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Anatexis in Himalayan crust:Evidence from geochemical and chronological investigations of Higher Himalayan Crystallines

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Science china Earth Sciences 2005年第9期48卷 1347-1356页

作者： YANG Xiaosong1. JIN Zhenmin2 & MA Jin1.1. State Key Laboratory of earthquake Dynamics, {1. of Geology, china earthquake administration, Beijing 1.0029, china 2. Faculty of Earth Sciences, china University of Geosciences, Wuhan 4.0074. china 1. State Key Laboratory of earthquake Dynamics Institute of Geology China Earthquake Administration 100029 Beijing China 2. Faculty of Earth Sciences China University of Geosciences 430074 Wuhan China

Migmatization in Higher Himalayan Crystallines (HHC) results from anatexis. The widely distributed migmatites in HHC are an important clue to investigate the relationship be- tween anatexis and the origins of Higher Himalayan leucogranites (HHL), and to understand the effect of anatexis on crustal evolution during the post-collision period. We studied in detail the chemical features of three basic constituent parts of the migmatites, i.e. leucosome, mesosome and melanosome, and determined the K-Ar ages of leucosomes. Our studies indicate that type-I leucosome is the product of crystallization of melt generated by partial melting of mesosome at source region, but type-II leucosome and HHL probably underwent crystallization differentiation of plagioclase during melt aggregation and migration. The age of 22.67 Ma of Type-I leucosome, which is a little older than the beginning of MCT movement, indicates that anatexis may have played an important role in the formation of MCT. That the ages of type-II leucosome (ranging from 1.0}82 to 1..37 Ma) are consistent with that of HHL provides new chronological evidence for the relationship between migmatization and HHL. We obtained a very young age of 6.23 Ma of Type-II leucosome that provides new time constraint on magma activity in the central segment of Higher Himalayas.

关键词： Higher Himalayan Crystallines, migmatite, anatexis, leucosome, K-Ar age.

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A preliminary study on seismic design criteria of offshore platforms in Bohai Sea of china

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earthquake Engineering and Engineering Vibration 2010年第2期9卷 223-231页

作者： Peng Yanju1.Lu Yuejun1.Yan Jiaquan2,Tang Rongyu1.Wang Junqin3 and Li Jiagang3 1. institute of Crustal Dynamics,{1. earthquake administration,Beijing 1.0085,{1. 2. institute of Geophysics,{1. earthquake administration,Beijing 1.0081.{1. 3. Beijing Research Center of {1. National Offshore Oil Corp.,Beijing 1.0027,{1. institute of Crustal Dynamics China Earthquake Administration Beijing 100085 China

This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 4. platforms located in the Bohai Sea,a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method,a scheme of two seismic design levels is proposed,and two seismic design objectives are established respectively for the strength level {1. and the ductility level {1.. By analogy with and comparison to the Chinese seismic design code for buildings,it is proposed that the probability level for the strength level {1. and ductility level {1. have a return period of 200 and 1.00 - 2500 years,respectively. The validity of these proposed values is discussed. Finally,the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea.

关键词： fixed offshore platform seismic design level seismic design objective return period Bohai Sea

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Source mechanism of strong aftershocks (M_s≥5.6) of the 2008/05/1. Wenchuan earthquake and the implication for seismotectonics

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Science china Earth Sciences 2009年第6期52卷 739-753页

作者： ZHENG Yong1.2,MA HongSheng3,Lü Jian4.NI SiDao5,LI YingChun6 & WEI ShengJi2 1.{1. of Geodesy and Geophysics,Chinese Academy of Sciences,Wuhan 4.0077,china 2.institute of Geophysics,Chinese earthquake {4.,Beijing 1.0086,china 3 {1. of earthquake Science,Chinese earthquake {4.,Beijing 1.0086,china 4.earthquake {4. of Jiangxi Province,Nanchang 330039,china 5 School of Earth and Space Science,University of Science and Technology of china,Hefei 230026,china 6 earthquake {4. of Jiangsu Province,Nanjing 21.01.0}china 1. institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China 2. institute of Geophysics Chinese Earthquake Administration Beijing 100086 China 3. institute of {1. Science Chinese Earthquake Administration Beijing 100086 China 4. {1. administration of Jiangxi Province Nanchang 330039 China 5. School of Earth and Space Science University of Science and Technology of China Hefei 230026 China 6. earthquake {1. of Jiangsu Province Nanjing 210014 China

Dozens of >M5, hundreds of >M4. and much more >M3 aftershocks occurred after the 2008/05/1. Wenchuan {1., which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the >M3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of china, and employed 'Cut and Paste' method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6). While most of those aftershocks show thrust mechanism, there are some strike slip {1.s in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust {1.s, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (~1. km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.

关键词： focal mechanism seismotectonics Wenchuan earthquake cut and paste.

