallout is an important type of hazard caused by volcanic eruption, and is also one of the main hazards at Changbaishan volcano, Northeast China. Numerical simulation is an effective approach to assess the dispersion of tephra fallout. According to the theory of dispersion model, we developed a simple and practical diffusion program that can be run on a personal computer. The input parameters for the simulation of tephra fallout from the Millennium Eruption of Changbaishan volcano, such as the size, density and shape of the tephra, the bulk volume and column height, the diffusion parameter P(z), wind direction and intensity, were obtained by field investigation and laboratory analysis. The simulated results in the intermediate scope when the parameter β > 0.3 are in good agreement with the results from measurement in situ, indicating that the model is reliable and the parameters used in the model are reasonable. We carried out more than 20,000 tephra fallout simulations using a statistical dataset of wind profiles which are obtained from China Meteorological Data Sharing Service System (CMDSSS). Tephra fallout hazard probability maps related to high- and low- magnitude eruption scenarios in Changbaishan volcano, are constructed for several tephra thickness thresholds, such as 70 cm, 20 cm, 10 cm and 1 cm. The results from this study can give support to the risk mitigation plans in Changbaishan area.

  SE06-D5-PM2-P-024 (SE06-A004)
 
Effects of Data Distribution on Inversion Results
Honglin JIN#+, Jinwei REN, Guangyu FU
Institute of Earthquake Science, China Earthquake Administration, China
#Corresponding author: jhl_1968@126.com +Presenter

GPS and INSAR can be used to monitor the co-/inter-seismic deformations. This provides us a lot of data for inversions. However, different fault models, data distributions or inversion methods used during the inversions usually lead to different results. Among them, the effects of the data distribution are very great. For example of 2011 Tohoku earthquake, most co-seismic deformation data are distributed in hanging side from epicenter 300 km away, only several seafloor deformation data are obtained near the epicenter. Whether including the near field data or not in inversion leaded to obvious different results. In this study, we analyzed the effects of data distribution on inversion results, and compared the inversed and given models.

For the effects of data distribution on inversion results, we first provided a rupture model as the true seismic rupture model, and forward calculated its co-seismic deformations. Next we obtained a different result by changing the distribution of the data in inversion. At last we compared the new one with the given model. We considered two kinds of fault model in this study. One is a thrust fault with low dip angle (~30°) plate. Another one is an inland vertical strike slip model. The thrust fault model is mainly used to discuss the effect of the data distribution on the handing wall or the footwall, or the one distributed in near field or far field. The vertical strike slip fault is mainly used to consider the influence of the data density. We got conclusions as follows: the far field data reflects the deep slipping while the near field data reflects the shallow one; the result inversed using the data of hanging side or foot wall is much different with each other; the data density affects the inversion results but varies depending on fault rupture size.

  SE06-D5-PM2-P-025 (SE06-A007)
 
The Seismotectonic Characteristics at Eastern Margin of the Tibetan Plateau
Zhaofan XU1#+, Shixu JIA2, Min ZHOU3, Yan LIU2, Yong QIU2
1 China Earthquake Administration, China, 2 Geophysical Exploration Center, China Earthquake Administration, China, 3 China University of Geosciences, China
#Corresponding author: xuzhaofan126@126.com +Presenter

The vast Tibetan Plateau, known as roof of the world and revolved around steep orogenic belt, has been still uplift rapidly today. Though its eastern margin is within the context of long-term uplift and eastward enlargement and was host to an unanticipated great thrust-faulting Wenchuan earthquake on May, 2008, the active faulting studies, seismicity and deformation measurements all show not typical of the most great devastating reverse faulting historic earthquakes commonly rupture gently dipping thrust faults which slip occurs rapidly. It has been aroused great interests about these unique geological features at eastern margin of the Tibetan Plateau. Based on the data collected from the temporary and permanent seismic stations in the eastern margin and its adjacent areas in recent several years, the aftershocks of Wenchuan earthquake are located accurately in terms of Deep Seismic Sounding experiment model and the seismic wave velocity structures are determined using both active and passive source seismic data. In generally, almost all aftershocks are scattered in a narrow vertical hypocenter body with 330km×30km×30km, the aspect ratio of which in horizontal is about 11:1, though there are some local linear focus distributions and quake clusters. The seismic wave velocity structures show very strong laterally variations and obviously contrast among the different tectonic blocks. The seismotetonic patterns and geological features seemly suggest that in the eastern margin of the Qinghai-Tibet Plateau, the vertical crustal movement and tectonic upwelling should be the controlling factors which are responsible for the steep eastern margin building.

This research was supported by the International Collaboration Program on Earthquake, Tsunami and Volcano in East Asia (ZRH2014-06) and the National Science Foundation of China (40974033)

  SE06-D5-PM2-P-026 (SE06-A008)
 
Exploration for the Tectonic Environment of Wenchuan Earthquake
Shixu JIA#+
Geophysical Exploration Center, China Earthquake Administration, China
#Corresponding author: jiasx111@sohu.com +Presenter

On the basis of a more perfect deep seismic sounding observation layout, the crustal velocity structures and tectonic deformation of the central Longmenshan were investigated, and also the velocity - density inversion were carried out. The relationship among the basin-and-range coupling and Longmenshan building mechanism with the tectonic enviroment of strong earthquake develoment and seismogenic tectonics at the central Longmenshan are discussed.

The results show that the differences of average velocity in upper, middle and lower crust are 0.06-0.18 km/s, 0.12-0.25 km/s and 0.40-0.60 km/s in Songpan-Ganzi Block, Longmenshan fold zone and Sichuan basin. The crustal media nature in Longmenshan has great variations from top to bottom , which reveals brittle-plastic transform in different depths; Based on the crust velocity structure model, the crustal density structure along the profile are obtained. The crust structure of the central Longmenshan shows a wide bottom and narrow top "lower velocity - high density medium channel" which thrust up from west to east.

Tibetan plateau crustal materials flow to the east continuously. Plastic or semiplastic rheological medium are obstracted by hard mid-lower crust of Sichuan Basin, and forced to thrust up in central Longmenshan folded zones, which cause the upper crust greatly uplift .The action of extrusion thrust from west to east and uprush of mid-lower crust causes a strong upheaval in upper crust, a series of brittle deformation structure such as crust slippage broken, interface hyperplasia, surface pushover overthrust and sharp uplift in the fault zone. The "going up" central Longmenshan formed on the west edge of Sichuan Basin. In the fold-orogenic zones, brittle-ductile transfer zone in mid-upper crust, especially the rupture regions in brittle layers are probably the deep tectonic environment in which strong earthquakes prepared and occurred.

The research was supported by the National Science Foundation of China (41474075)

  SE06-D5-PM2-P-027 (SE06-A013)
 
Did Earthquake Tsunami Occur Around China in History?
Feng SHI#+, Honglin HE
Institute of Geology, China Earthquake Administration, China
#Corresponding author: shifeng@ies.ac.cn +Presenter

There are many records about “sea-overflow” in Chinese ancient books, which didn’t prove are tsunami. Base on the tectonics of China sea and records in ancient books, there are always arguments about whether or not occurred tsunami around China. In this paper, base on the analysis about historical earthquakes and ancient books, associated with numerical simulation and field investigation, we deem that there no devastating tsunami occurred around China. But if huge earthquake occur on the Ryukyu trench, Okinawa trough and Manila trench, the tsunami maybe could reach China. The worst impacts on China mainland from possible tsunamis are from the Manila Trench.

  SE06-D5-PM2-P-028 (SE06-A014)
 
Study on the Earthquake Catalogue and the Seismicity of North China, Mongolia and Adjacent Areas
Guangyin XU#+
Institute of Geophysics, China Earthquake Administration, China
#Corresponding author: xugy1971@163.com +Presenter

Using the earthquake catalogue from China, Mongolia and the global catalogue, the uniform catalogue of North China, Mongolia and adjacent areas has been established for the seismic hazard analysis and seismic zoning map of Mongolia according to the following principles. 1) Earthquakes, which just exist in one catalogue, need to be verified further. If the earthquakes occurred in the country where the catalog comes from, then they will be adopted. If not, it should be checked with other more data. 2) The events that come from the three data sources have be checked and verified as followings. (1) The parameters of earthquakes that occurred in China will be taken from China catalog. (2)The parameters of earthquakes that occurred in Mongolia will be taken from Mongolia catalog. (3) The parameters of earthquakes that occurred in the adjacent areas will be taken from the global catalog by Song et al.

According to the uniform catalogue, the seismicity of the North China, Mongolia and adjacent areas is analyzed, and the conclusions as followings are made. 1) The epicenter map can be roughly divided into two parts, bounded by the longitude line 105°E , in accordance with the “North-South Seismic Belt” of China. The seismicity is in a high level with many strong earthquakes in the west and is in a low level with little strong events in the east. 2) Most earthquakes are shallow-focus events, but there are also several middle or deep-focus events in the study area. 3) Earthquakes with magnitude more than 5 are basically complete since 1450 A.D., and the seismicity of the study areas is in a high level since 1700 A.

  SE06-D5-PM2-P-029 (SE06-A016)
 
Research on Ratio of Maximum Considered and Design Basis Earthquakes in China
Kun CHEN#+, Mengtan GAO
Institute of Geophysics, China Earthquake Administration, China
#Corresponding author: chenkun-6620@163.com +Presenter

Seismic zonation map is essential for carrying out safe and economic design of general construction projects. The current building seismic design code(DSDC) (GB50011-2001), used a constant (maximum of earthquake affecting coefficient)to determine the value of maximum considered earthquake, did not fully consider the recent advancement of the knowledge of research on seismic hazard in mainland China. Some recent devastating earthquakes have indicated that the MCE-level acceleration specified in the DSDC may be underestimated. The same ductility provisions in DSDC are not assumed to provide the uniform additional safety margin against failure in different seismic zones. The ratio of maximum considered earthquakes (2% probability of exceedance in 50 years) and design basis earthquakes (10% probability of exceedance in 50 years) have been discussed in this article based on data of the new generation of Chinese seismic zonation map, using probabilistic seismic hazard analysis. It is shown that the ratio decreases as the acceleration value increases, and do not obey strict lognormal distribution, but, ratio on Ⅱ site on is approximate to lognormal distribution. Constant (seismic influence coefficient) for 90-380gal district in DSDC is roughly appropriate, whereas MCE-level ground motion parameters based on Constant for above 380gal areas in DSDC is significantly underestimated. The basic space distribution characteristics of ratio on Ⅱ site is that low value is associated with weak seismic environment, and vice versa.

  SE06-D5-PM2-P-030 (SE06-A017)
 
The Application of InSAR to Mining Area Subsidence Monitoring
Yaqiong #+
Institute of Earthquake Science, China Earthquake Administration, China
#Corresponding author: yayaday@163.com +Presenter

Huating Coalfield of Gansu Province, is the most thick coal seam of poly section in the Ordos Basin. The limestone resources are distributed in Pingliang City and Huating County.

The ground subsidence refers to the ground elevation decreased due to natural or man-made factors. The ground subsidence due to natural factors is a widespread phenomenon in the geological history, which is inevitable. Man-made factors refer to underground mining, which destroys the original rock body stress state of equilibrium, and makes the surrounding strata of the goaf, even the surface, move and deform. The ground deformation leads to the deformation and damage of the buildings, which affects the survival environment of industrial construction and agriculture production. The mining subsidence perplexes and hinders the economic development and environmental protection in the mining area. It can even cause earthquakes.

The mine tremor is also called “rock burst” in the mining industry. Main causes of mine tremor include: collapse, falling and gas outburst caused by mining directly; earthquakes caused by mining indirectly, which means rock rupture and strain release due to stress concentration under certain tectonic environment. The mine tremor is abrupt and can cause chain reaction. We must strengthen the prevention.

Interferometry SAR is an emerging earth observation technique, which is especially useful in cartography and surface subsidence survey. PS-InSAR is developed based on InSAR, which can detect deformation of millimeter level. Most PS-InSAR application and research have mainly focused on the monitoring of urban surface subsidence. There is relatively less application and research used to monitor surface subsidence in mining area.

In our research, PALSAR data were used to generate deformation interferograms. Characteristics of coherence as well as phase patterns on L band deformation interferograms were studied. By processing 24 SAR images from November 2006 to March 2011 covering the experiment area, we discussed the common master acquisition selection, image registration, phase unwrapping and other strategic technologies in PS-InSAR. The deformation rate in the line of sight is from about -18 to 17mm/yr. We made a straightforward analysis of subsidence reason and gave some suggestions.

  SE06-D5-PM2-P-031 (SE06-A020)
 
Research on Late Quaternary Activity of the Eastern Segment of Brahmaputra Fault Zone
Fangtou TANG#+
Institute of Geophysics, China Earthquake Administration, China
#Corresponding author: fttang@sina.com +Presenter

This study utilizes the high-resolution image data (Google Earth)in combination with detailed field investigation on the eastern segment of Brahmaputra fault zone, through GPS data, trenching and radiocarbon dating of charcoal samples, investigates the late Quaternary activity of the eastern segment of Brahmaputra fault zone. The recent observational data of GPS shows that the strike-slip rate is 1~3mm/a and extrusion rate is 1~2mm/a at the eastern segment of Brahmaputra fault zone. Mirui trench have revealed that the tenth layer silty soil was dislocated and its ages is 5650±50cal.a BP. It is found that the eastern segment of Brahmaputra fault zone is active since Holocene. We analyze the landscapes and calculate vertical slip rate is 1~1.2mm/a. Caimen trench have revealed three different of deformed strata, which display three paleoearthquake events. The first paleoearthquake event is 10220±30cal.a BP , the second event is 8800±190cal.a BP, the third event is 5650±50cal.a BP. These results indicate that the slip rate of eastern segment of Brahmaputra fault zone is still active during Holocene, but its active strength is lower.

  SE06-D5-PM2-P-032 (SE06-A021)
 
Tsunami Events Recorded in Chinese Historical Document
Honglin HE#+
Institute of Geology, China Earthquake Administration, China
#Corresponding author: honglinhe123@vip.sina.com +Presenter

"Tsunami' is from Japanese language, termed as an extremely large wave with long wavelength in the sea caused by earthquake, volcano eruption or landslide on sea floor, etc. China has long civilization history (longer than 3700 a) and long coastline. In historical archives, there are many records concerned with tsunamis and seiches. However, different from the modern concept of tsunami, in ancient China tsunami (translated to "Haixiao" or "Haiyi" in Chinese language) were large waves in sea, either tsunami wave, big storm or tide wave. Therefore, it is necessary to identify a true tsunami from "Haixiao" or "Haiyi" records before your evaluating tsunami risk along the coast of China mainland. In our researches on paleo-tsunami and tsunami-risk-assessment, a detailed investigation of historical documents is very important and the first step. Along the coast of China mainland, there are 8 historical tsunami events occurred from BC. 48 to now. The two earliest ancient tsunami records occurred in Bohai sea and dated back BC 48 and AD 171. Two tsunami events occurred in last century, which were associated with local earthquakes, M7.3 earthquake of 1918 near Nanao Island in South China sea and M6 earthquake of 1948 in Huanghai sea near Weihai, Shandong Province. Other three tsunami records in East China Sea were associated with those earthquake occurred in Nankai trough, Japan Island. They are Japan earthquake of 1498, Nakai M8.4 earthquake of 1707 and Nankai M8.4 earthquake of 1854.

  SE06-D5-PM2-P-033 (SE06-A024)
 
Preliminary Volcanic Hazard Zonation in Jinlongdingzi Area, Longang Volcano Cluster, Jilin Province, China
Bo ZHAO1#+, Zhida BAI2, Debin XU2
1 Institute of Geology, China Earthquake Administration, China, 2 China University of Geosciences, China
#Corresponding author: 276057048@qq.com +Presenter

Longgang volcano cluster is 150 km away from the Tianchi volcano, located in the Jingyu and Huinan counties, Jilin province, China. It had a long active history and produced hundreds of volcanoes. The latest eruption was occurred between 1500 and 1600 years ago by Jinlongdingzi (JLDZ) volcano which had several eruptions in the history.

Based on the products and eruption style, these volcanoes can be divided into four types: Strombolian, Hawaiian, Sub-plinian and Maar. Strombolian and Hawaiian are two common eruption ways, producing lava, cinders and bombs. JLDZ volcano eruption type is Sub-plinian, which produced a great mass of tephra fallout, covered 260 km2. Dalongwan volcano near JLDZ volcano is a typical maar lake with base surge deposits.

The major types of volcanic hazards in JLDZ area are lava flow, tephra fallout and base surge. According to the physical parameters of historical eruption, we propose the preliminary volcanic hazard zonation in JLDZ area.

