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Spatio-temporal variation of the stress field in the wenchuan aftershock region

Earthquake Science 2012年第5期25卷 517-526页

作者： Feng Long Guixi Yi xueze wen Zhiwei Zhang Earthquake Administration of Sichuan Province College of Geophysics Chengdu University of Technology Institute of Earthquake Science China Earthquake Administration

Focal mechanism solutions and centroid depths of 312 M≥4 aftershocks from the 2008 wenchuan earthquake sequence have been derived by CAP （Cut and Paste） method from broadband waveform data with relatively high signal-to-noise ratio （SNR）. Following this, we have analyzed the distribution of focal depths and the stress tensors, as well as the types of focal mechanisms. The major results are：（1） different cross-sections show that the depth ranges of the aftershocks at the southern and northern ends of the aftershock area along the Longmenshan fault zone are wider than those on the central segment, where rare M≥4 aftershocks occurred at depths shallower than 10 kin. The main faults trend to the NW on the southern and central segments, and for the northern segment, no dominant trend direction has been determined; （2） stress tensor distribution demonstrates that the majority of the aftershock areas on the cross-section along the major axis are mainly under compressive stress perpendicular to the profile; however, for the areas near Lixian, Beichuan, Qingchuan and the shallow parts of its northern segment, large principal stress components are parallel to the major axis profile direction. On the cross-sections perpendicular to the major axis, the three areas above can be divided into two parts： one with dominantly compressional stress near the major faults of the Longmenshan fault zone on the SE side, and the other with NE-direction push along the fault zone on the NW side; （3） the stress tensor distribution in map view is very similar to those on the vertical cross-sections. In map view, the orientation of the principal compressional stress axis $1 on the central segment of the aftershock area presents an SE-trending arc shape; （4） the stress tensor slices at different depths show that the orientation of S1 axis mainly changes on the central segment and at the northern end, indicating that the two segments have different seismogenic structures at different depths; （5） with the exception of the northern end of the aft

关键词： wenchuan earthquake sequence focal depth focal mechanism solution stress tensor stress field

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A seismic gap on the Anninghe fault in western Sichuan, China

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Science China Earth Sciences 2008年第10期51卷 1375-1387页

作者： xueze wen Jun Fan GuiXi Yi YiWei Deng Feng Long Institute of Earthquake Science China Earthquake Administration Beijing 100036 China College of Information Engineering Chengdu University of Technology Chengdu 610059 China Present address: Earthquake Administration of Sichuan Provinc

Through integrated analyses of time-varying patterns of regional seismicity, occurrence background of strong and large historical earthquakes along active faults, and temporal-spatial distribution of accu- rately relocated hypocenters of modern small earthquakes, this paper analyzes and discusses the im- plication of a 30-year-lasting seismic quiescence in the region along and surrounding the Anninghe and Zemuhe faults in western Sichuan, China. It suggests that the seismic quiescence for ML≥4.0 events has been lasting in the studied region since January, 1977, along with the formation and evaluation of a seismic gap of the second kind, the Anninghe seismic gap. The Anninghe seismic gap has the background of a seismic gap of the first kind along the Anninghe fault, and has resulted from evident fault-locking and strain-accumulating along the fault during the last 30 years. Now, two fault sections either without or with less small earthquakes exist along the Anninghe fault within the An- ninghe seismic gap. They indicate two linked and locked fault-sections, the northern Mianning section and the Mianning-Xichang section with lengths of 65 km and 75 km and elapsed time from the latest large earthquakes of 527 and 471 years, respectively. Along the Anninghe fault, characteristics of both the background of the first kind seismic gap and the seismicity patterns of the second seismic gap, as well as the hypocenter depth distribution of modern small earthquakes are comparable, respectively, to those appearing before the M=8.1 Hoh Xil earthquake of 2001 and to those emerging in the 20 years before the M=7.1 Loma Prieta, California, earthquake of 1989, suggesting that the Anninghe seismic gap is tending to become mature, and hence its mid- to long-term potential of large earthquakes should be noticeable. The probable maximum magnitudes of the potential earthquakes are estimated to be as large as 7.4 for both the two locked sections of the Anninghe fault.

