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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 430074, China 2.institute of seismology, China{2. administration, wuhan 430071, China 3{2. administration of Xinjiang Uygur Autonomous Region, Urumqi 830011, 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 administration of Xinjiang Uygur Autonomous Region Urumqi 830011 China

Based on GPS measurements conducted from 1992.to 2.06, we present the current crustal movement velocity field for approximately 400 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 10―13 mm/a for the southwest Tianshan Mountains to 2.5 mm/a for the eastern Tianshan Mountains, and to 6―12.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

Deformation in the Three Gorges Reservoir after the first impoundment determined by GPS measurements

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Progress in Natural Science:Materials International 2005年第6期15卷 515-522页

作者： DU Ruilin 1,2., QIAO Xuejun 1,2.*, WANG Qi 1,2., XING Canfei 1,2.and YOU Xinzhao 1,3 (1. institute of seismology, CEA,{2., China 2. Laboratory of Crustal Movement and Earth Observation,{2., China 3. Center for Analysis and Prediction, CEA, Beijing 100036, China) institute of seismology CEA Wuhan 430071 China Laboratory of Crustal Movement and Earth Observation Wuhan 430071 China Center for Analysis and Prediction CEA Beijing 100036 China

A 6-year long GPS observation (1998—2.03) indicates that crustal deformation in the Three Gorges area is less active at a marginally measurable rate of 0—5 mm/a relative to stable South China block. However, the impounding water in June 2.03 has induced transient displacement at the Three Gorges dam and the emerging reservoir. GPS measurements after the first stage of water filling of the reservoir demonstrate that vertical subsidence close by Yangtze River is about 10—40 mm, and the horizontal displacement is less than 5—10 mm. The maximum subsidence induced by the impoundment is located in the segment of the reservoir from Maoping to Xiangxi. The water loading-induced deformation diminishes rapidly with the distance from banks of the reservoir. The overall pattern of transient deformation is consistent with the simulation result of Farrell, and is attributed to the elastic response of upper lithosphere crust to overlying water reservoir.

关键词： Three Gorges GPS impoundment deformation.

A circum-earth shear zone at low-latitudes and episodic large earthquakes in it and the circum-Pacific seismic zone

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Science China Earth Sciences 2006年第9期49卷 897-903页

作者： MA Zongjin1, DU Pinren1, REN Jinwei2.& GAO Xianglin1 1. institute of Geology, China earthquake{2., Beijing 10002., China 2. institute of earthquake Science, China earthquake{2., Beijing 100036, China 1. institute of Geology China Earthquake Administration Beijing 100029 China 2. institute of earthquake Science China Earthquake Administration Beijing 100036 China

Because of the differential motions between the Northern and Southern Hemispheres of the Earth, there exists a motion discordant zone between them. On the surface this zone consists of 13 large faults dominant with strike-slip. We call it a global shear zone at low-latitudes (E system). By statistical analysis of temporal distribution of earthquakes Mw≥7.5 in the E system and the circum-Pacific (P system) during 1900―2.03, we find that there exist quasi-episodic and alternative activities in and between these two systems. This phenomenon is likely associated with the half-sphere oscillation in dilation and contraction and the change of the Earth’s rotation rate.

关键词： shear zone, circum-Pacific zone, great earthquake, quasi-episode.

Discussion on moment tensor solution and seismogenic structure of Ruichang-Yangxin earthquake on 10 September 2.11

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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, institute of{2., China earthquake administration, wuhan 430071, China 2.institute of Geophysics, China earthquake administration, Beijing 100081, China 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 2.05 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

Average slip rate, earthquake rupturing segmentation and recurrence behavior on the Litang fault zone, western Sichuan Province, China

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Science China Earth Sciences 2005年第8期48卷 1183-1196页

作者： XU Xiwei1, WEN Xueze2. YU Guihua1, ZHENG Rongzhang1, LUO Haiyuan2.& ZHENG Bin2.1. institute of Geology, China earthquake{2., Beijing 10002., China 2. earthquake{2. of Sichuan Province, Chengdu 610041, China 1. institute of Geology China Earthquake Administration 100029 Beijing China 2. earthquake administration of Sichuan Province 610041 Chengdu China

The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Field investigation reveals new evidence for its late Quaternary offset, neoteric earthquake ruptures and surface-rupturing segmentation, from which long-term slip-rates, char-acteristic earthquake magnitudes and recurrence intervals on the fault zone are estimated. This study shows that the LFZ consists of three subordinate faults, and they are the northern Maoyaba fault, Litang fault and Kangga-Dewu fault, respectively. All of them are dominated by left-lateral strike-slip with reverse dip-slip component on different segments. Based on offset landforms and ages of relevant deposits collected from seven sites, it is estimated that the average left-lateral slip-rate on the LFZ reaches 4.0±1.0 mm/a in the past 14 ka BP, and vertical (reverse) dip-slip rate in the range of 0.1―1.8 mm/a. Three subordinate faults are independent earthquake rup-turing segments, on which the maximum moment magnitude of the characteristic earthquakes is estimated to be 7.0―7.3, and their average recurrence interval to be 500―1000 a. The latest earthquake ruptures occurred 119±2.years ago on the northern Maoyaba fault, about 1890 AD on the Litang fault, and in 1948 AD on the Kangga-Dewu fault, and this may indicate a unidirectional migration for surface rupturing earthquakes along the Litang fault zone, related to stress trigger-ing between the segments.