The air fall deposits are the most dangerous products in JLDZ. In a radius of about 2km around the volcano, it is highly dangerous region. Between 2 km to 9 km around the volcano, it is moderate risk area. Out of the 9km, it is the low risk region. Lava flow is controlled by topography. From the Jinchuan town to Houhe village near the volcano, they are low-lying areas. If it erupts, these areas must be in danger. Base surge is also powerful. In the radius of about 4 km, it is the highly dangerous region. Out of the 4 km, it is the low risk region. The water in the lake is a potential hazard and must be considered.

  SE06-D5-PM2-P-034 (SE06-A029)
 
Infrasound Data Analysis Results Using Portable and KMA's Infrasound Networks
Young-Soo JEON#+, Won-Jung YOON, Dukkee LEE, Eunyoung JO
National Institute of Meteorological Research, Korea Meteorological Administration, South Korea
#Corresponding author: ysjeon@korea.kr +Presenter

KMA recently installed two infrasound tations at Yang-gu(YGS, 2011) and Chul-won(CWS, 2013) to prepare from the nuclear threat and missles activities of North Korea. NIMR recently purchased portable infrasound equipment nicluding sensors, digitizer and recording port. We used KMA network data and observed data from field test using portable sensors to review the data quality and yield the initial results. The purpose ogf this study is to collect the data sets of explosions, and man made signals to analyze the data sets of known source to prepare for future purposes.

The waveforms of YGS, and CWS do not record good quality missle signals clearly. It may be the raypath of the signal do not match well with the direction of wave propagating from source to the sites. Or elase, the sites located in the blind zone from the source region to propagate path. The observed records at the field test site show clear signals from the known source direction. data processing results indicated the known direction(back-azimuth) and average speed of the signals. KMA's infrasound research is in initial stage which require more instruments and data sets to analyze. Deploying proper array network and analysis data of known source will be the right validating method for further research of infrasound signals.

  SE06-D5-PM2-P-035 (SE06-A031)
 
Magnitude Estimation Using the P-Wave Amplitude for Earthquake Early Warning in South Korea
Ha-Seong LEE#+
National Institute of Meteorological Research, Korea Meteorological Administration, South Korea
#Corresponding author: hslee321@korea.kr +Presenter

Earthquake Early Warning system in South Korea is designed to estimate magnitude using peak amplitude of displacement in the first four seconds after the arrival of the P-wave. The method used in this study to estimate magnitude of an earthquake from the P-wave was based on the ElarmS method which uses empirical scaling relationship. P-wave peak amplitude is easily influenced to the noise because P-wave amplitude is relatively smaller than S-wave amplitude.Therefore, it will be able to detect incorrect P-wave arrival that causes detecting incorrect peak amplitude.Thus, this study was recalculated manually for EEW system performance verification.We selected 19 earthquakes which analyzed by EEW system during 2014 in South Korea.And it was compared manual recalculation result and auto analysis result (EEW system).However, some results showed that incorrect peak amplitude value at some observatory as incorrect detection of the P-wavearrival. The purpose of this study is to improve the performance of the EEW system by describing the characteristics of incorrect cases.

  SE06-D5-PM2-P-036 (SE06-A032)
 
Development of Tsunami Detection Algorithm for Application to Korean Surge-Gauge
Jun-Whan LEE#, Sun-Cheon PARK+
National Institute of Meteorological Research, Korea Meteorological Administration, South Korea
#Corresponding author: junwhan89@korea.kr +Presenter

Long-period seismic sea wave mainly caused by a large submarine earthquake is called tsunami. Sumatra tsunami occurred in 2004 and Tohoku tsunami occurred in 2011 show how the unexpected tsunamis are dangerous not only to neighboring countries but also to distant countries. Korea also suffer from tsunamis occurred off the west coast of Japan in 1983 and 1993. In order to prevent loss of life and damage, several tsunami detection algorithms have been developed such as DART algorithm (Mofjeld, 1997) and TEDA (Bressan and Tinti, 2011). However, the Ulleungdo surge-gauge in Korea operated by Korea Meteorological Administration (KMA) has been only used to monitor the water wave. In this study, we developed a tsunami detection algorithm called KTDA which is applicable to the Ulleungdo surge-gauge.  

The procedure of KTDA could be described in terms of three distinct stages. First, because the Ulleungdo surge-gauge data contain not only spikes but also missing values, the Tukey 53H method which compares the filtering data and the observed data was used to remove the spikes. Second, the end-point fixing method (EPFM) was applied to fill the gap in real time. Finally, the tsunami detection algorithm modified so as to be applicable to any sampling rate was applied to the gap-filled data.

When the KTDA was applied to the Ulleungdo surge station data from March 9, 2011 to March 12, 2011 where the Tohoku tsunami has passed the East Sea, the overall performance was fairly accurate. More tests using long period of data should be needed to calibrate the thresholds of the tsunami detection algorithm.

  SE06-D5-PM2-P-037 (SE06-A034)
 
Source Characteristics of the 2013 Santa Cruz Islands Earthquake and its Aftershocks
Eun Hee PARK#, Sun-Cheon PARK+, Jun-Whan LEE, Duk Kee LEE
National Institute of Meteorological Research, Korea Meteorological Administration, South Korea
#Corresponding author: ungc1225@korea.kr +Presenter

In order to understand the characteristics of large tsunamigenic earthquakes, we analyzed the source process of the 2013 Santa Cruz earthquake (M8.0) on Feb. 6, 2013. The earthquake occurred near the plate boundary between the Australia and Pacific plates. In the region nearby this earthquake, usually small or medium-sized earthquakes occur. The M8.0 event in 2013 was largest earthquake in this region. According to the U.S. Geological Survey (USGS), 61 earthquakes with magnitudes greater than 5.5 occurred in Jan. 27 - March 8, 2013. Among them, eleven events happened for a week before the mainshock and the number of aftershocks in 30 days was 49.

We carried out teleseismic body-wave inversion to obtain the slip distribution of the earthquake. P waveform data from 19 stations in the epicentral distance between 30° and 90° were used. And the source time window was assumed as 120 seconds by the duration of high-frequency energy radiation. The inversion result shows that the earthquake occurred on the northwesterly striking (291°) and shallowly dipping (24°) fault plane. We tested some input source parameters to get the final inversion results. As rupture velocity increases, the variance between the observed and synthetic waveforms tends to be increased and magnitude and maximum displacement tend to get small. Rupture velocity of 2.0 km showed the smallest variance. Moment magnitude was obtained to be 7.9 and maximum displacement was 1.4 m. Our result of slip distribution shows large slip area near the hypocenter in general. To verify our slip distribution and inversion results, we carried out tsunami simulation using the slip distribution, and then compared the simulated tsunami with observed data.

  SE06-D5-PM2-P-038 (SE06-A042)
 
Sediment Pathways Across the Slopes of the Erosional Japan Trench
Marie-Helene CORMIER1#+, Toshiya FUJIWARA2, Leonardo SEEBER3, Cecilia MCHUGH4, Toshiya KANAMATSU2, John W. KING1
1 University of Rhode Island, United States, 2 Japan Agency for Marine-Earth Science and Technology, Japan, 3 Lamont Doherty Earth Observatory, United States, 4 Queens College, City University of New York, United States
#Corresponding author: milenecormier@gmail.com +Presenter

Until the 2011 Mw9.0 Tohoku earthquake, the role of giant tsunamis and earthquakes as agents of sediment dispersal and accumulation at erosional trenches was largely under-appreciated. Decades of seismic reflection surveys and sediment coring did document a general sedimentation pattern. Terrigenous sediments accumulate across the trench slope as a relatively thin slope apron, whereas sediments at the trench axis are either accreted to the small frontal wedge, or subducted. A series of cruises carried out after the 2011 earthquake and tsunami revealed a variety of unexpected sediment dispersal mechanisms, such as tsunami-triggered sheet turbidites. Furthermore, new piston cores collected across the trench slope indicate significant along-trench and across-trench variability in the way that sediments were mobilized by the 2011 event. Hence, the combined dataset suggests that giant earthquakes and tsunamis may be important agents for dispersing sediments across the trench slope. To complement these new observational data, we have calculated the theoretical pathways of sediments across the trench slope using existing multibeam bathymetric grids. Pathways are modeled based on the simple assumption that transport direction is dictated by the slope azimuth only (not slope gradient). Results indicate that (1) most pathways issued from the shelf and upper slope terminate near the top of the small frontal wedge, and thus do not reach the trench axis; (2) In turn, sediments transported to the trench axis can only be derived from the small frontal wedge or from the subducting Pacific plate; (3) Very few direct pathways from the shelf area drain to the trench. This results are consistent with existing seismic profiles across the trench slope, which reveal that the slope apron does not extend as far as the frontal wedge, and that the sediment fill in the trench is surprisingly  thin (<< 500 m)

  SE07-15-D5-PM2-P-009 (SE07-15-A002)
 
Conductivity Structure of the Mantle Transition Zone Beneath North China
Qinghua HUANG1#+, Guangjing XU2, Ji TANG3, Makoto UYESHIMA4
1 Peking University, China, 2 Institute of Geology and Geophysics, China Academy of Sciences, China, 3 Institute of Geology, China Earthquake Administration, China, 4 The University of Tokyo, Japan
#Corresponding author: huangq@pku.edu.cn +Presenter

The deep structure plays an important role in understanding the related geodynamics. In this study, we investigated the electrical conductivity structure of the mantle transition zone in North China, based on the geomagnetic data from the permanent stations. We adopted the remote reference method and the robust estimation to obtain the high quality data. The geomagnetic deep sounding (GDS) response with periods of 105-107 seconds was obtained by using long period observation data and transformed into an equivalent scalar magnetotelluric (MT) transfer function. The ρ+ inversion indicates that conductivity discontinuity surfaces exist at depth around 417 km and 850 km. The smooth conductivity models of Occam inversion were also obtained and compared with some existed models. We found that the conductivity of the mantle transition zone in the east and west of the North China are different. The conductivities of the mantle transition zone near the Ordos in the west of North China are similar to that of Tucson in North America, while the conductivities in the east part are approximately 2-5 times higher. This feature may correspond to the subduction of the Pacific plate.

This study is supported partially by the National Basic Research Program of China (2014CB845903) and the National Natural Science Foundation of China (40974041).

  SE07-15-D5-PM2-P-010 (SE07-15-A009)
 
A Comparison Study of High Resolution Geomagnetic Observation Systems Using HTS-SQUID Magnetometer for Earthquake Detection
Yuta KATORI1#+, Kan OKUBO1, Tsunehiro HATO2, Akira TSUKAMOTO2, Keiichi TANABE2, Nobuhito ONISHI3, Chikara FURUKAWA3, Shinji ISOGAMI4, Nobunao TAKEUCHI5
1 Tokyo Metropolitan University, Japan, 2 International Superconductivity Technology Center, Japan, 3 Tierra Tecnica, Japan, 4 Fukushima National College of Technology, Japan, 5 Tohoku University, Japan
#Corresponding author: katori-yuta@ed.tmu.ac.jp +Presenter

Magnetic field changes associated with earthquakes have been investigated previously (1964 Stacey). And furthermore, geomagnetic field changes before and after an earthquake is reported (1994 Johnston et al.) Our research group also reported successful observation results of “co-faulting” Earth’s magnetic field changes due to piezomagnetic effects caused by earthquake rupturing in 2008 Iwate-Miyagi Nairiku earthquake of M7.2 (2011 Okubo et al.) using the flux-gate magnetometers. This is an important finding; the magnetic fields propagate from the sources to the observation site at a speed of light in the crustal materials. Further efforts could lead us to a new system for super-early warning of destructive earthquakes with the magnetic measurements. On the other hand, this observed result suggested that the geomagnetic variation signal accompanying fault movement, whose sources are the earthquake piezomagnetic effects, is very small; the observed change of geomagnetic field is approximately several hundred pico-tesla.

Therefore, development of a high-sensitive magnetometer system for geomagnetic observation is very important. Since March 2012 we have introduced long-term precise geomagnetic observations using high-temperature-superconductor based superconducting-quantum-interference-device (HTS-SQUID) magnetometer system Unit No.1 (mark I) at Iwaki observation site (IWK) in Fukushima, Japan. Additionally, since October 2014, we have also introduced the new HTS- SQUID magnetometer system Unit No.2 (mark II). The sampling interval of the magnetometer is 0.02 sec. The system clock has been synchronized by use of GPS signals. A high-resolution accelerometer is also installed at observation point.

In this study, we make a comparison evaluation of the performance of the geomagnetic field observation systems. By our evaluation, it is clarified that the resolution of our HTS-SQUID magnetometer systems is about a few or several pico-tesla. Moreover, we show the observation results of geomagnetic field changes associated with the earthquake of M5.9 (on September 19, 2013) using our high-sensitive magnetometer system.

  SE07-15-D5-PM2-P-011 (SE07-15-A013)
 
Equivalent Magnetization Over the World's Ocean from WDMAM v.2
Yujin CHOI1, Jerome DYMENT1#+, Erwan THEBAULT2, Mohamed HAMOUDI3, Vincent LESUR1
1 Institute of Earth Physics of Paris - French National Centre for Scientific Research, France, 2 University of Nantes / French National Centre for Scientific Research, France, 3 University of Science and Technology Houari Boumediene, Algeria
#Corresponding author: jdy@ipgp.fr +Presenter

As a by-product of our recent work to build a candidate model over the oceans for the second version of the World Digital Magnetic Anomaly Map (WDMAM v.2), we derived global distributions of the equivalent magnetization in oceanic domains.

In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface assuming a unit magnetization. In a second step, we adjust this model to the existing marine magnetic anomaly data in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies. The ratio between the standard deviations of data and model on each sliding window represents an estimate of the equivalent magnetization under the considered magnetized source geometry. The resulting distributions of equivalent magnetization are further discussed in terms of age of the oceanic lithosphere, spreading rate at which it was formed, and presence of anomalous crust in hot and cold spot areas. 

Global marine magnetic data sets and models represent a useful tool to assess the first order magnetic properties of the oceanic lithosphere at a global scale.

  SE08-D5-PM2-P-009 (SE08-A001)
 
CO2-Rich Fluids and Metasomatism in the Lithospheric Mantle Beneath Jeju Island, South Korea: Evidence from Peridotite Xenoliths
Yonghoon WOO+, Minyoung SEO, Hyungsuk KIM, Kyounghee YANG#
Pusan National University, South Korea
#Corresponding author: yangkyhe@pusan.ac.kr +Presenter

Abundant spinel harzburgite to lherzolite Peridotite xenoliths are trapped in Quaternary intraplate alkali basalts in Jeju Island. Studied peridotite xenoliths were silica- and LREE-enriched, containing late-stage secondary orthopyroxene as the main pervasive metasomatic mineral. Primary CO2-rich inclusions with negative crystal shapes (5-30µm in diameter) are trapped in the late-stage secondary orthopyroxene or fine-grained neoblasts, although they are extremely rare. During microthermometry, solid CO2 melting temperatures of the inclusions are -56.6℃ (± 0.8℃), indicating the presence of essentially pure CO2 phase. Homogenization temperatures of CO2 to the liquid phase range from - 34 to -22℃, corresponding to CO2 density of 1.1–1.0 g/cm3.  The high CO2 density and a negative crystal shape support that the entrapment of the fluids occurred at lithospheric mantle conditions prior to sampling by upwelling alkali basalt.

Major element analysis of mineral phases indicates no chemical zoning and homogeneous chemistry. The mg# of olivine, orthopyroxene and clinopyroxene and the Cr# of spinel is relatively constant (ol: 89-92; opx: 89-92; cpx: 89-92) and variable (9-52), respectively, representing residues left after variable fractional melt extraction. In contrast to their depleted major element compositions, the clinopyroxenes of the xenoliths are mostly enriched in incompatible trace elements, exhibiting enrichment in light rare earth elements (LREE), negative Ce-anomalies, and depletion in Ba and high field strength elements (HFSE; e.g., Nb-Ta, Zr-Hf, Ti). The chemical evidence, in addition to the formation of secondary orthopyroxene, clearly indicates that Jeju peridotite series have been subjected to different degrees of metasomatism by subduction-related silica- and LREE-enriched fluids. Although more research be conducted on the lithosphere environment, Silicate component and trace elements that are moved by the CO2 –rich fluids supported the metasomatism in the lithospheric mantle.