关键词： Anninghe fault seismic quiescence seismic gap fault locking seismic potential

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Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan,China,that caused the 2008 wenchuan earthquake

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Earthquake Science 2011年第3期24卷 249-265页

作者： Tetsuhiro Togo Toshihiko Shimamoto Shengli Ma xueze wen Honglin He Department of Earth and Planetary Systems Science Graduate School of Science Hiroshima University Higashi-Hiroshima 739-8526 Japan State Key Laboratory of Earthquake Dynamics Institute of Geology China Earthquake Administration Beijing 100029 China Earthquake Administration of Sichuan Province Chengdu 610041 China

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 wenchuan earthquake, at an outcrop in Hongkou, Sichuan province, China. Present work is a part of comprehensive project of Institute of Geology, China Earthquake Administration, trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce wenchuan earthquake by modeling based on measured mechanical and transport properties. Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling, during the wenchuan Earthquake Fault Scientific Drilling （WFSD） Project, to understand along-fault and depth variation of fault zone properties. The hanging wall side of the fault zone consists of weakly-foliated, clayey fault gouge of about 1 m in width and of several fault breccia zones of 30-40 m in total width. We could not find any pseudotachylite at this outcrop. Displacement during the wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width. This is an important constraint for analyzing thermal pressurization, an important dynamic weakening mechanism of faults. Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters, so that localization of deformation must have occurred within a slipping zone during coseismic fault motion. Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon. Fault gouge contains illite and chlorite minerals, but not smectite. Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite. The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been drilled very close to the Hongkou outcrop. The presen

关键词： wenchuan earthquake Longmenshan fault system Beichuan fault fault rock fault mechanics fault-zone structure amorphous carbon graphite

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A fast automatic identification method for seismic belts based on distance correlation and its earthquake case

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Earthquake Science 2020年第3期33卷 153-158页

作者： Wei Yan xueze wen Changrong He Guiping Liu Zirui Li Institute of Geology China Earthquake AdministrationBeijing 100029China China Earthquake Networks Center Beijing 100045China Beijing Earthquake Agency Beijing 100080China Earthquake Agency of Ningxia Hui Autonomous Region Yinchuan 750001China

Earthquake prediction practice and a large number of earthquake cases show that anomalous images of small earthquake belts may appear near the epicenter before strong earthquakes.Through the research of earthquake cases,researchers have a relatively consistent method to determine the clarity of an identified seismic belt,but there is still a lack of method on seismic belt identification from the distribution of scattered points.Due to the complexity of exhaustive algorithm,the rapid automatic identification technique of seismic belts has been progressing slowly.Visual recognition is still the basic method of seismic belt identification.Based on the algorithm of distance correlation,this paper presents a fast automatic identification method of seismic belts.The effectiveness of this method was proved by 100 random earthquakes and an example of seismic belts of magnitude 4.0 before the 2005 Jiujiang M5.7 earthquake.The results show that:①the automatic identification of seismic belts should first identify the"relational earthquake",then identify the"suspected seismic belt",and finally use the criterion of seismic belt clarity to determine;②random earthquakes and real earthquakes identification results show that the distance correlation method can realize the fast automatic identification of seismic belts by computer.

关键词： seismic belt automatic identification relational earthquake suspected seismic belt belt clarity

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Discovery of the Longriba Fault Zone in Eastern Bayan Har Block, China and its tectonic implication

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Science China Earth Sciences 2008年第9期51卷 1209-1223页

作者： XU XiWei wen xueze CHEN GuiHua YU GuiHua Institute of Geology China Earthquake AdministrationBeijing 100029China Earthquake Administration of Sichuan Province Chengdu 610041China

Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet Plateau. The strain rate along this shear zone may reach up to 4-6 mm/a. Our interpretation of satellite images and field observations indicate that this dextral shear zone corresponds to a newly generated NE trending Longriba fault zone that has been ignored before. The northeast segment of the Longriba fault zone consists of two subparallel N54°±5°E trending branch faults about 30 km apart, and late Quaternary offset landforms are well developed along the strands of these two branch faults. The northern branch fault, the Longriqu fault, has relatively large reverse component, while the southern branch fault, the Maoergai fault, is a pure right-lateral strike slip fault. According to vector synthesizing principle, the average right-lateral strike slip rate along the Longriba fault zone in the late Quaternary is calculated to be 5.4±2.0 mm/a, the vertical slip rate to be 0.7 mm/a, and the rate of crustal shortening to be 0.55 mm/a. The discovery of the Longriba fault zone may provide a new insight into the tectonics and dynamics of the eastern margin of the Qinghai-Tibet Plateau. Taken the Longriba fault zone as a boundary, the Bayan Har block is divided into two sub-blocks: the Ahba sub-block in the west and the Longmenshan sub-block in the east. The shortening and uplifting of the Longmenshan sub-block as a whole reflects that both the Longmenshan thrust and Longriba fault zone are subordinated to a back propagated nappe tectonic system that was formed during the southeastward motion of the Bayan Har block owing to intense resistance of the South China block. This nappe tectonic system has become a boundary tectonic type of an active block supporting crustal deformation along the eastern margin of the Qinghai-Tibet Plateau from late Cenozoic till now. The Longriba fault zone is just an active faul