关键词： Litang fault zone, slip rate, earthquake rupturing segmentation, recurrence interval.

Distribution and characteristics of gravelly soil liquefaction in the Wenchuan M_s 8.0 earthquake

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earthquake Engineering and Engineering Vibration 2010年第2期9卷 167-175页

作者： Cao Zhenzhong1,Hou Longqing2.Xu Hongmei2.and Yuan Xiaoming1 1. institute of Engineering Mechanics,China earthquake{2.,Harbin 150080,China 2. East China institute of Technology,Fuzhou 344000,China institute of Engineering Mechanics China Earthquake Administration Harbin 150080 China

In this paper,a distribution map of gravelly soil liquefaction that was caused by the Wenchuan M8.0 earthquake in China is proposed based on a detailed field investigation and an analysis of geological soil profiles. The geological background of the earthquake disaster region is summarized by compiling geological cross sections and borehole logs. Meanwhile,four typical liquefied sites were selected to conduct sample drillings,dynamic penetration tests (DPT),and shear wave velocity tests,to understand the features of liquefied gravelly soil. One hundred and eighteen (118) liquefied sites were investigated shortly after the earthquake. The field investigation showed:(1) sandboils and waterspouts occurred extensively,involving thousands of miles of farmland,12. villages,eight schools and five factories,which caused damage to some rural houses,schools,manufacturing facilities and wells,etc.; (2. the Chengdu plain is covered by a gravelly soil layer with a thickness of 0 m to 541 m according to the geological cross sections; (3) there were 80 gravelly soil liquefied sites in the Chengdu plain,shaped as five belt areas that varied from 2. km to 40 km in length,and about ten gravelly soil liquefied sites distributed within Mianyang area; and (4) the grain sizes of the sampled soil were relative larger than the ejected soil on the ground,thus the type of liquefied soil cannot be determined by the ejected soil. The gravelly soil liquefied sites are helpful in enriching the global database of gravelly soil liquefaction and developing a corresponding evaluation method in further research efforts.

关键词： gravelly soil liquefaction borehole soil profile geological cross section grain size distribution Wenchuan earthquake

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, institute of Geology, China earthquake administration, Beijing 10002., China 2. Faculty of Earth Sciences, China University of Geosciences, wuhan 430074, 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 2..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 14.82.to 18.37 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 6.2. 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.

Evolution of terraces Ⅰ–Ⅲ along the Anning River, western Sichuan, based on pollen records and terrace structure

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Science China Earth Sciences 2011年第1期54卷 127-135页

作者： CHENG JianWu1,2.1 institute of Geology, China earthquake{2., Beijing 100039, China 2.earthquake{2. of Gansu Province, Lanzhou 730000, China institute of Geology China Earthquake Administration Beijing China earthquake administration of Gansu Province Lanzhou China

This study reconstructs the long-term evolution of river terraces over large spatial scales along the Anning River, western Sichuan, and identifies external factors controlling terrace formation. Pollen record analysis and terrace structure indicate that formation of the middle section of terraces I-III resulted from the interaction of changing climates and uplift of the margins of the Qinghai-Tibet Plateau. The relative influence of climate and uplift in terrace formation changes in different periods. The terraces reveal multiple, gradual uplift events on the eastern Qinghai-Tibet Plateau, which is of great significance for determining uplift mechanisms across the entire plateau.

关键词： Anning River in western Sichuan terrace formation pollen paleoclimate

Plumb line variation at Tangshan during 1987―1998 and its relation with the earthquakes around

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Science China Earth Sciences 2009年第1期52卷 101-107页

作者： LI ZhengXin1,2.& LI Hui3 1 Shanghai Observatory,Chinese Academy of Sciences,Shanghai 2.0030,China 2.institute of Geodesy and Geophysics,Chinese Academy of Sciences,Wuchang 430077,China 3 institute of{2.,China earthquake administration,Wuchang 430071,China Shanghai Observatory Chinese Academy of Sciences Shanghai 200030 China institute of Geodesy and Geophysics Chinese Academy of Sciences Wuchang 430077 China institute of seismology China Earthquake Administration Wuchang 430071 Chin

Plumb line variations(PLV) at Tangshan during the years of 1987―1998 are determined by using the 46 batch repeated gravity observations of the Beijing-Tangshan *** has been found that PLV at Tangshan are related with the 38 earthquakes in this *** appears that the time of an earthquake around Tangshan is usually quite the same when PLV at Tangshan begins moving in opposite direction.

关键词： plumb line variations network in northern China variations of local gravity field earthquakes