  SE08-D5-PM2-P-010 (SE08-A002)
 
Reflection from the Base of Oceanic Lithosphere Observed from Active-Source Seismic Data
Akane OHIRA1#+, Shuichi KODAIRA2, Yasuyuki NAKAMURA2, Gou FUJIE2, Ryuta ARAI2, Seiichi MIURA2
1 Yokohama National University, Japan, 2 Japan Agency for Marine-Earth Science and Technology, Japan
#Corresponding author: oohira-akane-jp@ynu.jp +Presenter

Understanding of structure of the oceanic lithosphere is an important clue for the study of the dynamics of plate tectonics. The oceanic lithosphere is composed of the oceanic crust and a part of upper mantle. So it is necessary to obtain seismic reflection data for the crust and wide-angle reflection/refraction data for the upper mantle simultaneously. However, there are few studies which covered wide range of ages of the typical oceanic plate continuously by using latest seismic techniques including both seismic reflection and refraction methods.

In 2014 we conducted an active-source seismic survey in southeast of Shatsky Rise along the 1130km-long line which covers the old plate formed from Late Jurassic to the Early Cretaceous (e.g. Nakanishi et al., 1989). Five ocean bottom seismometers (OBSs) were deployed by R/V Kairei. We used an airgun array with a total volume of 7,800 cubic inches with firing at intervals of 200m as controlled sources. Multi-channel seismic reflection (MCS) data were also collected with a 444-channel, 6,000-m-long streamer cable.

On MCS data strong variation of the Moho were imaged. The clear and sharp Moho was imaged up to about 50km from southwest end, then the Moho was changed to be ambiguous from this point. In some areas, the Moho was not identified. The thickness of the sedimentary layer was about <0.3km except area around northeast end of survey line. The apparent velocity of uppermost mantle refractions observed on the OBS record was about <8.6km/sec. We also identified reflected waves from the upper mantle, which are similar to mantle reflection phases observed in northwest Pacific Basin (Kaneda et al., 2010). As a result of forward modeling (Fujie et al., 2008) of the mantle reflection phases, depths of these reflectors were about 40km-65km, some of which may correspond to the lithosphere-asthenosphere boundary.

  SE08-D5-PM2-P-011 (SE08-A004)
 
Palawan Ophiolite as a Possible Supra-Subduction Zone Type (SSZ): Evidences from Mantle Olivine-Spinel Geochemistry
Emmanuel CODILLO#+, Carlo ARCILLA, Darren DERPO, Nobee CODAMON
University of the Philippines Diliman, Philippines
#Corresponding author: emmanuelcodillo@gmail.com +Presenter

The southern portion of the Palawan Island comprises a complete ophiolite sequence from upper mantle lithologies grading into pillow lavas and overlying sediments. It is thrusted over the northern Palawan continental block. Weathered portions of these ultramafics are the source of the nickel and iron laterite ores that are currently being mined and processed using high pressure acid leaching. In this paper, we present new field mapping and mineral data from the ultramafic section of the ophiolite which generally consists of refractory clinopyroxene-bearing harzburgites, wehrlites and dunites. Due to serpentinization, primary minerals such as olivine, orthopyroxene and clinopyroxene have been altered to secondary minerals except for some relict grains. Mineral chemistry data of olivine, orthopyroxene, clinopyroxene and chromian spinels were obtained by an electron probe microanalzyer (EPMA; model JXA-8230). Our initial data show that the mineral compositions reveal high Cr # (0.6-0.74), low Mg # (0.51-0.59) and very low Ti wt. % content (<< 0.01 wt. %) for chromian spinel; high Fo (Fo90.0-92.1) for olivine, suggesting refractory character where previous melt extractions could have depleted the source with incompatible elements. This suggest that the dominantly refractory harzburgites, wehrlites and dunites of the Palawan ophiolite were melting residues formed from high degrees of partial melting (~ 20 %) probably in hydrous conditions. Moreover, the similarities between the Cr# of  the ultramafics of  the southern Palawan and the chromite pods of the Ulugan bay (central, Palawan) suggest that these widely separated ultramafic suites could have been derived from a single oceanic lithosphere that was dismembered during its emplacement. However, further examination of whole-rock and individual mineral bulk and trace element geochemistry are still needed to support and confirm the suggested supra-subduction zone setting of the Palawan ophiolite and its association to boninite magmatism.

  SE09-D5-PM2-P-012 (SE09-A002)
 
Possible Hazards from Sumatran Volcanoes: A Morphometric Investigation
Christopher A. MCCALLUM#+, Caroline BOUVET DE MAISONNEUVE
Nanyang Technological University, Singapore
#Corresponding author: mcca0002@e.ntu.edu.sg +Presenter

Volcanoes grow as they erupt, adding sequential layers of lava and ash. Digital elevation models (DEM) can be used to measure numerous morphometric parameters, and a few algorithms have recently been developed to enable rapid and self-consistent analyses of morphological data. We have used the NETVOLC (Euillades et al., 2013) and MORVOLC (Grosse et al., 2012) algorithms in order to define volcanic edifice boundaries, compute edifice volumes, and estimate morphometric parameters from SRTM-based DEMs of twenty-five active volcanoes distributed along the arc in Sumatra. The detailed investigation of individual volcanoes enables to quantify the changes in slope from the base to the summit regions, the ellipticity of the edifice and whether this relates to the local stress field, the irregularity of the elevation contours and the presence of scarps or incisions, amongst many other shape parameters or ratios. In the case of Marapi, the slopes are fairly constant on the northern and eastern flanks whereas the southern and western flanks have steep incisions or collapse scars, like the summital Bancah depression. The edifice shows a tendency toward increasing ellipticity with elevation and the elongation is NE-SW trending. These observations highlight tectonic-volcanic interactions involving the Sumatran fault, which is NW-SE trending and delimits the edifice to the SW. The comparison of multiple edifices within Sumatra shows a slight northward trend of increasing volcano height/basal width ratio. We have qualitatively classified the volcanoes into three morphometric groups and, as expected, the stratovolcanoes are the closest to having perfectly conical shapes and are the less elliptical and irregular. There is no obvious variation in volcano morphometric type with latitude. However, there is a clear gap in the presence of active volcanoes between 0.5-3° N. This spatially coincides with the subduction of thicker and younger oceanic crust (mid-oceanic ridge).

  SE09-D5-PM2-P-013 (SE09-A005)
 
Using WOVOdat Tools to Understand the Evolution of Volcanic Unrest
Karine TAN1#+, Christina WIDIWIJAYANTI2, Fidel COSTA2, Nang Tin Zar WIN1, Chris NEWHALL3, Antonius RATDOMOPURBO4, Mariton BORNAS5, Mary Jane CATAPANG5, Maricel CAPA5, Naning AISYAH6, Prayitno ASHURI6, Raditya PUTRA6, Hanik HUMAIDA6, Hetty TRIASTUTY7, Novianti INDRASTUTI7, Hery KUSWANDARTO7, Dawn SWEENEY RUTH1
1 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 Nanyang Technological University, Singapore, 3 Mirisbiris Garden and Nature Center, Philippines, 4 Geological Agency, Indonesia, 5 Philippine Institute of Volcanology and Seismology (PHIVOLCS), Philippines, 6 Center for Research and Technological Development Kegunungapian (BPPTK), Indonesia, 7 Center for Volcanology and Geological Hazard Mitigation, Indonesia
#Corresponding author: karinetan@ntu.edu.sg +Presenter

The World Organization of Volcano Observatories’ Database of Worldwide Volcanic Unrest (WOVOdat) is an international effort to develop common standards for compiling and storing data on worldwide volcanic unrest in a centralised database for reference during volcanic crises, comparative studies, and research on pre-eruption processes. WOVOdat has also developed new web-tools to help users query, visualise, and compare volcano monitoring data. These are especially useful because during periods of volcanic unrest, further activity may be anticipated based on knowledge of previous activity at the restless volcano and comparisons to unrest and eruptions at similar volcanoes.

This study uses WOVOdat’s newly developed web-tools to understand the evolution of volcanic unrest at Pinatubo, Mayon (Philippines), Merapi, Kelut, Sinabung (Indonesia) and Mt St Helens (USA) recent eruptions. These high-risk active volcanoes range from plugged to openly degassing systems, produce different styles of eruptions with varying Volcanic Explosivity Index, (VEI) and have caused devastating eruptions over the last thirty years. The tools in WOVOdat allow us to perform time-series comparisons on multi-parameter monitoring data sets correlated to different phases of an eruption between the volcanoes.

Preliminary comparisons show an increase in SO2 emission at Pinatubo a week before the Plinian eruption (1991) but not before the Mt St Helens dome forming eruption (2004). We are also able to observe an exponential increase in the number of volcanic earthquakes about two weeks prior to both Plinian eruptions at Pinatubo (1991) and Mt St Helens (1980).

Identifying these precursors from monitoring data will allow us to better anticipate the evolution of the volcanic unrest and implement timely mitigation measures. In the future, statistical analyses can be applied to data derived from WOVOdat to aid in probabilistic eruption forecasting when more continuous multi-parameter monitoring data becomes available.

  SE09-D5-PM2-P-014 (SE09-A007)
 
What is the Eruptive Potential of Marapi Volcano (Sumatra)?
Dini NURFIANI1#+, Christopher A. MCCALLUM2, Hendra GUNAWAN3, M. Nugraha KARTADINA3, Benoit TAISNE2, Caroline BOUVET DE MAISONNEUVE2
1 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 Nanyang Technological University, Singapore, 3 Center for Volcanology and Geological Hazard Mitigation, Indonesia
#Corresponding author: dnurfiani@ntu.edu.sg +Presenter

Marapi is the most active volcano in Sumatra (Indonesia). In the past 15 years, the volcano erupted more than 80 times. While the eruptions were usually small (VEI 1-2), such frequent activity, the volcano’s proximity to densely populated areas, and its potential for more violent eruptions make Marapi a prime candidate for increased monitoring. In our study, we investigate Marapi’s past volcanic activity, including the most recent eruptions, its current magma storage conditions and pre-eruptive dynamics in order to assess the potential for more violent eruptions. We sampled twelve different eruptive units spanning the long-term history of the volcano, and we identify three unusually explosive eruptions, two of them from lateral vents. The oldest of the three eruptions formed the Sikumpar Tuff Cone on the northeastern flank. The cone is 1-1.5 km in diameter, >50 m high, and consists of a vertical gradation from dominantly phreatic to dominantly magmatic deposits. The youngest of the three eruptions formed a depression, the Kayutanduk Maar, on the trace of the Sumatran fault to the southwest. The deposits are >30 m thick and are exclusively phreatic. The third eruption, which could have been sourced from the summit vent, produced a thick (>30-50 m) and massive basaltic-andesitic pyroclastic flow, which is preserved on the southwestern flank. The deposit consists of cm- to dm-sized crystal-poor scoria in a matrix of ash. In light of the observed deposits, we investigate the hazard potential from tephra fall and pyroclastic flows by numerically simulating usual and the worst-case scenarios. By combining petrology with the analysis of recent seismic data (eruptive period of January 2013 to December 2014), our study will yield crucial information on the state of the volcano and enable us to better estimate the hazards associated with future eruptions.

  SE09-D5-PM2-P-015 (SE09-A008)
 
Crustal Deformation Associated with the Unrest of Azumayama Volcano
Satoshi MIURA#+, Mare YAMAMOTO, Masahiro ICHIKI, Takeshi NISHIMURA, Yusaku OHTA, Tomotsugu DEMACHI
Tohoku University, Japan
#Corresponding author: miura@aob.gp.tohoku.ac.jp +Presenter

Azumaya Volcano is an active volcano located in northeastern Japan and have erupted at and around the Oana crater within recorded history, and currently a large fumarolic area extends across its southern and eastern flanks (Japan Meteorological Agency, 2013). Recent seismicity between 2001 and 2009 are characterized as repeating active and quiet periods with intervals of around 2 to 3 years, while it shows steady activity after 2010 (Japan Meteorological Agency, 2014a). Seismic activity looks slightly declined after 2013, however, it gradually increased since October 2014. A volcanic tremor with a duration of about 35 minutes occurred on December 12, 2014, and the monthly number of volcanic earthquakes in December 2014 counted 576, which is the largest since November 1998 (Japan Meteorological Agency, 2014b).

Japan Meteorological Agency (JMA) deploys 6 continuous GPS sites around the volcano. The data are processed using the precise point positioning strategy (Zumberge et al., 1997) of GIPSY-OASIS II ver. 6.2 with IGS08 precise ephemerides and GMF mapping functions (GMF, Boehm et al., 2006). Since the wide area of northeastern Japan still suffers the long lasting postseismic deformation following the 2011 Tohoku-oki earthquake (M9.0), we try to extract volcanic deformation related to the unrest of the volcano by fitting an approximation function of time consisting of linear, logarithmic, annual, and semi-annual terms. The coefficients of each term are estimated by the least-squares method for the period between April, 2011 and September, 2014.

Resulting displacements around the volcano for the period between October to December, 2014 show radial expansion and slight uplifting, which can be roughly modeled with an point pressure source at a depth of 3.4 km just beneath the summit of Issaikyozan.

Acknowledgement: Authors are grateful to the Japan Meteorological Agency and the Geospatial Information Authority of Japan for providing GNSS data used in this paper.

  SE09-D5-PM2-P-016 (SE09-A011)
 
Linking Petrology to Monitoring Data by Diffusion Modeling: A Possible Interpretation of Recurrent Seismic Swarms at Gede
Daniel KRIMER1#+, Fidel COSTA2
1 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 Nanyang Technological University, Singapore
#Corresponding author: daniel1@e.ntu.edu.sg +Presenter

Subduction-zone volcanism produces a variety of compositions and eruption styles, but silica-rich explosive eruptions pose the most direct threat for those around the volcanoes. Gede is a composite arc-volcano showing evidence of recurrent silicic eruptions and is a hazard to its 1 million residences and the dwellers in Jakarta and Bandung. Here we present the results of a 3D simulation-based approach in diffusion modeling, and a possible link between the estimated time-scales of magmatic processes and recent monitoring data.

Holocene pyroclastic units from Gede show characteristic reverse zoning of mafic minerals as unambiguous evidence for magma mingling that has likely been triggering its explosive eruptions. Core to rim EPMA and LA-ICP-MS trace element analyses of main phenocrysts reveal the details of repetitive magma recharge events. The cores of the phenocrysts have a low Mg/Fe and are surrounded by high Mg/Fe rims. Modeling the fast diffusive re-equilibration of Mg/Fe between the crystal cores and rims of orthopyroxene provides the time elapsed between the onset of recharge and eruption, which is on the order of a month. Slowly diffusing elements (i.e. Al, Ti), however, suggest a complex history of multiple rim growth events, which has been erased from the Mg/Fe record. High-resolution trace element profiles also advocate halted recharge events where unrest never made to eruption. Seismic swarms observed in the last years lasted about a month, however, an eruption never occurred. Thus, these seismic events may possibly mark new magma introduction to the system.

Our study shows that magma recharge events commence about a month prior to eruption in all of the Holocene units, thus implying a stable reservoir under Gede. This suggests that if new unrest occurred, the eruption would likely be imminent, but there would be enough time to assess monitoring signals and decide on potential hazard mitigation strategies.

  SE09-D5-PM2-P-017 (SE09-A016)
 
PHIVOLCS Volcano Database System (VDAS): Adapting and Moving Forward with the WOVOdat Schema
Maricel CAPA1#, Christina WIDIWIJAYANTI2, Antonius RATDOMOPURBO3, Nang Tin Zar WIN4, Alex BAGUET2, Mary Jane CATAPANG1+, Nerissa SENA1, Kenn John VERACRUZ1, Mariton BORNAS1, Renato SOLIDUM1, Chris NEWHALL5
1 Philippine Institute of Volcanology and Seismology (PHIVOLCS), Philippines, 2 Nanyang Technological University, Singapore, 3 Geological Agency, Indonesia, 4 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 5 Mirisbiris Garden and Nature Center, Philippines
#Corresponding author: macelcapa@gmail.com +Presenter

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) Volcano Database System (VDAS), adapted from the WOVODat system, has been implemented since 2012 and is currently in the stages of developing tools for automation of data processes.

Some of the data management tools that have been developed include online forms for remote data updating and retrieval for use by Volcano Observatories to a centralized VDAS server. These forms were designed specifically for daily observation data such as seismicity (Phase Data and Earthquake Count), visual observations of plume characteristics and crater glow, meteorology, hydrology and SO2 flux. Data retrieval management tools allow: a) querying record statistics for all monitoring stations for inventory purposes; b) listing of all records satisfying user-based parameters, and; c) downloading records based on user query. All of these tools require authentication for security purposes. Currently all Observatories for monitored active volcanoes (Mayon, Taal, Bulusan, Kanlaon, Hibok-Hibok, Pinatubo, Matutum and Parker) have mainstreamed forms for daily observation data. Other tools are in various stages of development or implementation, while new tools developed by the WOVODat Project have been recently integrated to VDAS for improved visualization.