关键词： Qinghai-Tibet Plateau active block newly-generated fault zone slip rate nappe tectonics

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Late Quaternary Slip-rates and Slip Partitioning on the Southeastern Xianshuihe Fault System, Eastern Tibetan Plateau

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Acta Geologica Sinica(English Edition) 2016年第2期90卷 537-554页

作者： CHEN Guihua XU Xiwei wen xueze CHEN Yue-Gau Key Laboratory of Active Tectonics and Volcano Institute of Geology China Earthquake Administration Beijing 100029 China Earthquake Administration of Sichuan Province Chengdu 610041 Sichuan China Department of Geosciences National Taiwan University Taipei 10617 Taiwan China

Quantitative analysis of the kinematics of the active faults distributed around the QinghaiTibetan Plateau is critical to understand current tectonic processes of the plateau. Chronological analysis, based on the comparison among regional climate and geomorphology, digital photogrammetry, offset landforms, and the tectonics were adopted in this study on the Xianshuihe fault in the eastern Tibetan plateau. Two or more offset-age data were obtained for each segment of the Xianshuihe and theYunongxi faults. The offset landforms, including river terrace, alluvial fan and glacial moraine, provide constraints for the late Quaternary slip rate of the Xianshuihe fault. The left-lateral strike slip rate of the Xianshuihe fault decreases from 17 mm/a on the northwest segment to 9.3 mm/a on the southeast segment. Regarding the Xianshuihe fault zone and its adjacent blocks as a regional tectonic system, vector analysis was used to quantitatively analyze the longitudinal kinematical transformation and transversal slip partitioning on the fault zone in terms of the kinematical parameters of the main faults within the zone. The results show that there is a distributed vertical uplift at a rate of 6.1 mm/yr caused by shortening across the Gongga Mountains region. Based on these results, we established a model of the slip partitioning for the southeastern segment of the Xianshuihe fault zone.

关键词： slip partitioning kinematical transformation tectonic morphology Xianshuihe fault Gongga Mountains

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Assessment of time-dependent seismic hazards on segments of active fault, and its problems

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Chinese Science Bulletin 1998年第23期43卷 1937-1950页

作者： wen xueze Seismological Bureau of Sichuan Province, Chengdu 610041, China Seismological Bureau of Sichuan Province Chengdu China

Assessment of time dependent seismic hazards on segments of active fault is one of the important techniques of long term earthquake forecast for specific locations. It is based on the data from quantitatively seismo geologic investigation in active faults and expresses seismic hazards of a fault segment with both the earthquake occurrence probability, which increases as the elapsed time increases, and the magnitude predicted. Through summing up and analyzing main technical steps in research of the recent decade, some defects in the current theory and model of this technique are pointed out. For instance, the probabilistic models for recurrence interval are based solely on the quasi periodic behavior of earthquake recurrence, ignoring behavior’s diversity that possibly exists. Variability of repeated rupture dimensions in various cycles is considered inadequately in fault segmentation research, etc. It is most important for improving the reliability of the result of seismic hazard assessment to reveal actual earthquake recurrence behavior and its generalities, and to update relevant models for evaluating probabilistic earthquake hazard based on the behavior and generalities.

关键词： active fault rupture segmentation time dependent hazard probabilistic model long term forecast.

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Tectonic dynamics and correlation of major earthquake sequences of the Xiaojiang and Qujiang-Shiping fault systems, Yunnan, China

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Science China Earth Sciences 2011年第10期54卷 1563-1575页

作者： wen xueze DU Fang LONG Feng FAN Jun ZHU Hang Institute of Earthquake Science China Earthquake Administration Beijing 100036 China Earthquake Administration of Sichuan Province Chengdu 610041 China

