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Deep Seismogenic Environment in the Southern Section of the Longmenshan Fault Zone on the Eastern Margin of the Tibetan Plateau and Lushan M_s 7.0 earthquake

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Acta Geologica Sinica(English Edition) 2015年第2期89卷 519-530页

作者： LI Dahu DING Zhifeng ZHAN Yan WU Pingping YE Qingdong Institute of Geophysics China Earthquake Administration earthquake administration of sichuan Province Institute of Geology China Earthquake Administration

The 2,026 earthquake events registered by the sichuan regional digital seismic network and mobile seismic array after the April 20th, 2013 Lushan earthquake and 28,188 pieces of data were selected to determine direct P waves arrival times. We applied the tomographic method to inverse the characteristics of the velocity structure for the three-dimensional （3D） P wave in the mid-upper crust of the seismic source region of the Lushan earthquake. The imaging results were combined with the apparent magnetization inversion and magnetotelluric （MT） sounding retest data to comprehensively study the causes of the deep seismogenic environment in the southern section of the Longmenshan fault zone and explore the formation of the Lushan earthquake. Research has shown that there are obvious differences in velocity structure and magnetic distribution between the southern and northern sections of the Longmenshan fault zone. The epicenter of the Lushan earthquake is located near the boundary of the high and low-velocity anomalies and favorable for a high-velocity section. Moreover, at the epicenter of the Lushan earthquake located on the magnetic dome boundary of Ya＇an, the development of high velocity and magnetic solid medium favors the accumulation and release of strain energy. Low- velocity anomalies are distributed underneath the are of seismogenic origin, The inversion results of the MT retest data after the April 20th Lushan earthquake also indicate that there a high-conductor anomaly occurs under the area of seismogenic origin of the Lushan earthquake, Therefore, we speculated that the presence of a high-conductivity anomaly and low-velocity anomaly underneath the seismogenic body of the Lushan earthquake could be related to the existence of fluids. The role of fluids caused the weakening of the seismogenic layer inside the mid-upper crust and resulted in a seismogenic fault that was prone to rupture and pIayed a triggering role in the Lushan earthquake.

关键词： The Longmenshan fault zone Lushan earthquake the three-dimensional velocitystructure the apparent magnetization inversion magnetotelluric sounding

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Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

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Science China Earth Sciences 2023年第5期66卷 997-1014页

作者： Weilai WANG Guangyao CAI Guijuan LAI Xianwei ZENG Jingjing BAO Long ZHANG Jun SU Mingfei CHEN Institute of Geophysics China Earthquake AdministrationBeijing100081China earthquake Agency of Ningxia Hui Autonomous Region Yinchuan750001China sichuan earthquake Agency Chengdu610041China

A series of parallel normal faults are distributed in the Helan Mountain-Yinchuan Basin tectonic belt,where a historical M8.0 earthquake occurred.It is rare that such a great earthquake occurs in a normal fault system within the continent.To deeply understand the fine structure of the normal fault system,we deployed 104 broadband temporary stations near the system,collected data from permanent stations and other temporary stations nearby,and obtained the high-precision threedimensional S-wave velocity structure beneath 206 stations via joint inversion of receiver function and surface wave.A typical graben-in-graben feature bounded by four major faults was identified in the Yinchuan Basin.We analyzed the seismicity in the normal fault system and found a seismic strip in the southern part of the basin,where there are significant changes in the sedimentary thickness,which is speculated to be the southern boundary of the normal fault system.There are significant differences in the crustal thickness and velocity structure in the crust on both sides of the boundary between the Helan Mountain and the Yinchuan Basin,and a low-velocity zone was identified in the upper mantle beneath this boundary,which could be related to the fact that the Helan Mountain-Yinchuan Basin tectonic belt is located between the Alxa Block and the Ordos Block.The M8.0 Yinchuan-Pingluo earthquake occurred at the junction of four major faults in the Yinchuan Basin,which was located in the high-velocity zone near the velocity transition zone at the basin-mountain boundary.The low-velocity zone in the upper mantle beneath this boundary may have promoted the nucleation of this earthquake.Based on evidence from geological drilling,micro seismicity,the regional stress field,and the velocity models obtained in this study,it is inferred that the eastern piedmont fault zone of the Helan Mountain was the seismogenic fault of the 1739 M8.0 Yinchuan-Pingluo earthquake.