PHIVOLCS’ adaptation of the WOVODat process was successfully completed with minimum but dedicated manpower for system management and data population and review. Minimum competency requirements for system management are basic knowledge in web development and database programming using PHP/MySQL and HTML, and for data population, rudimentary knowledge in spreadsheet software and, optionally, MySQL. The success of implementing the WOVODat system has been facilitated by the integrating efforts into PHIVOLCS’ strategic programs, projects and activities.

  SE09-D5-PM2-P-018 (SE09-A018)
 
Distribution of Pyroclastic Density Currents Determined by Titan2D Numerical Model at Mt. Baekdusan Volcano
Sung-Hyo YUN1,2#, Cheolwoo CHANG1+, Dongwoon KWON1, Yunjeong KIM1
1 Pusan National University, South Korea, 2 The Petrological Society of Korea, South Korea
#Corresponding author: yunsh@pusan.ac.kr +Presenter

We assumed the situation where an eruption column had been formed by the explosive Plinian eruption from Mt. Baekdusan and that the collapse of eruption column had caused pyroclastic density currents to occur. Based on this assumption, we simulated by using a Titan2D model. To find out about the range of the impacts of pyroclastic density currents by volcanic eruption scenarios, we studied the distance for the range of the impacts by VEIs. To compare the results by each volcanic eruption scenario, we set the location of the vent on the 8-direction flank of the outer rim and on the center of the caldera, the internal friction angle of the pyroclastic density currents as 35o, the bed friction angle as 16o. We set the pile height of column collapse and the vent diameter with various VEIs. We properly assumed the height of the column collapse, the diameter of the vent, the initial rates of the column collapse and the simulation period, based on the VEIs, gravity and the volume of the collapsed volcanic ash. According to the comparative analysis of the simulation results based on the increase of the eruption, the higher VEI by the increase of eruption products, the farther the pyroclastic density currents disperse. To the northwest from the vent on the northeast slope of the outer rim of the caldera, the impact range was 3.3 km, 4.6 km, 13.2 km, 24.0 km, 50.2 km, 83.4 km or more from VEI=2 to VEI=7, respectively. Once the database has been fully constructed, it can be used as a very important material in terms of disaster prevention and emergency management, which aim to minimize human and material damages in the vicinity of Mt. Baekdusan when its eruption causes the pyroclastic density currents to occur.

  SE11-10-D5-PM2-P-007 (SE11-10-A002)
 
Post-Opening of South China (East Viet Nam) Sea Geodynamic and Magmatic Evolution in Southern Viet Nam
Le DUC ANH1#+, Phung VAN PHACH1, Nguyen HOANG2,3, Nguyen NHU TRUNG1
1 Institute for Marine Geology and Geophysics, Vietnam Academy of Science and Technology (VAST), Viet Nam, 2 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 3 Geological Survey of Japan, Japan
#Corresponding author: leducanh010282@gmail.com +Presenter

New geophysical and structural analyses show that the SW tip of SW Sub-basin of East Vietnam Sea (EVS) has attenuated continental crust, not oceanic. The oceanic crust of EVS (South China Sea) does not spread to the west over the 112ºE longitude. The NW-SE Red River Fault, East Vietnam Fault Scarp and NW-SE striking Tuy Hoa Fault Zone were probably connected and acted jointly during the period of oceanic crust spreading (~ 32-17 Ma). This system may have controlled the oceanic spreading of the SW arm of the EVS to the SW. The NW-SE striking Tuy Hoa Shear zone may have played a role of transform fault and acted as SW boundary that has limited the spreading of oceanic crust further to the SW. The change from left- to right-lateral motion of NW-SE fault system may have led to the cessation of oceanic spreading in EVS and stimulated strong subsidence of Tertiary basins. Post- EVS opening, subsidence (extension) -related volcanism occurred in the oceanic crust and in the vicinity of the Hoang Sa (Paracels) Islands at two main episodes ca. 9 and <1 Ma, producing SiO2-poor and FeO-rich alkali basalt and nephelinite. Whereas, the contemporaneous subsidence-related volcanism appeared along extension faults running parallel to eastern Vietnam coastline from latitude 15°N to 10°N (underwater eruption of Iles Des Cendres in 1921) at two main episodes of 12 Ma and 1.5-0 Ma. The eruptions appear both on Ly Son (15°N) and Phu Quy (10°29’N) islands. The early comprises of high-SiO2, low-FeO tholeiite and the later, of low-SiO2, high-FeO olivine and alkaline basalt, implying melting sources were deepened with time. Although post-opening magmas occurred sporadically in the EVS and showed spatio-temporal differences, the volcanism was controlled mainly by subsidence (extension) tectonics, the activities are believed to govern the entire post-opening geodynamics.

  SE11-10-D5-PM2-P-008 (SE11-10-A006)
 
Young Basaltic Volcanism in Northern Palawan: OIB-Like Characteristics?
James Cesar REFRAN1#+, Carlo ARCILLA2
1 University of the Philippines, Philippines, 2 University of the Philippines Diliman, Philippines
#Corresponding author: jamesrefran@gmail.com +Presenter

The Philippines is dominated by SSZ-influenced magmatism. Very young lava flows in Northern Palawan form a large field with gentle topography suggesting  extensive, low viscosity flows. There are no active subduction zones beneath northern Palawan to cause typical arc volcanism. The rocks are basalts to basaltic andesites and straddle tholeiitic/calc-alkaline compositions but are not K-enriched. MORB-normalized spidergrams show enriched concentrations of Nb and other high field strength elements, further confirming the non-subduction zone origin. The lavas could be similar to OIBs found in the seamounts found in the South China Sea. The Nb-enriched Palawan lavas are the non-SSZ equivalents of Nb-rich lavas also encountered in the Sulu arc and Sulu seas, suggesting a fertile mantle source independent of SSZ contributions. This lava field, one of the largest in the Philippines, is to date the only  lavas in the Philippine archipelago with OIB characteristics.

  SE11-10-D5-PM2-P-009 (SE11-10-A010)
 
Petrology and Geochemistry of Apatite ± Whitlockite-Bearing Mantle Xenoliths from Southern Laos
Jürgen KONZETT1, Christoph HAUZENBERGER2#+, Katharina GROEBNER1, Anna-Katharina SIEBERER1, Nguyen HOANG3,4, Khoi Ngoc NGUYEN5
1 University of Innsbruck, Austria, 2 University of Graz, Austria, 3 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 4 Geological Survey of Japan, Japan, 5 Hanoi University of Science, Viet Nam
#Corresponding author: christoph.hauzenberger@uni-graz.at +Presenter

Cenozoic basalts are widespread throughout Southeast Asia and form what is called a “diffuse igneous province” consisting of tholeiites and late-stage, small-volume alkali basalts. We report the results of a petrological and geochemical study of a suite of spinel-lherzolites and ortho/clino-pyroxenites sampled by nepheline±leucite-bearing alkali basalts of the Bolaven Plateau/southern Laos. Lherzolites (ol+opx+cpx+sp+FeNi-sulfide) and pyroxenites (opx+cpx+FeNi-sulfide) show evidence for cryptic or modal metasomatism characterized by a strong enrichment of Li in cpx and opx with respect to ol (cryptic) and by the appearance of apatite rarely associated with minor phlogopite ± calcic amphibole. Two compositional types of apatite are present: (1) apatite characterized by low P2O5 (37.9-41.0 wt%) and low analytical totals (93.8-97.4 wt%) combined with high Na2O (0.9-1.6 wt%) indicative of a significant type-A carbonate-apatite component and (2) apatite with high P2O5 (40.5-42.4 wt%) and high analytical totals (97.7-100.9 wt%) combined with low Na2O (0.3-0.7 wt%). Low-P2O5 apatites show a restricted range in F and Cl (0.2-0.9 wt% F, 0.6-1.6 wt% Cl) compared to high-P2O5 apatites (0.3-3.1 wt% F, 0.3-4.1 wt% Cl). One apatite-bearing sp-lherzolite sample contains trace amounts of whitlockite-merrillite solid solution [Ca18Mg2(PO4)12[PO3(OH)]2-Ca18Na2Mg2(PO4)14] in addition to apatite+phlogopite+calcic amphibole. Whitlockite-merrillite is extremely rare in mantle rocks and has been known so far from only one locality in Siberia where its formation was ascribed to a distinct type of ±anhydrous REE-metasomatism (IONOV et al., 2006). In the sample from Laos, whitlockite-merrillite is always intergrown with apatite and was unambiguously identified using EMPA and micro-Raman spectroscopy. It contains 3.5-3.9 wt% MgO and 2.4-3.1 wt% Na2O, respectively. Thermometry of this sample yields 900-950°C for a pressure of 1.5 GPa.

  SE12-D5-PM2-P-009 (SE12-A001)
 
Volume Source Representations: A Unified Explanation Based on the Representation Theorem
Nobuki KAME1#+, Mie ICHIHARA1, Tetsuya KUSAKABE1, Hiroyuki KUMAGAI2
1 The University of Tokyo, Japan, 2 Nagoya University, Japan
#Corresponding author: kame@eri.u-tokyo.ac.jp +Presenter

There have been proposed two different volume changes from the seismic moment, the stress-free volume change dV_T and the confined volume change dV_C. The former is used in the moment tensor representation, while the latter is the actual volume change. These two volumes have been mentioned from the Eshelby’s virtual operation approach. However, why dV_T should appear in the moment tensor and why it is linked to Eshelby’s operation are not obvious. This study shows a unified explanation for their relation to the moment tensor following the representation theorem. The representation theorem gives the displacement field in terms of two surface integrals over the source surface: one is for the surface displacement and the other is for the surface traction. Only the first term has been considered for a seismic fault, because the second term vanishes due to the balance of the traction across the two adjacent fault surfaces. We here point out both terms are necessary in the representation for a volumetric source. Because the moment tensor uses only the first term, the second term contribution has to be involved as an additional surface displacement, which causes an imaginary volumetric change. Based on this idea, we derive an explicit representation of this imaginary volumetric change and relate dV_T to dV_C. Alternatively, we derive an equivalent volume source representation just by using the second term, taking the first term contribution into account as ‘imaginary stresses’. Our imaginary volume/stress approach will clarify the classic volume source theory.

  SE12-D5-PM2-P-010 (SE12-A002)
 
Mt. Baekdusan Area Volcanic Hazard Level Map According to Volcanic Eruption Scenarios
Eun-Kyeong CHOI#+, Sung-Wook KIM
GI Co. Ltd., South Korea
#Corresponding author: choiek@naver.com +Presenter

Mt. Baekdusan is recorded to have erupted at least nine times according to the database compiled by the Smithsonian Institution. One of those, a huge eruption in 946 AD, had a magnitude that earned it the name “millennium eruption.” This eruption is known to be the largest volcanic eruption on Earth in the past 2,000 years, tantamount to the magnitude of the 1815 eruption of Mount Tambora in Indonesia. The 946 eruption produced pyroclastic materials amounting to 96–120 km3 and spewed ash-clouds that were transported over thousands of kilometers so that volcanic sedimentation of 5 cm or thicker fell on the Japanese archipelago located over 5,000 km away from Mt. Baekdu. The eruption resulted in 20–30 billion tons of spewed magma and the formation of a 5-km-wide caldera lake. In case of a current explosive eruption of Mt. Baekdu, potential direct volcanic disaster would include volcanic ash, pyroclastic density currents, lahars, and volcanic floods. In this study, we constructed scenarios taking into account eruption-related parameters likely to be associated with pyroclastic density currents, lahars, and volcanic floods. We then ran simulations based on these scenarios. The Volcanic Explosivity Index (VEI) was used as a major indicator for the hazard level of pyroclastic density currents and lahars, whereby VEIs 0–3, 4–5, and ≥6 were assigned to Levels 1, 2, and 3, respectively. The maximum range of Level 1 was determined to have the dimensions of 18.10×61.61 km, Level 2, 50.83×93.78 km, and level 3, 176.39×178.64 km. For volcanic floods, four scenarios were constructed and their respective expansion ranges were established using visualization of the progressive expansion of the courses of volcanic floods between Hour 1 of the eruption onset and Day 10. The simulation performed in accordance with the configured scenarios, revealed that flood streams would pass through Erdaobaihezhen at Hour 6, Songjiangzhen and Liangjiangzhen at Hour 12, and reach Baishan Reservoir on Day 4, where they would converge. 

This research was supported by a grant ‘Development of Advanced Volcanic Disaster Response System considering Potential Volcanic Risk around Korea’ [MPSS-NH-2015-81].

  SE12-D5-PM2-P-011 (SE12-A003)
 
Near Field Ionospheric Disturbance by the Eruption of the Kelud Volcano, Indonesia, in February 2014 Observed by GNSS-TEC Method
Yuki NAKASHIMA1#+, Kosuke HEKI1, Akiko TAKEO1, Mokhamad Nur CAHYADI2, Arif ADITIYA3
1 Hokkaido University, Japan, 2 Sepuluh Nopember Institute of Technology, Indonesia, 3 Geospatial Information Agency, Indonesia
#Corresponding author: nakashima0124@frontier.hokudai.ac.jp +Presenter

The Kelud volcano, eastern part of the Java Island, Indonesia, erupted on 13 February 2014. This Plinian eruption recorded the strength 4 in the Volcanic Explosivity Index (VEI). Ionospheric wave from the eruption was detected by the Global Navigation Satellite Systems - Total Electron Contents (GNSS-TEC) method around the volcano. The ionospheric results were compared with seismic records, and the whole excitation scenario has been studied.

The raw GNSS data files in the Receiver Independent Exchange Format (RINEX) were obtained from 37 GNSS stations, and the TEC information has been extracted from them. These stations were located in the Java, the Sumatra and other small islands around the volcano, and are operated by Badan Informasi Geospatial (BIG), International GNSS Service (IGS) and Sumatra GPS Array (SuGAr).

The ionospheric oscillations were detected from slant TEC time series. They continued from 16:25 UT to 19:00 UT, and propagated as fast as ~1.0 km/s. The oscillation had frequency peaks at 3.7 mHz, 4.6 mHz, and 6.7 mHz. The former two components coincide with the two lowest atmospheric eigenfrequencies. The 6.7 mHz may correspond to one of the higher modes.

GEOFON (15 broadband seismometers; STS-1) also detected seismic waves excited by the eruption. The time series showed one Rayleigh pulse at 16:15 UT, and following continuous acoustic waves. One of the GEOFON stations, UGM, is located about 200 km away from the volcano. The seismic wave of the eruption was clear and the components with periods 200-300 sec continued from 16:25 to 19:00. It lasted ~1 hour longer than shorter period components. GSN (78 broadband seismometers; STS-2) recorded the Rayleigh wave from the erupting volcano. Their spectrogram had several clear peaks at frequencies, 3.7 mHz, 4.8 mHz, 6.7 mHz, and so on. Some of the components have been excited by atmospheric free oscillation.

These observations indicate the GNSS-TEC results detected free oscillation of the atmosphere excited by continuous Plinian eruption. This oscillation continued over an hour.

More realistic eigenfrequencies must be inferred in the future considering the atmospheric structure in the region surrounding the Kelud volcano. It must be compared with other observations, for example infrasound data or airglow, and be considered the mechanism of the excitation in detail.

  SE12-D5-PM2-P-012 (SE12-A006)
 
Gelatin, Dikes, and Fringes: Relating Analogue Dike Propagation Experiments to Interferometry Signals
Stephen PANSINO#+, Benoit TAISNE
Nanyang Technological University, Singapore
#Corresponding author: stepheng001@e.ntu.edu.sg +Presenter

Since its first use in 1994, a wealth of studies have been performed utilizing interferometry techniques (InSAR) in a variety of settings. Many geologic processes have been associated with characteristic patterns of rainbow fringes, which themselves are the result of the phase-shift between electromagnetic signals taken at different times. In this way, remote sensing techniques can be used to make inferences of subterranean processes, such as dike emplacement, that are not readily observable by the unaided eye.

In contrast, analogue experiments done in the laboratory are inherently observable and allow the capability of direct control of the experimental conditions. In the case of dike propagation experiments, large blocks of transparent gelatin are prepared and injected with a second phase, either gas or liquid. Both the gelatin and the injected fluid are well-characterized and the resulting dike is analyzed to determine its geometry and propagation dynamics, as a function of time. Experiments can be viewed using polarized light to visualize real-time stress fields occurring in the gelatin as a dike propagates through.