The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjacent active fault systems and seismogenic zones associated with strong and major earthquakes in Yunnan, China. To understand the interaction of the two fault systems, and its probable influence on earthquake occurrences, this paper conducts a synthetic study based on data of active tectonics, historical earthquakes, relocated small earthquakes, GPS station velocities and focal mechanism resolutions. The study makes several conclusions. (1) The active southward motion of the western side of the Xiaojiang fault zone (i.e. the side of the Sichuan-Yunnan block) has a persistent and intensive effect on the Qujiang-Shiping fault zone. The later fault zone has absorbed and transformed the southward motion of the western side of the former fault zone through dextral strike-slip/shearing as well as transverse shortening/thrusting. (2) Along the Xiaojiang fault zone, the present sinistral strike-slip/shearing rate decreases from 10 and 8 mm/a on the northern, central and central-southern segments to 4 mm/a on the southern segment. The decreased rate has been adjusted in the area along and surrounding the Qujiang-Shiping fault zone through reverse-dextral faulting and distributed shearing and shortening. (3) The tectonic-dynamic relation between the Xiaojiang fault zone and the Qujiang-Shiping fault zone is also manifested by a close correlation of earthquake occurrences on the two fault zones. From 1500 to 1850 a sequence of strong and major earthquakes occurred along the Xiaojiang fault zone and its northern neighbor, the Zemuhe fault zone, which was characterized by gradually accelerating strain release, gradually shortening intervals between M≥7 events, and major releases occurring in the mid to later stages of the sequence. As a response to this sequence, after an 88-year delay, another sequence of 383 years (from 1588 to 1970) of strong and major earthquakes occurred on the Qujiang-Shiping fault zone, and had the same featu

关键词：小江断裂带地震序列构造动力学中国云南曲江故障系统应变能加速释放视屏

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NIR photosensitizers activated byγ-glutamyl transpeptidase for precise tumor fluorescence imaging and photodynamic therapy

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Science China Chemistry 2021年第5期64卷 808-816页

作者： Yingchao Chen xueze Zhao Tao Xiong Jianjun Du wen Sun Jiangli Fan Xiaojun Peng State Key Laboratory of Fine Chemicals Dalian University of TechnologyDalian 116024China Ningbo Institute of Dalian University of Technology Ningbo 315016China

Photodynamic therapy(PDT),a light triggered therapeutic mode,has been recognized as an attractive treatment for oncotherapy.The phototoxicity to normal tissues during treatment limited the development of PDT owing to the always“on”properties of photosensitizers.Activatable photosensitizers are of great importance for improving the selectivity of PDT.Herein,we regarded the overexpressed GGT(γ-Glutamyl transpeptidase)enzyme in tumor cells as a biomarker and developed an activatable photosensitizer Cy-GGT by decorating a specific recognition moiety of GGT,L-glutamic acid,to a hemicyanine dye based on photosensitizer Cy-NH_(2).Cy-GGT was in the“off”state with negligible fluorescence and suppressed singlet oxygen generation,but it could be specifically hydrolyzed to Cy-NH_(2) in the presence of GGT,accompanied with significant fluorescence recovery and singlet oxygen generation increase under light irradiation.The in vitro and in vivo studies indicated that Cy-GGT was suitable for precise tumor imaging and could work as an efficient photosensitizer for inhibiting tumor growth.

关键词： photodynamic therapy γ-glutamyl transpeptidase activatable fluorescence imaging

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Rupture segmentation and slip partitioning of the mid-eastern part of the Kunlun Fault,north Tibetan Plateau

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Science China Earth Sciences 2011年第11期54卷 1730-1745页

作者： LI ChenXia XU XiWei wen xueze ZHENG RongZhang CHEN GuiHua YANG Hu AN YanFen GAO Xiang Institute of Geology China Earthquake Administration National Center of Active Fault Studies Beijing 100029 China Lanzhou Seismological Institute of China Earthquake Administration Lanzhou 730000 China Earthquake Administration of Sichuan Province Chengdu 610041 China

The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part,both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau.New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers.Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset,new earthquake ruptures and surface-rupturing segmentation,from which long-term slip rates and earthquake recurrence intervals on the fault are estimated.The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu,Maqin and Maqu segments from west to east are 11.2±1,9.3±2,and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2,0.7±0.1,and 0.3 mm/a in the late Quaternary.Results indicate that the slip rates regularly decrease along the eastern ～300 km of the fault from >10 to <5 mm/a.This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault,which in turn is transformed to the Awancang Fault.The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode.The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°.The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A'nyêmaqên double restraining bend and the Xigongzhou intersection zone,which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthqu

关键词：青藏高原北部活动断裂带地震破裂分区模式东昆仑中东部分割地震复发间隔

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