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Deep tectonic setting of the 2008 Wenchuan M_s8.0 earthquake in southwestern {1.―Joint analysis of teleseismic P-wave receiver functions and Bouguer gravity anomalies

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Science china Earth Sciences 2009年第2期52卷 166-179页

作者： LOU Hai1. WANG ChunYong1. L ZhiYong2, YAO ZhiXiang1. DAI ShiGui2 & YOU HuiChuan1.1.institute of Geophysics,{1., Beijing 1.0081. china 2 earthquake {4. of Sichuan Province, Chengdu 61.04., china 1. institute of Geophysics China Earthquake Administration Beijing 100081 China 2. earthquake {1. of Sichuan Province Chengdu 610041 China

Teleseismic P-wave receiver functions at 20 broadband seismic stations in the Longmenshan fault zone (LMFZ) and its vicinity were extracted, and the crustal thickness and the P- and S-wave velocity ratio were calculated by use of the H-k stacking algorithm. With the results as constraints, the S-wave ve-locity structures beneath each station were determined by the inversion of receiver functions. The crustal structure of the Rear-range zone is similar to that of the Songpan-Garze Block, whereas the velocity structure of the Fore-range zone resembles that of Sichuan Basin, implying that the Central Principal Fault of LMFZ is the boundary between the eastern Tibetan Plateau and the Yangtze Block. Lower velocity zone exists in lower crust of the Songpan-Garze Block and the central-southern seg-ment of the Rear-range zone, which facilitates the detachment of the material in upper and middle crust. Joint analysis of the receiver functions and the Bouguer gravity anomalies supports the thesis on the detachment-thrust mode of the LMFZ. A double-detachment pattern is suggested to the tectonic setting in the Songpan-Garze Block. The upper detachment occurs at the depth of 1.-1. km, and represents a high-temperature ductile shear zone. There is a lower detachment at the depth of about 30 km, below which the lower crust flow exists in the eastern Tibetan Plateau. Interpretation of the Bouguer gravity anomalies indicates that the Sichuan Basin is of higher density in upper and middle crust in compari-son with that of the Songpan-Garze Block. The LMFZ with higher density is the result from the thrusting of the Songpan-Garze Block over the Sichuan Basin. In the lower crust, higher P velocity and higher density in the Sichuan Basin are related to more rigid material, while lower S velocity and lower density in the Songpan-Garze Block are related to the softened and weakened material. The higher density block beneath the Sichuan Basin obstructs the eastward flow of lower crustal ma

关键词： Longmenshan fault zone (LMFZ) Wenchuan Ms8.0 earthquake deep tectonic setting teleseismic receiver function

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Geophysical survey on the tectonic and sediment distribution of Qinghai Lake basin

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Science china Earth Sciences 2006年第8期49卷 851-861页

作者： AN Zhisheng1, WANG Ping2, SHEN Ji3, ZHANG Yixiang2, ZHANG Peizhen4. WANG Sumin3, LI Xiaoqiang1, SUN Qianli1, SONG Yougui1, AI Li1, ZHANG Yechun2, JIANG Shaoren2, LIU Xingqi3 & WANG Yong31. institute of Earth Environment, Chinese Academy of Sciences (CAS), Xi’an 710075, china 2. South china Sea institute of Oceanology, CAS, Guangzhou 510301, china 3. Nanjing institute of Geography and Limnology, CAS, Nanjing 210008, china 4. institute of Geology, china earthquake administration, Beijing 100029, china 1. institute of Earth Environment Chinese Academy of Sciences (CAS) Xi’an 710075 China 2. South china Sea {1. of Oceanology CAS Guangzhou 510301 China 3. Nanjing institute of Geography and Limnology CAS Nanjing 210008 China 4. {1. of Geology China Earthquake Administration Beijing 100029 China

The intensive geophysical survey of Qinghai Lake reveals the buried depth of lake sediments and their distribution features. The result indicates that there are three important inter- phases of Qinghai Lake sediments: T1.is the rife interphase of the lake, above which sediments are spread all over the lake basin with roughly the same thickness; T5 is the interphase from which the neotectonic sedimentary cycle begins, and its above sedimentary environment is relatively stable; Tg is the base of the lake basin. Five west-northwest (WNW) fault belts defined the tectonic structure of Qinghai Lake basin: the central hunch around Haixin Shan with two subbasins both in its north and south. The thickness of the lake sediments varies at different places, the thickest sediments are found within the two subbasins. According to the depth that the Sparker System can reach, sediment in the northern subbasin is deeper than 560 m, while sediment in the southern subbasin is deeper than 700 m. The correlation between the seismic sequence stratigraph and the lithology of onshore core shows that Qinghai Lake sediments consist of muddy silt, clay silt, silty clay, gravel silty clay, etc.