关键词： Yinchuan Basin Helan Mountain Receiver function Surface wave tomography Normal fault system

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Inventory and Spatial Distribution of Landslides Triggered by the 8th August 2017 M_W 6.5 Jiuzhaigou earthquake, China

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Journal of Earth Science 2019年第1期30卷 206-217页

作者： Yingying Tian Chong Xu Siyuan Ma Xiwei Xu Shiyuan Wang He Zhang Key Laboratory of Active Tectonics and Volcano Institute of GeologyChina Earthquake Administration Institute of Crustal Dynamics China Earthquake Administration sichuan earthquake Agency Hebei earthquake Agency

An accurate and detailed seismic landslide inventory is essential to better understand the landslide mechanism and susceptibility. The 8 th August 2017 MW 6.5 Jiuzhaigou earthquake of China initiated a large number of coseismic landslides. The results of the post-seismic survey show the actual landslide number might be underestimated in previous publications. Coupled with field investigation and visual interpretation on high-resolution remote sensing images before and after the main shock, we established a detailed inventory of landslides triggered by the earthquake. Results show that this event caused at least 4 834 individual landslides with a total area of 9.64 km^2. They are concentrated in an elliptical area of 434 km^2, dominated by medium-and small-scale rock falls and debris slides. Statistics indicate that, except for slope aspect that seems not significantly correlated with the landsliding, these landslides are most common in the places with following features: elevation of 2 800–3 400 m, slope angle greater than 30o, slope positions of upper, middle and flat slopes, and Carboniferous limestone and dolomite. Besides, the landslide area percentage(LAP) and landslide number density(LND) values decrease with the increasing distance to river channels and roads, implying a positive correlation. Instead of centering around the epicenter, most of these coseismic landslides are distributed along the inferred seismogenic fault, which means that the seismogenic structure played a more important role than the location of the epicenter. Remarkable differences in landslide densities along the fault indicate the varied landslide susceptibility which may be attributed to other varied controls along the fault such as the rock mass strength. In sum, this study presents a more detailed inventory of the landslides triggered by the 2017 MW 6.5 Jiuzhaigou earthquake, describes their distribution pattern and analyzes its control factors, which would be helpful to understand the genesis of the coseismic landslides and further

关键词： Jiuzhaigou earthquake coseismic landslide landslide inventory influencing factors spatial distribution

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Static Stress Triggering Effects Related with M_s8.0 Wenchuan earthquake

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Journal of Earth Science 2010年第1期21卷 32-41页

作者：朱航闻学泽 State Key Laboratory of earthquake Dynamics earthquake administration of sichuan Province Institute of earthquake Science China Earthquake Administration

In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induced by a sequence of strong earthquakes that occurred in Songpan （松藩）, sichuan （四川） Province in 1973 and 1976, and discovered that the Ms8.0 Wenchuan （汶川） earthquake of 2008 was epicentered in a relevant Coulomb stress triggering zone. This suggests that the Coulomb stress on the middle and southern segments of the Longmenshan （龙门山） fault zone increased after the Songpan sequence of strong earthquakes, and the stress increment might cause the 2008 Wenchuan earthquake having al- ready occurred somewhat ahead of time. Further, we calculated and analyzed Coulomb stress changes coinduced by both the Songpan sequence and the Ms8.0 Wenchuan mainshock. The result shows that the Ms6.4 Qingchuan （青川） earthquake of May 25, 2008 on the northeastern segment of the Longmenshan fault zone was triggered by the Wenchuan mainshock, and that the southwestern segment of the fault zone is also in the stress triggering zone. Besides, the Maoxian （茂县）-Wenchuan fault （i.e., the back-range fault of the Longmenshan fault zone）, which extends parallel to the seismogenic fault of the Wenchuan earthquake, is in a shadow zone of the Coulomb stress changes, and therefore, its potential hazard for producing a strong or large earthquake in the near future could be reduced relatively.

关键词： 2008 Wenchuan earthquake Songpan strong earthquake sequence static stress triggering Coulomb failure stress change seismic hazard.

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Relocation of the 2008 Panzhihua M_S6.1 earthquake Sequence

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earthquake Research in China 2015年第3期29卷 363-372页

作者： Fu Ying Long Feng earthquake administration of sichuan Province

The Panzhihua MS6. 1 earthquake sequence on August 30,2008 was relocated using the Hypo2000 + Hypo DD algorithm with the seismic phase data from the sichuan and Yunnan regional digital seismic networks,and the results show that the epicenters are distributed in the near NS direction,the length of aftershock concentration zone is about 30 km,and the main shock is about 14 km in depth. The depth of the sequence is distributed in the range of 0- 4km and 5- 20 km,and the layer of 4- 5km depth is an apparent earthquake absence layer. The cross-section along the fractures long axis shows there is an irregular seismic gap in the middle segment of the aftershock region,which is the rupture region of the M6 3/4 earthquake in 1955,and this earthquake occurred in the south of the gap. We believe that the Panzhihua MS6. 1 earthquake sequence on August 30,2008 was a result of rupture of the residual asperity caused by the stress adjustment of the Wenchuan MS8. 0 earthquake. The other two profiles perpendicular to the long axis show that the focal depth in the north segment is larger and the fault plane dips NW,which is consistent with the dip of the Hongge fault.