This study marries the extensive knowledge from each of these fields. We lab-truth characteristic interferometric patterns against laboratory experiments that represent a selection of magma migration processes. We relate stress fields, which can be viewed in cross-sectional view via analogue techniques, to surface deformation, which can be imaged via interferometric techniques.

  SE12-D5-PM2-P-013 (SE12-A010)
 
First Assessment of Marapi Plume Composition
Hilma ALFIANTI1#+, Ugan B. SAING2, Philipson BANI2
1 EOS/Center for Volcanology and Geological Hazard Mitigation, Singapore, 2 Center for Volcanology and Geological Hazard Mitigation, Indonesia
#Corresponding author: hilma_alfianti@yahoo.com +Presenter

Marapi is one of the most active volcanoes of Indonesia, located in the central part of Sumatera. At least 40 minor to moderated eruptions are reported to occur over the past century, alternately on two main crater, Tuo and Verbeek. Due to its frequent eruptive activity, the Center of Volcanology and Geological Hazard Mitigation maintains its current activity level at 2 (in the alert level scale of 1 to 4).

With the concern of better monitoring of Marapi volcanic activity and better understanding of its magmatic plumbing and degassing conditions, we carried out MultiGAS and DOAS measurement on the Verbeek crater rim, the center of present day volcanic activity.

The major volcanic gas components were quantified as follow (molar ratios): CO2/SO2 = 26 ±6, SO2/H2S = 1.8 ±0.3, H2O/CO2 = 49 ±16, H2/SO2 = 0.4 ±0.1. The mean SO2 flux is 2.6 ±0.8 ton/day.

  SE12-D5-PM2-P-014 (SE12-A012)
 
The 2014 Non-Explosive Eruption of Mayon Volcano, Philippines
Winchelle SEVILLA1#+, Mariton BORNAS2, Christian CLARITO2, April DOMINGUIANO2, Eduardo LAGUERTA2, Alejandro BALOLOY2, Helma CANON2, Arnel AQUINO2, Danilo BON2
1 Philippine Institute of Volcanology and Seismology (PHIVOLCS), Singapore, 2 Philippine Institute of Volcanology and Seismology (PHIVOLCS), Philippines
#Corresponding author: winchelle.sevilla@phivolcs.dost.gov.ph +Presenter

Mayon Volcano (13.250oN, 123.6833oE), one of 23 active volcanoes in the Philippines, exhibited a brief, non-explosive eruption that began with quiet extrusion of a ca. 40 m-high lava dome, visually observed on August 12, 2014. This was preceded by episodes of slight edifice inflation based on ground deformation data from Precise Leveling and continuous tilt monitoring and an increase in the SO2 flux from the baseline level. In contrast, seismic activity remained within background level prior to dome extrusion. Increased seismic activity only began in the morning of September 15, 2014 with a sudden spike in the number of rockfall signals and the advent of short duration, low frequency earthquakes. Crater glow due to the emission of superheated gas from the vent also become observable at night. These observations prompted the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to raise the status of Mayon to Alert Level 3 to signify that hazardous eruption could possibly occur within weeks. Evacuation of communities within the 6-km radius from the crater and within the 7-km extended zone in the southeast sector of the volcano was recommended. In the succeeding days, Mayon’s monitoring network recorded further escalation of monitored parameters. Two episodes of slow and quiet small-volume lava flow occurred, emplacing short and stubby lava lobes within 400 m of the summit vent. In this study, we present PHIVOLCS’ monitoring records of Mayon’s unrest until the lowering of its status to Alert Level 2 on December 19, 2014.

  SE12-D5-PM2-P-015 (SE12-A017)
 
Volcanic Activity at Papandayan Volcano: Monitoring and Future Research
Hetty TRIASTUTY#+, Ahmad BASUKI, Hendra GUNAWAN
Center for Volcanology and Geological Hazard Mitigation, Indonesia
#Corresponding author: htriastuty@yahoo.com +Presenter

The most devastating historical eruption of Papandayan occurred in August 1772 causing crater collapsed, destroying 40 villages and killing almost 3,000 people. Since then the activity is dominated by repeated phreatic and phreato-magmatic eruption episodes. The last eruption in November 2002 can be describe in 3 different stages: phreatic, followed by magmatic explosions, and culminated in a small directed blast ~1 km from crater.

Since 2008, volcano alert remains in level II (waspada) due to Papandayan’s seismicity level. Intermittent seismic swarms were observed in July 2011, May 2013, and October 2014 that considered being associated with regional tectonic activity. 

Several studies have been performed to better understand the Papandayan volcanic system, i.e. Earthquake mechanisms to understand magmatic processes, geomagnetic survey to map the presence of structures and geological units in the area. The influence of local tectonic activities to magmatic process that lead into Papandayan eruptive behavior, especially those which controlled the shifting of the eruptive vent, still not well understood. Our future research aim to determine the  seismic velocity structure beneath Papandayan volcano  using its seismic network. Thus, subsurface structure including deep magmatic system of Papandayan volcano and also the correlation with geolgical structure are expected to be well understood.

  SE12-D5-PM2-P-016 (SE12-A018)
 
Comparison Study Between Vault Seismometers and a New Posthole Seismometer
Stephen KILTY#+
Nanometrics, Canada
#Corresponding author: dianamartinez@nanometrics.ca +Presenter

Surface vault broadband seismometers have typically yielded good results on the vertical, but have been unreliable and noisy on the horizontal. There are several reasons for this issue, including inherent problems with surface tilt noise and thermal stability. A comparison study was undertaken between the highest performing vault seismometers and a new broadband Posthole seismometer in a downhole installation, at different depths and in various environments at stations in North America ranging from remote locations in Alaska to a noisy urban area. In the remote and urban studies, a spectral analysis was conducted and PSD plots were generated, the results of which will be provided in detail in the paper. This paper will discuss all of the results from these installations as well as the various installation techniques at these locations.

  SE12-D5-PM2-P-017 (SE12-A019)
 
Identifying Local Infrasonic Sources Using an Infrasound Array
Ritvik DOBRIYAL#+, Benoit TAISNE, Tieh-Yong KOH
Nanyang Technological University, Singapore
#Corresponding author: ritvik003@e.ntu.edu.sg +Presenter

Remote detection of volcanic explosions can give an early warning regarding potential ash injection into the atmosphere. In order to decrease the amount of false alarm, ones need to identify the local sources in order to extract with great certainty the volcanic-signal.

The present study is aimed at utilizing data gathered from an infrasound array installed in Singapore to detect and identify local infrasonic sources. The infrasound array is also used to calculate speed and direction of a moving object from the measured frequency shift due to Doppler Effect.

The infrasound array consists of five sensors, out of which data from three is available from 28th November 2014 to 11th December 2014. Three is the minimum number of sensors required to calculate sound celerity and direction of an impulsive source. Calculations are made assuming a planar wavefront traveling with a constant speed through the array. Geometry of the infrasound array and the time delay between arrivals of impulsive wave on different stations are the input needed to perform such calculation. Geometry of the array is known from the locations of the sensors, accurately estimating the time delay is therefore of primary importance.

The present study compares the time delay calculated using cross correlation of waveform with time delay calculated using spectrograms. In estimating time delay using spectrograms, effect of window size and window overlap is also studied. Shorter window size and higher overlap are found to give a better estimate. Overall, time delay estimated using cross correlation is found to be more reliable.

Continuous variation of frequency can sometimes be seen simultaneously on all three stations. Assuming it to be caused by a moving source and using Doppler Effect, the speed and location of the source of sound is estimated.

  SE13-D5-PM2-P-018 (SE13-A001)
 
Seismo-Magnetic Effect Due to Propagation Seismic Waves Through Tectonic Fault
Dmitry LOKTEV#+, Alexandeer SPIVAK
Institute of Geosphere Dynamics, Russian Academy of Sciences, Russian Federation
#Corresponding author: dloctev@idg.chph.ras.ru +Presenter

Tectonic faults have an essential influence on the forming of geophysical fields regimes [1]. Geomagnetic variations due to seismic waves propagation through the fault is of particular interest.

Influence of the fault and its zone of infection on seismo-magnetic effects is considered. Synchronous registration of seismic waves and  magnetic variations was carried out along the profile crossing the fault zone situated at the central area of the Russian platform [2]. Measurements were carried out at the different distances from the middle line of the fault in stable meteorological conditions and absence of significant magnetic perturbation and noticeable wind manifestation. Geomagnetic variations caused by seismic signals resulting from open-cast mine blasts were analyzed. It is determined that magnitude of seismo-magnetic effects decreases appreciably according to exponential law as the distance from the fault increases. It shows that the transformation of mechanical energy of vibrations into the energy of geomagnetic variations occurs more intensively in the fault. It can be connected with complex internal structure of the fault zone, also its particular fluid dynamics. Simultaneously the results of our investigations confirm that the faults with their distinctive internal structure define not only integral mechanical behaviors of the local Earth's crust areas, but complex processes connected with geophysical fields transformation and interaction. In particularly, it opens up possibilities for mapping of the active faults and estimation their properties on the base of the analysis of peculiarities of spatial and temporal variations of the geophysical fields.

[1] A.A. Spivak. The specific features of geophysical fields in the fault zones. Izvestiya, Physics of the Solid Earth. 2010. Vol. 46. No. 4. P. 327-338.

[2] V.V. Adushkin, A.A. Spivak, V.A. Kharlamov. Peculiarities of the seismic magnetic effect in the zone of fracture influence. Doklady Earth Science. 2014. Vol. 454. Part 2. P. 185-188.

  SE13-D5-PM2-P-019 (SE13-A004)
 
Deep Structure and Onshore-Offshore Tectonic Evolution of the Central-East Indian Margin : Insight from Multichannel Seismic and Potential Field Data
Gangumalla SRINIVASA RAO1#+, Pranaya SANGVAI2, Radhakrishna MUNUKUTLA1, K.S.R. MURTHY3
1 Indian Institute of Technology Bombay, India, 2 Reliance Industries Ltd, India, 3 National Institute of Oceanography, India
#Corresponding author: vasugeos@gmail.com +Presenter

The Eastern continental margin of India (ECMI) is a passive margin formed as a consequence of double breakup events between India, Elan Bank and the Eastern Antarctica. The margin is characterized by the presence of severalperi-cratonic rift basins such as the Cauvery, Palar, KrishnaGodavari (K-G), Mahanadi,and Bengal basins. Here, we present the results of an integrated analysis of gravity and magnetic data along with multichannel seismic reflection data in the non-basinal area of the ECMI that lies between K-G and Mahanadi basins in order to delineate the crustal configuration and the offshore structural continuity. The composite magnetic anomaly map of the region has revealed a high amplitude coast parallel magnetic anomaly pattern (800-1000 nT) in the offshore SW of Chilka Lake. Image enhancedmaps of gravity and magnetic data at the margin revealed i) a linear trend of rift related dyke intrusions over the inner part of shelf SW of Chilka Lake, ii) horst-graben configuration of the continental basement with predominantly NE-SW trend, iii) offshore extension of a NW-SE trend (Vamsadhara Trend) located off Srikakulam to Kalingapatnam, iv) the N-S 85°E trend abductting the shelf at the Chilka Lake. Multichannel seismic reflection (MCS) data and the isopach maps for the major depositional sequences indicate thinning of sediments between Visakhapatnam and Gopalpurwith influx of deltaic sediments in the northern and southern parts by the Mahanadi and Godavari rivers respectively. More importantly, the MCS data reveals a major folding in the Cenozoic sedimentary strata at the foot of the continental slope and the rift related host-graben structures in the basement. The crustal models derived from the joint interpretation of gravity and magnetic data further indicated thinning of the crust and nature of continent-ocean crustal transition zone at the margin. Tectonic implications of the above investigation have been discussed in this paper.

  SE13-D5-PM2-P-020 (SE13-A007)
 
Azimuth Verification of the MeSO-Net Accelerographs ~Towards the Imaging of Ground Motions in the Tokyo Metropolitan Area ~
Masayuki KANO1#+, Hiromichi NAGAO1, Katsuhiko SHIOMI2, Shin'ichi SAKAI1, Shigeki NAKAGAWA1, Sadanobu MIZUSAKO1, Muneo HORI1, Naoshi HIRATA1
1 The University of Tokyo, Japan, 2 National Research Institute for Earth Science and Disaster Prevention, Japan
#Corresponding author: kano@eri.u-tokyo.ac.jp +Presenter

In the Tokyo metropolitan area of Japan, large plate boundary earthquakes repeatedly occurred with intervals ranging from 200 to 400 years in the case of M 8 class, and with an interval of approximately 27.5 years in the case of M 7 class. Rapid prediction of damages on constructions due to such a large earthquake is important to quickly decide the priority order in recovery actions without waiting for on-site reports. Such a rapid prediction system requires an image of ground motion in the target area as an input, which is to be estimated from seismograms of dense seismological observation networks. A dense seismic array “MeSO-net” (Metropolitan Seismic Observation network), in which 296 accelerometers are installed with several kilometer intervals, was established in 2007 for the purpose of the disaster mitigation for forthcoming large earthquakes. Whether the actual azimuths of MeSO-net seismometers newly installed after 2009 were really in the magnetic north or not have not been verified yet, while the azimuths of three of the seismometers installed before 2008 were already confirmed to be in the opposite direction. Since such obvious errors in the azimuths badly affect subsequent data processing, we evaluate the azimuths of all seismometers based on the cross-correlation with seismograms recorded at nearby Hi-net tiltmeters and F-net broadband seismometers. Our result suggest that the northward components at more than 80 % of stations are determined to be within 10 degrees from the magnetic north, while those at the three stations are reconfirmed to rotate more than 90 degrees as the previous study pointed out.

  SE13-D5-PM2-P-021 (SE13-A008)
 
Acoustic Emission Generation by Lightning Discharge
Sergey SMIRNOV#+, Yury MARAPULETS
Institute of Cosmophysical Research and Radio Wave Propagation of the Far-Eastern Branch of Russian Academy of Science (IKIR FEB RAS), Russian Federation
#Corresponding author: kamtalker@gmail.com +Presenter

The peculiarity of atmosphere electric state in Kamchatka is a small number of lightning storms. On October 2, 2008 a unique for this place event occurred. At 17:46 LT (4:46 UTC) a single lightning discharge, not accompanied by precipitation, occurred. A reaction to this discharge in electric field and in acoustic emission was recorded at “Paratunka” observatory. The effect of a single lightning on electric field intensity in the near ground atmosphere was investigated. The effect appeared as a sharp decrease of electric field potential gradient value from 80 V/m to minus 21 V/m. The intensity recovery process is described by a plane capacitor model with the characteristic recovery time of 17 s. Acoustic emission registration was carried out by a hydro-acoustic receiver (hydrophone) with the sensitivity together with a buit-in pre-amplifier of the order of hundreds of mV/Pa. Application of a hydrophone in a basin allowed us to register geoacoustic signal in the range 0.1 Hz - 11 kHz, which is significantly bigger than that of a usual seismometer. Simultaneously with the electric field, acoustic emission response on lightning discharge was registered. The signal directly from the discharge was registered in the highest range of 6.5 - 11 kHz and the following sound wave was observed in all channels.

Smirnov, S. E. and Marapulets, Y. V.: Influence of a single lightning discharge on the intensity of an air electric field and acoustic emission of near-surface rocks, Solid Earth, 3, 307-311, doi:10.5194/se-3-307-2012, 2012.

  SE13-D5-PM2-P-022 (SE13-A009)
 
Using Ichnofossil to Determine Reservoir Deposit in the Deltaic Setting of Balikpapan Formation, Samarinda, East Kalimantan, Indonesia
Aswan ASWAN#+
Institute of Technology Bandung (ITB), Indonesia
#Corresponding author: aswan_gl@gc.itb.ac.id +Presenter

Determination of the delta system parts deposit is often difficult if observed on a small dimensions outcrops or core. This study identified the content of trace fossils in the delta system parts deposit based on an ideal outcrop. Ichnofossils study will be very helpful in determining of the reservoir thickness based on core analysis, especially in case of delta system changes without significant lithologic changes. This research was conducted in the Mahakam River delta sediments of Balikpapan Formation in Samarinda city and surounding, East Kalimantan, Indonesia. Integrated ichnofossils paleontological and sedimentological observation reveals that Balikpapan Formation around Samarinda is composed of at least 3 (three) ichnofossils association that reflect their part of delta system. The lower part of Balikpapan Formation located at the Kunjang River and surrounding area known as transition area between fluvial channel and delta, characterized by thick sandstone and shale with the presence of Asterosoma, Rosselia, and Arenicolites trace fossils association. The middle part of Balikpapan Formation around Medical Center location and surrounding, characterized by intercalation between sandstone, shale and coal as well as the presence of small amounts and small size Diplocraterion, Ophiomorpha and Asterosoma. This part always interpreted by the previous authors as prograding delta front mouth bar deposit. The upper part of Balikpapan Formation crops out around Stadion Utama, characterized by the continuously sandstone, shale, and coal intercalation was believed as top delta front mouthbar sediment deposited in the open sea environment. This study signed this unit content of Teichicnus, Gyrolithes, Skolithos, Asterosoma, and Zoophycus ichnofossils association.