关键词： sediment, geophysical survey, Qinghai Lake.

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The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

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Science china Earth Sciences 2008年第8期51卷 1064-1080页

作者： YANG ShaoMin1.2, LI Jie1.3 & WANG Qi2,1.1.Research Center of Space Science and Technology, china University of Geosciences, Wuhan {1.007{1. china 2.institute of Seismology, china earthquake administration, Wuhan {{1. china 3 earthquake administration of Xinjiang Uygur Autonomous Region, Urumqi 83001., china 1. Research Center of Space Science and Technology China University of Geosciences Wuhan 430074 China 2. institute of Seismology China Earthquake Administration Wuhan 430071 China 3. earthquake {1. of Xinjiang Uygur Autonomous Region Urumqi 830011 China

Based on GPS measurements conducted from 1.92 to 2006, we present the current crustal movement velocity field for approximately 4.0 sites in the Tianshan Mountains and their adjacent areas, and estimate slip rates on the major faults using a 2-D elastic dislocation model. Our studies show slip rates within the range of 1.4.mm/a on the NW-SE trending strike-slip faults (such as Talas-Fergana fault) in the Tianshan Mountains. We also found the slip rates on the approximately WE-SN trending gently-dipping detachment fault vary from 1.―1. mm/a for the southwest Tianshan Mountains to 2―5 mm/a for the eastern Tianshan Mountains, and to 6―1. mm/a for the Kyrgrz Tianshan. The GPS velocity field reveals that the total convergence is not uniformly distributed across the Tianshan Mountains, with 80%―90% of the N-S shortening absorbed along the southern and northern edges, and relatively little deformation accommodated within the interior. This first-order feature of strain pattern is explained best by underthrusting of adjacent blocks beneath the Tianshan Mountains along a basal detachment fault. We found the occurrence of historical M7―8 earthquakes somewhere in the locked ramp that connects the creeping and locking segments of the detachment, thereby resulting in elastic strain concentration and accumulation around it. The elastic strain confined in the upper crustal layer above the detachment ultimately releases through infrequent great earthquakes in the Tianshan Mountains, resulting in considerable folding and faulting at their margins. The Tianshan Mountains propagated outward and rose progressively as a wedge-shaped block.

关键词： Tianshan Mountains GPS slip rates tectonic deformation

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Dynamic mechanisms of the post-seismic deformation following large events:Case study of the 1.99 Chi-Chi earthquake in Taiwan of {1.

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Science china Earth Sciences 2009年第11期52卷 1813-1824页

作者： ZHU ShouBiao1.2 & CAI YongEn2 1.institute of Crustal Dynamics,{1., Beijing 1.0085, china 2 Department of Geophysics, Peking University, Beijing 1.0871. china 1. institute of Crustal Dynamics China Earthquake Administration Beijing 100085 China 2. Department of Geophysics Peking University Beijing 100871 China

The mechanism of postseismic deformation related to strong earthquakes is important in geodynamics, and presumably afterslip or viscoelastic relaxation is responsible for the postsesimic deformation. The 1.99 Chi-Chi, Taiwan of {1., earthquake occurred in the region where GPS observation station is most densely deployed in the world. The unprecedented GPS data provides a unique opportunity to study the physical processes of postseismic deformation. Here we assume that the interactions of viscoelastic relaxation, afterslip, fault zone collapse, poroelastic rebound, flow of underground fluids, and all these combined contribute to the surface displacements following the main shock. In order to know the essence of the postseismic deformation after the strong event, fault zone collapse, poroelastic rebound, flow of underground fluids, and so on, are represented equivalently by the variations of the focal medium properties. Therefore, the viscoelastic relaxation, afterslip, and the variations of the equivalent focal medium properties are inverted by applying the GPS temporal series measurement data with viscoelastic finite element method. Both the afterslip rate distribution along the fault and the afterslip evolution with time are obtained by means of inversion. Also, the preliminary result suggests that viscosities of the lower crust and the upper mantle in Taiwan region is 2.7×1.1. and 4.2×1.20 Pa·s, respectively. Moreover, the inversion results indicate that the afterslip contributing to postseismic deformation of 4..6% in 4.0 days after the Chi-Chi earthquake, with 34.7% caused by the viscous relaxation and 20.7% by other factors such as fault zone collapse, poroelastic rebound, and the flow of liquids.