关键词：地震序列攀枝花区域数字地震台网震中分布深度分布地震发生应力调整震源深度

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Shear-wave splitting of sichuan Regional Seismic Network

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earthquake Science 2008年第2期21卷 127-138+219页

作者：张永久高原石玉涛程万正 earthquake administration of sichuan Province Institute of earthquake Science China Earthquake Administration

Using seismic data recorded by the Chengdu Digital Seismic Network from May 1, 2000 to December 31, 2006, we obtain the dominant polarization directions of fast shear-waves at eight digital seismic stations adopting the SAM technique. The results show that the dominant directions of polarizations of fast shear-waves at most of sta-tions are mainly in nearly NE-SW or NW-SE direction in sichuan. The dominant polarization directions of the fast shear-waves at stations located at the active faults or intersection of several active faults are consistent with the strikes of active faults which control the earthquakes used in the analysis, and are basically consistent with the directions of regional compression axis. However, several stations show that the fast shear-waves are not consis-tent with the strikes of active faults and the directions of regional compression axis, due to the influence of local complicated crustal structure.

关键词： shear-wave splitting polarization of fast shear-wave compression axis active fault sichuan region

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Preliminary results pertaining to coseismic displacement and preseismic strain accumulation of the Lushan M_S7.0 earthquake,as reflected by GPS surveying

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Chinese Science Bulletin 2013年第28期58卷 3460-3466页

作者： WU YanQiang JIANG ZaiSen WANG Min CHE Shi LIAO Hua LI Qiang LI Peng YANG YongLin XIANG HePing SHAO ZhiGang WANG WuXing WEI WenXin LIU XiaoXia CEA Key Laboratory of earthquake Prediction (Institute of earthquake Science) China Earthquake Administration State Key Laboratory of earthquake Dynamics Institute of GeologyChina Earthquake Administration China earthquake administration earthquake administration of sichuan Province National earthquake Infrastructure Service China Earthquake Administration

This paper presents the coseismic displacement and preseismic deformation fields of the Lushan MS7.0 earthquake that occurred on April 20,2013.The results are based on GPS observations along the Longmenshan fault and within its vicinity.The coseismic displacement and preseismic GPS results indicate that in the strain release of this earthquake,the thrust rupture is dominant and the laevorotation movement is secondary.Furthermore,we infer that any possible the rupture does not reach the earth’s surface,and the seismogenic fault is most likely one fault to the east of the Guanxian-Anxian fault.Some detailed results are obtainable.(1)The southern segment of the Longmenshan fault is locked preceding the Lushan earthquake.After the Wenchuan earthquake,the strain accumulation rate in the southeast direction accelerates in the epicenter of the Lushan earthquake,and the angle between the principal compressional strain and the seismogenic fault indicates that a sinistral deformation background in the direction of the seismogenic fault precedes the Lushan earthquake.Therefore,it is evident that the Wenchuan MS8.0 earthquake accelerated the pregnancy of the Lushan earthquake.(2)The coseismic displacements reflected by GPS data are mainly located in a region that is 230 km(NW direction)×100 km(SW direction),and coseismic displacements larger than 10 mm lie predominantly in a100-km region(NW direction).(3)On a large scale,the coseismic displacement shows thrust characteristics,but the associated values are remarkably small in the near field(within 70 km)of the earthquake fault.Meanwhile,the thrust movement in this70-km region does not correspond with the attenuation characteristics of the strain release,indicating that the rupture of this earthquake does not reach the earth’s surface.(4)The laevorotation movements are remarkable in the 50-km region,which is located in the hanging wall that is close to the earthquake fault,and the corresponding values in this case correlate with the attenuation characteristics of the strain re

关键词：地震发生同震位移 GPS测量应变积累庐山震前龙门山断裂带应变释放

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The strain seismograms of P- and S-waves of a local event recorded by four-gauge borehole strainmeter

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earthquake Science 2015年第3期28卷 209-214页

作者： Zehua Qiu Shunliang Chi Zhenming Wang Seth Carpenter Lei Tang Yanping Guo Guang Yang Institute of Crustal Dynamics China Earthquake Administration earthquake administration of Hebi Kentucky Geological Survey University of Kentucky Guza Seismic Station Earthquake Administration of Sichuan Province

At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters（FGBS） are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.

关键词： Four-gauge borehole strainmeter（FGBS） Strain seismogram P-wave S-wave Self-consistency Spectrum analysis

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

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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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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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