  SE13-D5-PM2-P-023 (SE13-A010)
 
Several Basin's Amplification Effect on Ground Motion During the Period of 2~10 Second
Changhua FU#+, Mengtan GAO
Institute of Geophysics, China Earthquake Administration, China
#Corresponding author: fuchanghua2004@163.com +Presenter

A lot of high-rise buildings are located in basins. However, history tells us that the intensity of long-period ground motion in basin is usually larger than that in its vicinities when a strong earthquake occurs. This higher intensity will cause severe damage to high-rise buildings and other structures which have long self-vibrating periods. So, studying basin amplification effect on long-period ground motion is essential to seismic fortification of high-rise buildings. Because it helps us to understand reasonable seismic fortification requirement of high-rise building in basins, and provide scientific reference for city future planning, earthquake emergency and rescue.

Here, we selected several actual basins as researching objects, such as Yuxi Basin (smaller scale, in Yunnan province, China), Taiyuan Basin and Beijing Basin (larger scale, in Shanxi province and Beijing city, China, respectively), and used ground motion simulation (GMS) method to study basin amplification effect on ground motion during the period of 2~10 second. For each basin, based on its seismotectonic background, several scenario earthquakes were set up. Then, velocity time histories of long-period ground motion under special scenario earthquake in every basin were acquired by GMS. Subsequently, we converted the velocity time history to acceleration response spectrum within 2~10 second periods, and computed basin amplification factor of acceleration response spectrum. Finally, through regression analysis, the basin amplification effect on long-period ground motion was analyzed. The results are as follows: 1. Basin amplification factor of acceleration response spectrum is mainly affected by sedimentary thickness and period, the amplification factor increases with equivalent sedimentary thickness (consisting of thicknesses of Quaternary system and Tertiary system), but decreases with period. They are satisfied with binomial distribution function; 2.Basin amplification factor on fault-parallel component are usually larger than that on fault-perpendicular component; 3. Although the three basins are of different scales, they have similar phenomenon.

  SE13-D5-PM2-P-024 (SE13-A011)
 
A New Reliable Real-Time Source Inversion System in Taiwan: Auto BATS CMT Solution
Wen-Hui LEE1+, Wen-Tzong LIANG1#, Pei-Ru JIAN2, Tai-Lin TSENG2
1 Academia Sinica, Taiwan, 2 National Taiwan University, Taiwan
#Corresponding author: wtl@earth.sinica.edu.tw +Presenter

We have applied a new source inversion technique to the Broadband Array in Taiwan for Seismology to obtain a real-time and reliable focal mechanism solution (Auto BATS CMT) for felt earthquakes occurred in the Taiwan region. This system is triggered by the earthquake alert issued by the Central Weather Bureau of Taiwan. It starts with automated extraction of high quality waveforms and then perform source inversions with various criteria on station selection, frequency band, velocity model and percent limitation of isotropic component. Waveform data with low signal-to-noise ratio is discarded automatically during the stage of data preparation. In total there are 108 solutions with different combinations of criteria for one single event. By exploring the solutions, we are able to evaluate the reliability of the optimum solution, whose misfit is the lowest, and the spread of parameters such as strike, dip, slip, and focal depth. It seems that the reliability of CMT solution can be best described by the spread of Kagan's angle between each solution pair and its mean value. In the past 2 years, we have obtained more than 170 earthquake solutions automatically through this system with Mw ranging between 2.8 and 6.2. Almost 80% of the Kagan's angle between Auto- and manual-BATS CMT solutions is smaller than 35º, implying that they are generally consistent with each other. After triggering, the whole procedure takes less than 5 minutes to pursue a reliable solution for one single event. This system is now accessible online at http://tecdc.earth.sinica.edu.tw/FM/.

  SE13-D5-PM2-P-025 (SE13-A014)
 
Reconsideration of Pemali Formation as Source Rock of Banyumas Basin’s Petroleum System, Central Jawa, Indonesia Based on New Age Re-identification
Aswan ASWAN1#+, Khoiril MARYUNANI1, Arif HANIF HIDAYAT2, M. Adib SINTO BASKORO1, Yan ANDRIANSYAH KABUL3
1 Institute of Technology Bandung (ITB), Indonesia, 2 PT. Mahakam Sumber Jaya, Indonesia, 3 PT. Bukit Mandiri Utama, Indonesia
#Corresponding author: aswan_gl@gc.itb.ac.id +Presenter

Pemali Formation of Central Jawa Indonesia regarded as the source rock in respect to the Banyumas Basin’s Petroleum System. The following study of Pemali Formation that ever done around Bobotsari Sub-basin (part of Banyumas Basin) concluded that Pemali Formation’s age is much younger than previously known. The Pemali Formation was originally interpreted as “Oligo-Miocene”, but is now shown to be late Miocene to early Pliocene. The previous older age intrepreted due to the reworked fossils content that also reported in the following study. Mio-Pliocene tectonic influenced during sedimentation in the Bobotsari Sub-basin was regarded as responsible for the content of the reworked fossils. The new much younger age of Pemali Formation is of course also changed the petroleum system understanding around this area. The present study tried to confirm the age of the rock units which considered as equivalent to Pemali Formation that collected from the area outside of Bobotsari Sub-basin. Pemali Formation’s age determination in this study is based on samples taken from the fields of Kuningan area (NW of the Bobotsari Sub-basin), Lumbir area (SW of the Bobotsari Sub-basin) and Merawu (NE of the Bobotsari Sub-basin). Age analysis from the first two locations is late Miocene-early Pliocene (N16-N18) and signed an equivalent age with Pemali Formation from Bobotsari Sub-basin. Samples taken from Merawu Formation (which is considered equivalent to Pemali Formation) in the Merawu area reveals slightly older age of late Miocene. The lower part of the Merawu Formation shows the age of “not older than middle Miocene” based on the presence Hastigerina siphonifera (N12-Recent), and the upper part signed the late Miocene age (N16-N17) based on the dominant sinistral shell of Globorotalia menardii presence as index foraminifer. Based on geochemical data and the new more regional age determination, oil seeps from Pemali Formation are considered mainly supplied by the older sediment sources (Paleogene sources?) rather than Neogene of Pemali Formation sources.

  SE13-D5-PM2-P-026 (SE13-A020)
 
Simulating the Shallow Soil Response by Numerical Modeling of Wave Propagation in the Western Plain of Taiwan
Chun-Te CHEN1#+, Chun-Hsiang KUO2, Kuo-Liang WEN3, Che-Min LIN2
1 Academia Sinica, Taiwan, 2 National Center for Research on Earthquake Engineering, National Applied Research Laboratories, Taiwan, 3 National Central University, Taiwan
#Corresponding author: pokayoke69@gmail.com +Presenter

The shallow S-wave velocity structures of the western plain of Taiwan were estimated by forty-five microtremor array measurements. We assumed the S-wave velocity of the engineering bedrock to be 600 m/s; the depths of the substructure are between 5m and 338m gradually increasing from eastern foot of mountain to western coastline. The results of very shallow part are in good agreement with the suspension PS-logging (EGDT, Engineering Geological Database for TSMIP) data. The pattern of the depth contour is also corresponding with the geological and the geophysical information. Complete 3D velocity model was constructed with three subsurface structures and 3D tomography velocity structure, where the velocity is constant in each subsurface. We apply 3D Finite-Difference modeling of scenario earthquakes wave propagation to calculating the shallow soil response. The larger modeling site amplification effects and wave propagation behavior compare to without shallow subsurface results. The high resolution shallow substructure was suggest use to construct with the 3D tomography velocity structure so as to improve the modeling of wave propagation and seismic hazard analysis.

  SE13-D5-PM2-P-027 (SE13-A021)
 
From Seismic Waveforms to Seismic Wavefield: A Feasibility Study of the Seismic Gradiometry Applied to the Hi-Net Array
Takuto MAEDA#+, Kiwamu NISHIDA, Ryota TAKAGI, Kazushige OBARA
The University of Tokyo, Japan
#Corresponding author: maeda@eri.u-tokyo.ac.jp +Presenter

The high-sensitive seismograph network (Hi-net) operated by NIED, Japan has nearly 800 stations with average separation of 20 km. Although it was designed for high-frequency seismic waves, it also acts as a long-period seismograph array because of the wide dynamic range and high S/N. In such a long-period band, dense data may be treated as 2D wavefield rather than independent seismic wave traces. In this study, we attempted to assess the seismic wavefield by applying seismic gradiometry (hereafter referred to as SG) to Hi-net.

The SG first estimates the wave amplitude and its spatial derivatives from station records by the Taylor series approximation. We applied it to a synthetic dataset at the actual Hi-net station layout. The synthetic data have wavespeed of 3 km/s with geometrical spreading and radiation pattern. At equally spaced grid points, the wave amplitude and spatial derivatives are estimated by using stations whose distance is shorter than 50 km. Comparing with the analytic solution, it was found that the wavefield and the derivatives are well estimated with maximum relative errors of about 5% and 10%, respectively. The slowness vector, the radiation pattern and the geometrical spreading are estimated by estimated wavefield and spatial derivatives. The estimated slowness vector well matched to the assumptions, and the radiation pattern shows significant variation at around the null axis as expected.

Our preliminarily results show that the SG well suite to the Hi-net seismograph to extract wavefield behavior at the long periods. This method is appealing that it can estimate the slowness at spatially homogeneous grid, and that it can extract amplitude variation such as radiation pattern. It is promising to obtain phase velocity variation from direct waves, and to grasp wave packets originated from scattering from coda, by applying the SG to Hi-net dense array data.

  SE13-D5-PM2-P-028 (SE13-A023)
 
Teleseismic Similar Earthquakes Detected by the Seismic Observation Network in Japan
Toshihiro IGARASHI#+
Earthquake Research Institute, The University of Tokyo, Japan
#Corresponding author: igarashi@eri.u-tokyo.ac.jp +Presenter

Recently, there are found many sequences of similar earthquakes which are caused by repeating slips of small patches surrounded by aseismic slip areas at plate boundary zones such as California, Taiwan, and Japan. In this study, I detected similar earthquakes which occurred in the world by calculating cross-correlation coefficients of band-pass filtering seismograms, and investigated the spatial distributions and temporal changes. I analyzed teleseismic waveform data observed in the seismic observation network in Japan for about 13 years from August 2002. Four pass-band filters with 0.1-0.5 Hz, 0.2-1.0 Hz, 0.5-1.0 Hz, and 1.0-4.0 Hz are used for this calculation. The time window is 80 seconds including the direct P-wave. As a result, I found many sequences of similar earthquakes in the Sumatra and Tonga subduction zones. Sequences of similar earthquakes with the highest cross correlation coefficients were detected in an aftershock area of the 2004 Sumatra earthquake. If I apply the scaling relations among a seismic scalar moment, recurrence interval, and slip-rate, which are found in California and Taiwan, to these sequences, the slip-rates in these areas are higher than 10 cm per year. The fast slip-rates correspond to the postseismic slip after the 2004 Sumatra earthquake and the high-velocity relative plate motion in the Tonga subduction zone, and probably indicate the space-time changes of inter-plate aseismic slips. I believe that I am likely to detect more similar earthquakes by extending analysis periods in the area where they were not found in this analysis. The database of global similar earthquakes enables the comparison of the inter-plate slip-rates of the world. Furthermore they will be useful for extracting information on space-time changes of the seismic velocity structures beneath the seismic observation networks.

  SE13-D5-PM2-P-029 (SE13-A030)
 
The Application of Ground-Based LIDAR Techniques to the Study of Foliated Rock Tunnel Deformation
Kuo YUAN+, Tai Tien WANG, Wei LO#
National Taipei University of Technology, Taiwan
#Corresponding author: lowei93@ntut.edu.tw +Presenter

The construction of Guanin Tunnel, Which in the project of Suhua improvements is located in Ilan-Hualian, eastern Taiwan. The rock stratigraphic unit along the Guanin tunnel is Wuta formation (Lin et al., 1990) mainly composed of mica schist, quartz-mica schist, chlorite schist, marble and siliceous schist. Main foliation are approximately N60W-N80E, and dips are approximately 40-60 degrees toward north. There are 2-3 sets of joints can be observed.

Ground-based LIDAR provides an advantage to understand the early deformation stage of a tunnel that after excavation of each cycle, in contrast to traditional 3d monitoring method. Ground-based LIDAR could monitor the deformation before lattice girdler and shotcrete being accomplished.

The deformation behavior of foliated rock is more complicated than the deformation behavior of non-foliated rocks. According to the field observation and study, there are seven important factors would affect early stage of foliated-rock deformation include : 1. discontinuous density, 2. amounts of Joint sets and their attitudes, 3. width and attitudes of shear zones, 4. rock material anisotropy, 5. strength of rock material, 6. ground water condition, and 7. the attitudes of minor fold axis.

  SE13-D5-PM2-P-030 (SE13-A031)
 
Mineral Equilibrium Modeling and Geothermometry of the Pre-1991 Eruption Mount Pinatubo Exploratory Well Fluids
John Paul MENDOZA1#+, Maria Ines Rosana BALANGUE2, Carlo ARCILLA1
1 University of the Philippines Diliman, Philippines, 2 University of the Philippines, Philippines
#Corresponding author: jpmendoza23@yahoo.com +Presenter

The equilibrium state between the present-day geothermal fluids and hydrothermal mineral phases of the pre-1991 eruption Mount Pinatubo exploratory wells were tested using the program Geochemist’s Workbench 10.0.3. A technique employed by Reed and Spycher (1984) uses mineral saturation indices or log (Q/K) of different species (where Q is the ion activity product or reaction quotient and K is the equilibrium constant) over a range of temperature to determine mineral equilibria. Molecular ratios of both fluid and gases were also used to characterize the geothermal system.

Well fluids range from immature to partially equilibrated (Giggenbach, 1988). Temperature of 240°C for PN-1 and 300-340°C for PN-2D and –3D were obtained using Na-K-Mg geothermometers. PIN-2D is the least mixed water (having uniform Cl/B) that is nearest the magmatic upflow characterized by low Cl/SO4, high Mg, low pH and being the nearest to the pre-eruption caldera. Magmatic input was confirmed using CO2/N2 gas ratio comparable with White Island and some Japanese volcanoes. Mineral saturation indices (log Q/K) were calculated from 20° to 300°C revealing a neutral-pH alteration assemblage consisting of pyrite, amorphous silica, chalcedony, cristobalite, quartz, tridymite, dolomite, talc (at >280° C for PIN-2D), calcite (for PIN-3D), huntite, pyrrhotite and pyrite. Only PIN-2D exhibited covergence at 245°C consistent with the molecular geothermometers. Undersaturation of some clay minerals and pyroxene and the absence of important clay geothermometers supported by the disconvergence of the mineral saturation plots for most wells suggests that the present day hydrothermal fluids is not in equilibrium with the hydrothermal mineral phases.

  SE13-D5-PM2-P-031 (SE13-A034)
 
Geometry and Pore Pressure Shape the Period-Multiplying Tremors on the Deep San Andreas Fault
Deepa MELE VEEDU#+, Sylvain BARBOT
Earth Observatory of Singapore, Nanyang Technological University, Singapore
#Corresponding author: deepa004@e.ntu.edu.sg +Presenter

Observations of tectonic tremors and their association to aseismic slip challenge our understanding of the dynamics of faulting. In particular, the long record of tremors on the deep San Andreas Fault near Parkfield, with its complex pattern of doublings and halvings of recurrence times still eludes explanations. The tremor pattern was regularly oscillating with period doublings and halvings of 3 and 6 days from mid-2003 until it was disrupted by the 2004 Mw 6.0 Parkfield earthquake. But by the end of 2007, the previous pattern resumed.

Here, we show that a single asperity with homogenous frictional properties can produce different faulting mechanisms in the same area in a single simulation. Our three-dimensional model is based on rate-and-state friction with a single velocity-weakening patch embedded in a velocity-strengthening region. Non-circular asperities may produce an alternating sequence of slow-slip events and regular earthquakes under a certain range of geometrical and frictional properties in a wider stability range than circular asperities.