关键词： mechanism of postseismic deformation viscoelastic finite element method GPS temporal series data Chi-Chi earthquake

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Velocity structure and active fault of Yanyuan-Mabian seismic zone―The result of high-resolution seismic refraction experiment

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Science china Earth Sciences 2008年第9期51卷 1284-1296页

作者： WANG FuYun1., DUAN YongHong1. YANG ZhuoXin1. ZHANG ChengKe1. ZHAO JinRen1. ZHANG JianShi1. ZHANG XianKang1. LIU QiYuan2, ZHU AiLan2, XU XiWei2 & LIU BaoFeng1.1.Geophysical Exploration Center, china earthquake administration, Zhengzhou {1.0002, china 2.institute of Geology, china earthquake administration, Beijing 1.0029, china 1. Geophysical Exploration Center China Earthquake Administration Zhengzhou 450002 China 2. institute of Geology China Earthquake Administration Beijing 100029 China

The authors processed the seismic refraction Pg-wave travel time data with finite difference tomography method and revealed velocity structure of the upper crust on active block boundaries and deep features of the active faults in western Sichuan Province. The following are the results of our investigation. The upper crust of Yanyuan basin and the Houlong Mountains consists of the superficial low-velocity layer and the deep uniform high-velocity layer, and between the two layers, there is a distinct, and gently west-dipping structural plane. Between model coordinates 1.0-24. km, P-wave velocity distribution features steeply inclined strip-like structure with strongly non-uniform high and low velocities alternately. Xichang Mesozoic basin between 24. and 300 km consists of a thick low-velocity upper layer and a high-velocity lower layer, where lateral and vertical velocity variations are very strong and the interface between the two layers fluctuates a lot. The Daliang Mountains to the east of the 300 km coordinate is a non-uniform high-velocity zone, with a superficial velocity of approximately 5 km/s. From 1.0 to 1.0 km and from 280 to 31. km, there are extremely distinct deep anomalous high-velocity bodies, which are supposed to be related with Permian magmatic activity. The Yanyuan nappe structure is composed of the superficial low-velocity nappe, the gently west-dipping detachment surface and the deep high-velocity basement, with Jinhe-Qinghe fault zone as the nappe front. Mopanshan fault is a west-dipping low-velocity zone, which extends to the top surface of the basement. Anninghe fault and Zemuhe fault are east-dipping, tabular-like, and low-velocity zones, which extend deep into the base-ment. At a great depth, Daliangshan fault separates into two segments, which are represented by drastic variation of velocity structures in a narrow strip: the west segment dips westward and the east segment dips eastward, both stretching into the basement. The east margin f

关键词： western Sichuan high-resolution seismic refraction active fault velocity structure of the upper crust

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The April 1.0}h, 201. Yushu {1., a devastating {1. with foreshocks

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Science china Earth Sciences 2010年第6期53卷 791-793页

作者： NI SiDao1. WANG WeiTao2 & LI Li3 1.School of Earth and Space Sciences, University of Science and Technology of china, Hefei 230026, china 2.institute of Geophysics, china earthquake administration, Beijing 1.0081. china 3 National earthquake Infrastructure Service, china earthquake administration, Beijing 1.0036, china 1. School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China2. Institute of Geophysics China Earthquake Administration Beijing 100081 China3. National Earthquake Infrastructure Service China Earthquake Administration Beijing 100036 China

In the early morning of April 1.0}h, 201., a strong earth- quake (Ms7.1. http://***; Mw6.9, http://neic. ***) occurred in Yushu district, Qinghai Province, {1.. More than 2000 lives were lost and over 1.0000 injured,

关键词： Figure Yushu earthquake a devastating earthquake with foreshocks The April 1.0}h 201. very than

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Discussion on moment tensor solution and seismogenic structure of Ruichang-Yangxin earthquake on 1. September 201.

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earthquake Science 2012年第3期25卷 229-234页

作者： Lifen Zhang1.2, Guichun Wei and Wulin Liao1.1.Key Laboratory of earthquake Geodesy, {1. of Seismology, china earthquake administration, Wuhan 4.0071. {4. 2.institute of Geophysics, china earthquake administration, Beijing 1.0081. {4. 1. Key Laboratory of earthquake Geodesy Institute of Seismology China Earthquake Administration Wuhan 430071 China 2. institute of Geophysics China Earthquake Administration Beijing 100081 China

Ruichang-Yangxin earthquake is another moderate earthquake in Yangxin-Jiujiang area since 2005 Jiujiang-Ruichang M5.7 earthquake. In order to more understand the seismic activities in this area, we study the moment tensor solution and the seismogenic structure of the Ruichang-Yangxin earthquake. Precise earthquake relocation shows that the mainshock occurred on the southwestern part of the NE-trending fault and aftershocks are distributed not only along the NE-trending fault but also along its conjugated NW-trending fault. By comprehensive analysis on the earthquake distribution, characteristics of isoseismal curve, focal mechanism, and regional structure characteristics, it is inferred that this earthquake is caused by the NE-trending Tanlu fault. In addition, it has close relationship with the conjugated NW-trending fault as well. Many researches have shown that the junction area is the earthquake-prone area, and should be paid more attention to. And our study also proves this viewpoint.

关键词： moment tensor inversion Ruichang-Yangxin earthquake seismogenic structure

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