We use these findings to explain the period doubling recurrence times of deep tectonic tremors on the San Andreas Fault. We assume that the tremors are due to slip on micro-asperities triggered by slow-slip events and earthquakes alike in a single, much larger asperity. We simulated the tremor sequence of about 2000 slip events in a self-consistent model assuming that the postseismic transient is caused by effective pore-pressure variations. Our event duration is in the range of 25 to 150 seconds, closely comparable to that of a typical Parkfield tectonic tremor.

Our results illustrate the importance of aseismic processes in the history of fault slip evolution. If slow-slip events precede destructive main shocks, they may provide the key observations to improve earthquake forecast. Better understanding of the mechanics of slow-slip events will be paramount to turn observations into useful earthquake warnings.

  SE13-D5-PM2-P-032 (SE13-A035)
 
Evaluation of Temporal Variation in Earthquake Detectability with Time-Dependent Smoothness Constraint
Takaki IWATA#+
Tokiwa University, Japan
#Corresponding author: tiwata@tokiwa.ac.jp +Presenter

Assessing the earthquake detectability is vital in analyses of seismicity. In the assessment, we should note that the detectability usually has a temporal variation; therefore, evaluating the temporal variation is indispensable for the precise assessment of the detectability. Ogata and Katsura (1993, GJI) proposed a Bayesian approach for the evaluation. In this approach, the temporal variation in a model parameter quantifying the detectability is estimated with a spline approximation of the parameter and smoothness constraint.

In previous studies which exploit this approach (e.g., Ogata & Katsura, 2006, GRL; Iwata, 2008, GJI; 2013 GJI; 2014, Aust. New Zealand J. Stat.; Iwata and Kanao, 2015, Polar Science; Omi et al., 2013, Sci. Rep.), the strength of the smoothness constraint is assumed to be constant in time. However, this assumption is questionable if a seismicity rate is not constant, because, in such a case, the amount of the information or data varies in time, resulting in a biased estimation of the temporal variation in the parameter.

To mitigate the bias, this study suggests a Bayesian estimation with time-dependent smoothness constraint. The suggestion is examined in a following numerical simulation. As a typical example of inconstant occurrence rate, aftershock sequences with the Omori-Utsu decay and an appropriate temporal variation in earthquake detectability are artificially generated. The suggested method is implemented with a sequential Monte Carlo algorithm (or particle filter), and is applied to 100 generated sequences. In the analysis with constant smoothness constraint, the mean of the estimates of the temporal variation in the model parameter systematically deviates from the assumed detectability for the 100 sequences over a study period whereas the deviation occurs only in an early stage of the study period in the analysis with time-dependent smoothness constraint; the suggested method is effective to improve the bias of the estimation.

  SE13-D5-PM2-P-033 (SE13-A036)
 
Evolution of AE Source Parameters Associated with Large Frictional Sliding Distance
Yasuo YABE#+, Hiroo TSUDA, Takuro IIDA, Shuhei ABE
Tohoku University, Japan
#Corresponding author: yasuo.yabe.e2@tohoku.ac.jp +Presenter

We have performed laboratory experiments to investigate evolution of a frictional property of a fault associated with accumulation of sliding distances up to ~80 mm. Frictional property of a middle grain granite under a constant normal stress of 5-15 MPa was the velocity strengthening (a-b>0 in the rate and state friction law) at the beginning of experiments. The value of a-b gradually decreased with sliding to negative (velocity weakening). Then, it took a constant negative value, when the sliding distance reached a critical distance. This evolution could be approximated by an exponential function with a characteristic sliding distance, dc. The m-value of AE activity on the fault showed the evolution similar to the frictional property. The sliding distance dependence of the m-value, which increased with sliding to a constant value, could be approximated by the exponential function with the same characteristic sliding distance as that of the frictional property. To elucidate underlying physics of these simultaneous evolutions, we evaluated evolution of source parameters of AE events on the faults.

The source radius and the stress drop were estimated from the rise time, the pulse width, and the maximum amplitude of the P-wave first arrival observed by a board band AE sensor. The source radius little depended on the sliding distance. At a small sliding distance, the stress drop was large on average with large standard deviation. The average and the standard deviation of the stress drop decreased with sliding. Then, the average stress drop took a constant value, when the sliding distance reached the same critical distance dc as the evolution of frictional property. Considering this with change in fault surface topographies during sliding, these evolutions can be interpreted to be caused by change in micro mechanics of contacts between fault surfaces from interlocking to welding.

  SE13-D5-PM2-P-034 (SE13-A042)
 
Slow Slip Events Detected Using an Array of Extensometers
Yasuyuki KANO#+, Yoshinobu HOSO, Kensuke ONOUE
Kyoto University, Japan
#Corresponding author: kano@rcep.dpri.kyoto-u.ac.jp +Presenter

Crustal deformations associated with slow slip events occurring below the Kii peninsula and Shikoku have been observed. An array consists of two traditional extensometers and two short-span extensometers detects several episode of the strain changes. The array observation was implemented by short-span extensometer with 1.5 m-long standard measure. Some of the episode occurred at the area surrounded by the array. The array which provides detailed analyses of episodic tremor and slip.

The short-span extensometers are installed at Nakaheji and Mizunomi which is located at western part of the Kii peninsula. Since the commercial power supply is not available at Mizunomi site, we developed observation system for short-span extensometers with solar cells. The system can reduce the noise arise from commercial power supply, which compensate the shortage of resolution of the short-span extensometer.

The array observation contributes to improve the detection capability of crustal deformation by eliminating noise caused by weather disturbance and to have better understanding of slow slip events such as slip distribution.

  SE13-D5-PM2-P-035 (SE13-A043)
 
An Analysis of Tradeoffs Between Seismometer Performance and Convenience
Stephen KILTY#+
Nanometrics, Canada
#Corresponding author: dianamartinez@nanometrics.ca +Presenter

In recent years, a multitude of different broadband seismometers of varying periods and performance specifications have been developed. Scientists often have the unenviable task of selecting the best equipment to suit a broad range of applications. We provide a high level view of some of the tradeoffs available to the sensor design team that directly impact the utility and cost of the final product. Additionally we review costs related to network installation, maintenance and operation and investigate how these can be influenced by instrument choice. We compare the low noise model, the high noise model, and the site noise of a typical installation to the expected signal strength for a variety of case studies ranging from teleseismic to microseismic settings. For each case study we determine the effective passband, the frequency range in which the expected signal exceeds both the site and instrument noise. We compare the effective passband of a number of different instruments and investigate the effects of changes to both instrument and site noise on the size of the passband. We find that for typical installations, the site noise has the largest influence on the effective passband of an instrument. We demonstrate that in some circumstances tradeoffs in certain performance specifications can pay dividends in ease and cost of deployment without compromising overall network performance.

  SE13-D5-PM2-P-036 (SE13-A045)
 
The High Frequency Spectral Decay Parameter Kappa in Taiwan
Shun Chiang CHANG#+, Kuo-Liang WEN
National Central University, Taiwan
#Corresponding author: fcuiii@gmail.com +Presenter

High frequency attenuation parameter kappa(κ) was analyzed by spectral fitting method(Anderson and Hough,1984) from the TSMIP(Taiwan Strong Motion Instrumentation Program) strong motion observation data. From the S-wave spectrum of each event recorded by the same station, the spectral attenuation parameter kappa can be calculated from the amplitude decay with respect to frequency. Then based on the each event’s hypocentral distance(R) and kappa, we can generate the relationship between κ and R. κ0 (κ at R=0) can be referred as one of the site factors. In this study,17202 earthquake records from 1993 to 2012 with 10~150 km hypocentral distance and focal depth smaller than 30 km that recorded by 431 TSMIP strong motion stations are analyzed to calculated the kappa for each station. Due to 294 TSMIP stations selected in this study had Vs30 information from logging measurement (Kuo et al.,2012),the relationship between κ0 and Vs30 can be obtained. In average, κ0 for site classes B is 0.044, C is 0.056, D is 0.065, and E is 0.076 respectively. The κ0 for site class A is 0.034 but it only from the earthquake records of one station due to only TSMIP station was classified as category A.

Keywords: Kappa, TSMIP, Vs30.

  SE13-D5-PM2-P-037 (SE13-A047)
 
The Variation of Crustal Structure Along the Song Ma Shear Zone, Northern Vietnam
Chien-Min SU1#+, Strong WEN2, Chi-Chia TANG3, Yu-Lien YEH1, Chau-Huei CHEN1
1 National Chung Cheng University, Taiwan, 2 National Center for Research on Earthquake Engineering, Taiwan, 3 China University of Geosciences, China
#Corresponding author: savesola@gmail.com +Presenter

The Northern Vietnam is divided into two regions by the strike-slip Red River Shear Zone (RRSZ), which the southwestern part belongs to the Indochina block and the northeastern is a portion of the South China block with distinct characteristics geologically. From previous studies, the Red River fault is a well-known strike-slip fault and it plays an important role in gaining the tectonic evolution of the extrusion process in the Indochina, which is caused by the vigorous collision between the India and Eurasia plates. Although metamorphosed rocks have been found at the Song Ma Shear Zone (SMSZ) from geological survey and several studies have supported that SMSZ is characterized a subduction zone system and possibly a boundary between the South China and Indochina plates based on this finding. However, the above argument whether the SMSZ is a subduction zone of South China and Indochina plates or not, and its relation to the tectonic evolution in northern Vietnam is still in debating. In this study, we intend to investigate the variations of Moho depth along the SMSZ, which can provide critical information for understanding the tectonic evolution process in this area. We also applied the common conversion point (CCP) stacking method to teleseismic converted wave that is very useful to image the crustal structure along a linear array and identify whether the fault block extends through the entire crust. Therefore, we selected two depth profiles along the SMSZ for imaging lateral variations of impedance from stacking, and our preliminary results indicate that the variation in depth of the Moho discontinuity beneath the SMSZ is between 25 km and 35 km and the fault structure also can be identified from the CCP image.

  SE13-D5-PM2-P-038 (SE13-A048)
 
The Study of Non-Double-Couple Earthquakes in the Ma River Fault Zone, Vietnam
Wei-Jhe WU1#+, Strong WEN2, Chi-Chia TANG3, Yu-Lien YEH1, Chau-Huei CHEN1
1 National Chung Cheng University, Taiwan, 2 National Center for Research on Earthquake Engineering, Taiwan, 3 China University of Geosciences, China
#Corresponding author: brucezmc@yahoo.com.tw +Presenter

Most studies support that focal mechanisms of most earthquakes caused by shear motion on planar faults fall into the double-couple (DC) regime. However, this is not always true for seismic events with non-shear motion, such as earthquakes occur in geothermal and volcanic areas, which have been reported with non-double-couple (non-DC) mechanisms. Previous results also indicate that non-DC sources are types of earthquake rupture associated with complicated fault geometry and compositions. Understanding non-DC earthquakes is crucial for getting detailed insights on faulting process and tectonic evolution. The major object of this research is to investigate the non-DC focal mechanism as well as source rupture process of earthquakes in Ma River shear zone, northern Vietnam. Due to the Ma river shear zone plays an important role in understanding the tectonic evolution between the Indian plate and the Eurasian plate, the study of faulting mechanisms in the plate boundary area is necessarily. Our results indicate that the non-DC components in seismic moment tensor control the rupture behavior in microearthquakes, and this may be caused by geothermal alteration or fluid flows into newly formed cracks, which leads to partial compensation of the volumetric component. Thus, the derived source parameters obtained from this study can serve as a detail physical status (such as fluid migration, fault geometry, the pressure of the leading edge of the rupturing) to investigate the seismongenic structures beneath the fault zone for future research.

  SE16-D5-AM2-326-008 (SE16-A022)
 
Geochronology and Geochemistry of Igneous Rocks from Dazhou Island in the Hainan Island, South China
Quanshu YAN#+, Zhihua CHEN, Xuefa SHI
First Institute of Oceanography, State Oceanic Administration, China
#Corresponding author: yanquanshu@163.com +Presenter

This study presents zircon U-Pb ages and geochemistry of granites and basic diabase veins in Dazhou Island located 5 km southeast of Hainan Island. The age for granites is 237.2Ma (MSWD=0.14, n=14), suggesting that they were emplaced in the late middle Triassic and are products of magmatic (thermal)-tectonic episodes during the closure of paleo-Tethys. The granites belong to the shoshonitic magmatic series and are metaluminous I-type granites. They are systematically depleted in Ba, Nb, Sr, P, and Ti, and have variable ranges of initial 87Sr/86Sr ratios (0.71005~0.71110), but relatively constant εNd(t) values (-6.4~ -6.8). The two-stage depleted mantle Nd model ages (TDM2=1531-1562Ma) for these granites suggest that they may have originated from partial melting of the lower crust with a crustal residence age of early Middle Proterozoic Era. The zircon U-Pb ages for diabase veins can be divided into three groups. The age for Group I is 236.8Ma (n=4), which represents the crystallization age of the veins and somewhat younger than the accompanying granites. The ages for Group II and III are 1767 Ma (n=6) and 2432 Ma (n=3), respectively. These suggest that the veins have inherited some old zircons that possibly represent old geological events in the Hainan Islands. The diabase also belongs to the shoshonitic magmatic series and has arc-like trace element characteristics. The veins have high 87Sr/86Sr and low 143Nd/144Nd isotopic compositions, which suggest that they may have originated from an enriched mantle II type source or a mantle source metasomatized by aqueous fluids released from previously subducted slab. The new ages obtained for the Dazhou igneous rocks in the present study are similar to those for the Qiongzhou batholith in the Hainan Island, which implies that the Hainan Island had also regionally experienced a middle Triassic extension event after the Indosinian compressional/orogenic period.

  SE16-D5-PM2-P-014 (SE16-A003)
 
Aqueous Fluid Immiscibility from a Porphyry-Type Breccia-Pipe Copper Deposit in the Gyeongsang Basin, South Korea
Minyoung SEO+, Yonghoon WOO, Hyungsuk KIM, Kyounghee YANG#
Pusan National University, South Korea
#Corresponding author: yangkyhe@pusan.ac.kr +Presenter

Small porphyry-type breccia-pipe copper (Cu) mineralization at the Ilkwang deposit in the Gyeongsang Basin, South Korea is associated with the crystallization of a Cretaceous granitic rocks, hydrofracturing, and exsolution of magmatic hydrothermal fluids. An assemblage of quartz, chalcopyrite, pyrrhotite and tourmaline with a minor amount of arsenopyrite, garnet, pyrite, sphalerite and galena have precipitated from exsolving fluids and cemented the breccia fragments, showing clast-supported textures. Three distinct fluid inclusion assemblages in the vein quartz trapped aqueous fluids that transported and precipitated economic chalcopyrite. The earliest fluid can be represented by a CO2-bearing vapor-rich type IV inclusion assemblage (IVA). The CO2-bearing fluid (2–4 wt% NaCl equiv.) was trapped during the initial stages of brecciation and pressure decrease. Later brecciation events and continued decreasing pressure in the magma chamber generated low-salinity, supercritical fluids that boiled to produce brine (40–48 wt% NaCl equiv.) and coexisting vapor (2–13 wt% NaCl equiv.) at 343–493℃ and 120–400 bars. The textural evidence and microthermometric behaviors of the fluid inclusions suggest that Cu-mineralization at Ilkwang is a product of hypogene hydrothermal processes that were strongly pipe-controlled, highlighting the important role of fluid boiling in the formation of the Cu-mineralization. A combination of the fluid immiscibility of supercritical magmatic fluids and pressure changes created favorable environments, culminating in Cu mineralization during the boiling stage.

  SE16-D5-PM2-P-015 (SE16-A009)
 
K-Ar Dating of Clay Gouges from the Red River Fault Zone of Vietnam
Hoang Bac BUI1#+, Thanh NGO1, Yungoo SONG2, Itaya TETSUMARU3, The Hung KHUONG1, Tien Dung NGUYEN1
1 Hanoi University of Mining and Geology, Viet Nam, 2 Yonsei University, South Korea, 3 Okayama University of Science, Japan
#Corresponding author: buihoangbac@humg.edu.vn +Presenter

The Red River - Ailaoshan Fault Zone (RR-ASFZ), which is extended more than 1000 km from eastern Tibet to Tonkin Gulf, is a major tectonic feature separating South China from Indochina blocks since Eocene, accommodating the Indian–Eurasian plate collision and subsequent post-collisional evolution. Even various age data reported, however, the controversies over the timing and duration movement of the RR-ASFZ still remain. This study is the first attempt to identify authigenic illite formed in fault gouges of the RR-ASFZ at Lao Cai province, Vietnam and to directly constrain the movement of this fault by using K‐Ar dating of the newly formed illite. Two fault gouge samples were collected from the RR-ASFZ at Lao Cai province, Vietnam and were separated into three grain-size fractions (<0.1μm, 0.1-0.4 μm and 0.4-1.0μm).

The illite crystallinity index values for the different size fractions ranged from 1.02 to 0.52 which is representative of diagenetic metamorphic conditions at a temperature less than 180°C. The XRD patterns for the oriented-mounted samples indicated that illite has the dominant content in different size fractions. The results of illite-polytype quantifications using full-pattern-fitting with the WILDFIRE© simulated pattern show the percentages of detrital and authigenic illite and the R % values. The K-Ar ages decrease from coarse- to fine-grained fractions, suggesting enrichment infiner fraction of more-recently grown authigenic illites. The K-Ar ages of the fractions range from 24.1 to 19.2 Ma. The 1Md/1M illite ages determined by lower intercepts indicate the timing of 1Md/1M illite–precipitation at 19.2±0.92 Ma and 19.4±0.49 Ma. The age of this study together with the available chronological records suggests the preservation of evidence for the timing of sinistral ductile shearing of RR-ASFZ in Cenozoic. The results also indicated that the termination of ductile deformation along RR-ASFZ may have lasted to ca. 19 Ma. 

  SE16-D5-PM2-P-016 (SE16-A021)
 
The Characteristic of Lebong Tambang Vein Based on Quartz Textures and Au-Ag Grade : Possibility of Structural Controls and Wallrock Contacts
Eti SURYANI1+, Adi HANDARBENI2#
1 PT. Tansri Madjid Energy, Indonesia, 2 PT Sugico, Indonesia
#Corresponding author: adi.handarbeni@yahoo.com +Presenter

Lebong Tambang has long been known as having a potential gold in several locations where once a Dutch company in Dutch colonial era mined gold and silver from 1899 – 1941 (van Leeuwen 1994), is located at North Lebong District, Lebong Regency, approximately 250 km northeast of Bengkulu city. Hulusimpang Formation and Quarter Volcanoes with Telisa Formation as the oldest formation is the rocks unit in Lebong Tambang. Mineralization zone in the research area is part of Lebong Cluster precious metal prospects where the mineralization is related to the ‘Ketaun Structural Trend’. Tectonically, the zone is influenced by northeast-southwest trending Sumatra Great Fault in the east of the zone. Mineralization in Lebong Tambang area is associated with the bonanza veins that were formed in dilatant extensional settings, closely associated with dacite intrusions (Henley & Etheridge, 1995).

Lebong Tambang is a low-sulphidation epithermal deposit, gold and silver mineralization indicated by the occurrence of chalcedony-quartz veins pseudo-morphed calcite-rhodochrosite-adularia filling between chalcedonic bands. Detail mapping of five tunnel was observed, generally, the main veins are oriented in N 330° E (NNW-SSE) with 65° to 80° dips, thickness reaching 10 meters along 100 meters strike parallel to Lebong normal fault. Many minor vein and veinlet cut the main vein at normal, oblique, and almost parallel angles. Based on 49 rock chip samples taken from tunnel, can be classified into four vein textures : massive quartz vein (QCM), breccia quartz vein (QVBx), colloform-crustiform quartz vein (QVCC), and colloform-banding quartz vein (QVCo). The results of gold analysis from each vein texture show a various value but indicate the distributive trend of quartz vein-forming. High-gold content significantly exist in crustiform-colloform vein texture (>50 gr/t Au), otherwise lower-gold content exist in other vein textures. However, core samples analysis show the different results which is crustiform-colloform texture is not always indicate high-gold content, and there is also found gold content anomaly on quartz vein along hanging wall. It can be assumed that gold mineralization is not only correlated to its vein textures but also effected by structural controls, suggesting different stages along quartz-forming, and wallrocks contacts.

Keywords : Lebong Tambang, epithermal low-sulphidation, quartz textures

  SE17-D5-PM2-P-005 (SE17-A004)
 
Surface Rupture Geometry and Size of the Great 1950 Assam Earthquake
Aurelie COUDURIER-CURVEUR1#+, Elise KALI1, Paul TAPPONNIER1, Cagil KARAKAS2, Sorvigenaleon ILDEFONSO2, Jerome VAN DER WOERD3, Saurabh BARUAH4, Swapnamita VAIDESWARAN5, Emile OKAL6, Paramesh BANERJEE1
1 Nanyang Technological University, Singapore, 2 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 3 IPGS-School and Observatory of Earth Sciences, France, 4 North-East Institute of Science and Technology, India, 5 Wadia Institute of Himalayan Geology, India, 6 Northwestern University, United States
#Corresponding author: acoudurierc@ntu.edu.sg +Presenter

The East Himalayan Syntaxis, North East India, has been the site of one of the largest recorded continental earthquakes: the 1950 Assam earthquake, M=8.7. While its epicenter is located in China, close to a large strike slip fault, most of the damages, aftershocks, landslides, and debris flows occurred all around the Arunachal Pradesh plain surrounded by three major thrust fault systems. Characterization of the focal mechanism associated with that earthquake, and therefore identification of the fault plane(s) involved in the rupture, are still matter of controversy. Few studies have been carried out in that area to carefully report evidence of surface rupture, limiting our understanding of the earthquake mechanism, spatial extent and geometry of the event source. Using high-resolution satellite imagery analysis, morpho-tectonic field observations, and Total Station field surveys, we characterize the surface rupture geometry associated with the 1950 earthquake over a distance of at least 200 km along the Main Himalayan Frontal Thrust and the Mishmi Thrust. The data support the inference that both major thrusts ruptured during the 1950 event with different co-seismic offset values, and with evidence for characteristic slip on both thrusts. Ongoing dating of uplifted alluvial terraces will help us to constrain slip rates, occurrence, and return times of mega earthquakes at the East Himalayan Syntaxis.

  SE17-D5-PM2-P-006 (SE17-A005)
 
High Resolution Topography and Multiple Seismic Uplift on the Main Frontal Thrust Near the Ratu River, Eastern Nepal
Cagil KARAKAS1#+, Paul TAPPONNIER2, Soma Nath SAPKOTA3, Yann KLINGER4, Aurelie COUDURIER-CURVEUR2, Sorvigenaleon ILDEFONSO1, Mingxing GAO1, Laurent BOLLINGER5
1 Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 Nanyang Technological University, Singapore, 3 Department of Mines and Geology, Nepal, 4 Institute of Earth Physics of Paris, France, 5 DASE, France
#Corresponding author: ckarakas@ntu.edu.sg +Presenter

Traces of the M ≈ 8.4, 1934 Bihar-Nepal and 1255 AD earthquake ruptures are clear along the Himalayan Main Frontal Thrust from at least 85°49’ to 86°27’ E in eastern Nepal. We show new high-resolution, quantitative evidences of surface rupture, relative and co-seismic uplift in the Ratu river area. We present a map of uplifted terrace surfaces and abandoned paleo-channels truncated by the MFT, based on field observations, interpretation of stereoscopic air photos and high-resolution satellite images, topographic maps and newly acquired Digital Elevation Models from Total station and Terrestrial Lidar Scanner (TLS) surveys. We identify at least, five distinct uplifted terrace levels rising parallel to the riverbed on top of folded Siwaliks. Several sets of measurements may be taken to imply characteristic increments of throw during a sequence of at least five events of riverbed abandonment possibly related to co-seismic uplifts. High-resolution DEM extraction from new UAV surveys, kinematic GPS profiles and 14C ages of newly collected charcoal samples are still in progress and will help better constrain uplift and shortening rates over the length of the Bardibas thrust. Finally, we present a first order synthetic comparison of the heights and ages of potentially coeval co-seismic and cumulative scarps between our different sites of study.

  SE17-D5-PM2-P-007 (SE17-A006)
 
Characteristics of Strike-Slip Fault Deformation at Coastal Area - An Example of Yatsushiro Sea
Masatoshi YAGI#+
Tokai University, Japan
#Corresponding author: 3btad010@mail.tokai-u.jp +Presenter

The 100km long Futagawa-Hinagu fault zone is extending from the Aso volcano to the Yatsushiro-sea. Recent activity of Futagawa-Hinagu fault zone is mainly characterized by right lateral movement and the horizontal displacement (Chida, 1979)

Study target is the Yatsushiro-sea area at south western part of Futagawa-Hinagu fault zone. A number of sub aerial faults exist in the Yatsushiro-sea. The average rate of the activity interval and displace has not clearly until now.

We have carried out the high-resolution seismic surveys to comprehend the features of faults evolution process due to strike-slip fault. Results of survey, Main fault (MA fault) with NE-SW trending is observed. And we recognized some characteristic features around the MA fault. We divided into two sub-areas 1) North part of MA fault, and 2) South part of MA fault. We describe results for each sub-area as follow:

Sub-area 1

In-cross-sections, sub-vertical fault deformed the seafloor and sediments. This feature suggests the positive flower structure. And some ditched landforms with NW-SE trending are observed on the acoustic basement. These Landforms are distributes to parallel array. Displacement of faults becomes smaller to the south.

Sub-area 2

MA fault splayed off here. Almost these faults had normal components and forming a graben structure. Also, some faults separate acoustic basement to some blocks. These blocks are shows horseback-like landforms.

As described above, we have captured the features of the deformation structures, three-dimensionally. We plan to submarine topography survey and piston coring in the future.

  SE19-D5-PM2-P-015 (SE19-A002)
 
Present-Day Crustal Deformation of Linfen Basin and its Boundary Faults
Liu RUICHUN#+
Earthquake Adminstration of Shanxi Province, China
#Corresponding author: 24547716@qq.com +Presenter

Stacking-InSAR technology was used to measure the average crustal deformation rate of Linfen Basin and its boundary faults during 2003-2010.The results show that the inner part of Linfen Basin was subsiding and the mountains on both sides were rising relatively.The differential movement rate in middle section of Luoyunshan fault was 4mm/a,the rate in southern section was 6mm/a,and the rate around the fault was about 2mm/a, which corresponds with the result of the cross-fault leveling at the same time.Within Linfen basin,different tectonic units had different deformation patterns,the rate increased gradually from north to south.The rate in the northern part and in the southern part of Hongtong-Linfen Depression was 0-4mm/a and 4-8mm/a respectively.The Xiangfen Bulge was stable.The rate in the northeast part of Houma Depression was 4-8mm/a,and 8-12mm/a in the west part.

  SE19-D5-PM2-P-016 (SE19-A006)
 
Hybrid Ground Motion Simulation for the 2013 Ruisui, Taiwan Earthquake
Yi-Ying WEN1#+, Yin-Tung YEN2
1 National Chung Cheng University, Taiwan, 2 Sinotech Engineering Consultants, Inc, Taiwan
#Corresponding author: yiyingwen@ccu.edu.tw +Presenter

On 2013 October 31, the Mw 6.3 Rueisuei earthquake struck the northern part of the 150-km-long Longitudial Valley, a suture zone between the Philippine Sea plate and the Eurasian plate. The background seismicity shows that the epicenter is located in a seismic gap during the past two decades. According to the global CMT solution, the 2013 Rueisuei event shows a thrust-motion focal mechanism with the aftershock distributing along a west-dipping fault plane. Seismic data with different frequency band connote diverse scale of source character. The slip model derived by the previous study using long-period seismic data has provided us a preliminary property of earthquake source in low-frequency energy radiation. Furthermore, high frequency part of seismic energy needs to be concerned for the strong motions in comprehensive frequency band. We, thus, carried out simulation through the hybrid scheme that simulated waveforms combining the low-frequency motions (frequency-wavenumber integration method) and high-frequency motions (empirical Green’s function method) to reveal the strong ground motion and source character of the 2013 Rueisuei earthquake. The result shows that the 2013 Rueisuei earthquake displays clear rupture directivity to the northeast, which is consistent with the observed peak ground velocity distributions.

  SE19-D5-PM2-P-017 (SE19-A010)
 
Paleoseismic Study Across the Sagaing Fault Near Nay Pyi Taw, Central Myanmar
Saw Ngwe KHAING1#+, Soe Thura TUN2, Soe MIN3, Lin Thu AUNG2, Phyo Maung MAUNG4, Thura AUNG5
1 Hinthada University, Myanmar, 2 Myanmar Geosciences Society, Myanmar, 3 Taungoo University, Myanmar, 4 Department of Meteorology and Hydrology, Myanmar, 5 Myanmar Earthquake Committee, Myanmar
#Corresponding author: sawngwekhaing@gmail.com +Presenter

A paleoseismological excavation across the Sagaing Fault near Nay Pyi Taw unveils the evidences for two ruptures and 29-36 cm total offset. The dextral strike-slip fault is oriented N8°W in the study area and the east facing alluvial fault scarp is 0.4-0.6 m high. The trenches show stratigraphic and structural evidences for a minimum of two distinct ruptures in two trench locations. The stratigraphic evidences in the trench walls and the two ruptures are assumed to occur in the same event. Charcoals from the trenches are dated the most recent event to have occurred AD 1794-1829 (±30) (C14 ages). According to the historical earthquake records in Myanmar, this event is most likely prior to ~AD 1839.

Keywords: Palaeoseismic study, Sagaing Fault, Nay Pyi Taw, two ruptures, stratigraphic record, 1839 event

  SE19-D5-PM2-P-018 (SE19-A014)
 
Crustal Geometry of the Active Shanchiao Fault, Taipei Metropolis
Chih-Tung CHEN1#+, Jian-Cheng LEE1, Yu-Chang CHAN1, Chia-Yu LU2, Louis S. TENG2
1 Academia Sinica, Taiwan, 2 National Taiwan University, Taiwan
#Corresponding author: kthomasch@gmail.com +Presenter

The Shanchiao Fault is an active normal fault with documented paleoearthquakes in the Taipei Metropolis, Taiwan. While posing direct seismic threat on the multi-million population, its crustal-scale fault plane configuration has not been constrained and therefore attempted here by forward modeling late-Quaternary deformation. Tectonic subsidence over the last ~23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline. A 2-D profile across the Shanchiao Fault is chosen for elastic half-space dislocation modeling, and the results suggest that the fault is listric in the shallow crust with an abrupt change from sub-vertical ramp (~75°) to near-horizontal flat (~15°) at ~3 km depth, consistent with an origin from the inversion of an orogen-related thrust detachment. Given the presence of rift-related fabrics in the underthrust Chinese Continental Margin basement beneath the Taiwanese orogenic wedge, listric ramp-flat-ramp models with a second deeper bend to 60° dip are also tested. Reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth, which correlates with the hypocentral location of a moderate earthquake in 2004. Such geometry of the Shanchiao Fault bears key implications for seismic hazard in the Taipei area.

  SE19-D5-PM2-P-019 (SE19-A015)
 
Earthquake Geology of the Central Sagaing Fault, Myanmar
Yu WANG1#+, Paul TAPPONNIER1, Thura AUNG2, Chung-Han CHAN1, Lin Thu AUNG3, Kerry SIEH1
1 Nanyang Technological University, Singapore, 2 Myanmar Earthquake Committee, Myanmar, 3 Myanmar Geosciences Society, Myanmar
#Corresponding author: Y.Wang@ntu.edu.sg +Presenter

Using high-resolution optical satellite imagery (HRS) and digital elevation model (DEM), we mapped the detailed surface trace of the central Sagaing fault. This approximately 350-km-long section of the Sagaing fault, which slips at about 2 cm/yr, lies only ~ 10 km west of the densely populated city of Mandalay. Much of this stretch of the fault has not produced any major earthquakes in 20th century, and has been a seismic gap for more 150 years.

Our new geomorphic mapping from satellite-based data reveals complex deformation patterns along the northern part of the central Sagaing fault. The high-resolution DEM shows clear evidence of active dextral transpression along the fault, consistent with the minor shortening revealed by GPS. A series of small right-stepping step-overs characterize the fault north of the Irrawaddy River, forming a series of overlapping dextral scarps. South of the Irrawaddy River, the fault clearly offsets several channels on the young fluvial surface, indicating recent surface faulting at this section.

Our preliminary field and remote sensing observations suggest that the 1839 Ava earthquake, which may be the latest, largest destructive event at this section, was a great earthquake. We found minimum right-lateral displacements of about 5 to 7 meters along the 100-km-long mapped fault section. Such large amounts of plausibly single event offsets suggest that the moment magnitude of the last earthquake may have ranged between 7.4 and 8+. The corresponded fault surface rupture length could scale with up to 300+ km along the current seismic gap. The felt records of the Ava earthquake in 1839 further support our Mw 8 interpretation. The ground-motion scenarios of Mw 8.0 earthquake that ruptures the entire Sagaing fault seismic gap matches to the seismic intensity records in 1839. Further paleoseismological investigations will be carried out to confirm the recent activities of the fault.