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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 Ma- qu 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＇nyemaqen double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for t

关键词： mid-eastern Kunlun fault slip rate surface rupture segmentation slip partition paleoearthquake Tibetan Plateau

The M_S7.1 Yushu earthquake surface rupture and large historical earthquakes on the Garzê-Yushu fault

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Chinese Science Bulletin 2010年第31期55卷 3504-3509页

作者： CHEN LiChun WANG Hu RAN YongKang SUN XinZhe SU GuiWu WANG Ji TAN XiBin LI ZhiMin ZHANG XiaoQing National center for active fault Studies Institute of Geology China Earthquake Administration Beijing 100029 China China center for earthquake Disaster Prevention Beijing 100029 China earthquake Administration of Qinghai Province Xining 810001 China

As revealed by field investigations,the co-seismic surface rupture zone of the 2010 MS7.1 Yushu earthquake,Qinghai is a characteristic sinistral strike-slip feature consisting of three distinct sinistral primary ruptures,with an overall strike of 310°-320° and a total length of 31 *** addition,an approximately 2-km-long en-echelon tensile fissure zone was found east of Longbao Town;if this site is taken as the north end of the rupture zone,then the rupture had a total length of ～51 *** surface rupture zone is composed of a series of fissures arranged in an en-echelon or alternating relationship between compressive bulges and tensile fissures,with a measured maximum horizontal displacement of 1.8 *** surface rupture zone extends along the mapped Garzê-Yushu fault,which implicates it as the seismogenic fault for this ***,a few earthquakes with a magnitude of about 7 have occurred along the fault,and additionally traces of paleoearthquakes are evident that characterize the short-period recurrence interval of large earthquakes *** to the seismogenic process of the 2008 Wenchuan earthquake,the Yushu earthquake is also due to the stress accumulation and release on the block boundaries resulting from the eastward expansion of Qinghai-Tibet ***,in contrast with the Wenchuan earthquake,the Yushu earthquake had a sinistral strike-slip mechanism resulting from the uneven eastward extrusion of the Baryan Har and Sichuan-Yunnan fault blocks.

关键词：地震地表破裂地震对玉树历史断裂地表破裂带发震断层左旋走滑

Cenozoic Denudation and Vertical faulting History of the Central Segment of the Longmenshan Thrust Belt

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Acta Geologica Sinica(English Edition) 2016年第4期90卷 1541-1542页

作者： TAN Xibin XU Xiwei LEE Yuanhsi KANG Wenjun ZHAO Shiliang Key Laboratory of active fault and Volcano Institute of GeologyChina Earthquake Administration Department of Earth and Environmental Sciences National Chung-Cheng University

Objective The uplift process and uplift mechanism of the Tibetan Plateau has been a research focus among geologists in recent years. This work put emphasis on the Cenozoic exhumation histories of the blocks bounded by the major faults at the central segment of the Longmenshan thrust belt, and the vertical faulting history, including the starting time and the total vertical displacement, of the major faults. Then we quantitatively established a complete active process for the central segment of the Longmenshan thrust belt, combining with the previous geophysical data in the deep and geologcial data. This study is critical for deeply and completely understanding the Cenozoic uplift history of the Longmenshan, and also provides thermochronology constraints to the different models for the uplift of the eastern margin of the Tibetan Plateau.

关键词： Cenozoic Denudation and Vertical faulting History of the Central Segment of the Longmenshan Thrust Belt

Development of seismic force requirements for buildings in Taiwan

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earthquake Engineering and Engineering Vibration 2009年第3期8卷 349-358页

作者： Juin-Fu Chai Tsung-Jen Teng Keh-Chyuan Tsai center for research on earthquake Engineering

This paper describes static and dynamic procedures to calculate seismic demand specified by the current seismic design code for buildings in Taiwan, which was issued in 2005. For design levels with a return period of 475 years, the design spectral response acceleration can be developed for general sites, near-fault sites and Taipei Basin. In addition, in order to prevent building collapse during extremely large earthquakes and yielding of structural components and elements during frequent small earthquakes, the required seismic demands at the maximum considered earthquake level （MCE, 2%/50 years） and operational level are also included in the new seismic design *** dynamic analysis procedures, both the response spectrum method and time history method are specified in the new seismic design code. Finally, procedures to generate spectrum compatible ground motions for time history analysis are illustrated in this paper.

关键词： building code seismic force requirement design spectrum spectrum compatible design ground motion site effect near-fault basin effect

Discussion of rupture mechanisms on the seismogenic fault of the 2008 M_s8.0 Wenchuan earthquake

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Science China Earth Sciences 2011年第11期54卷 1360-1377页

作者： DENG QiDong CHEN GuiHua ZHU AiLan National center for active fault Studies Institute of Geology China Earthquake Administration Beifing 100029 China earthquake Administration of Shanghai Municipality Shanghai 200062 China

The May 12, 2008, Ms8.0 Wenchuan earthquake was the outcome of a recent movement of an active intra-continental thrust fault zone. The seismogenic fault of this earthquake underwent oblique-slip faulting along the central fault and pure thrust faulting along the range-front fault of the Longmenshan fault zone. The former had a steep dip and large vertical displacement, and the latter had a gentle dip and little vertical displacement. The fault zone consisted of compressive double fault ramps rup turing with right-lateral strike-slip components resulting from strain partitioning of a deep oblique slip fault in the brittle zone of the upper crust. The kinematic pattern and rupture mechanisms are complex for the seismogenic fault, as indicated by the geometric pattern of its surface ruptures, the coseismic displacement distribution and focal mechanisms of the main shock and aftershocks. As a tear fault, the NW-trending, left-lateral, strike-slip Xiaoyudong fault zone has accommodated NE-trending displacements with different shortening amounts. However, because of intense compression on the southwestern segment of the seismogenic fault, the left-lateral, strike-slip Xiaoyudong fault also carries a clear compression component. Normal faulting with a strike-slip component controls the formation of a fault-trough along the central fault, which is characterized by thrusting with a strike-slip component and strike-slip with thrusting. The fault-troughs are the product of the interaction of slip and grav ity on the seismogenic fault under specific geological and geomorphic conditions. Gravitational force exaggerated the vertical component of fault displacement, which by no means represents the actual maximum vertical displacement of the seismogenic fault.

关键词： Ms8.0 Wenchuan earthquake seismogenic fault rupture mechanism gravitation tear fault

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Internal structures and high-velocity frictional properties of Longmenshan fault zone at Shenxigou activated during the 2008 Wenchuan earthquake

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earthquake Science 2014年第5期27卷 499-528页

作者： Yu Wang Shengli Ma Toshihiko Shimamoto Lu Yao Jianye Chen Xiaosong Yang Honglin He Jiaxiang Dang Linfeng Hou Tetsuhiro Togo State Key Laboratory of earthquake Dynamics Institute of GeologyChina Earthquake Administration National center for active fault Studies Institute of GeologyChina Earthquake Administration earthquake Administration of Zhejiang Province Seismotectonics research Group Institute of Earthquake and Volcano GeologyNational Institute of Advanced Industrial Science and Technology

This paper reports internal structures of a wide fault zone at Shenxigou,Dujiangyan,Sichuan province,China,and high-velocity frictional properties of the fault gouge collected near the coseismic slip zone during the 2008 Wenchuan *** offset and horizontal displacement at the trench site were 2.8 m（NW side up）and 4.8 m（right-lateral）,*** fault zone formed in Triassic sandstone,siltstone,and shale about 500 m away from the Yingxiu-Beichuan fault,a major fault in the Longmenshan fault system.A trench survey across the coseismic fault,and observations of outcrops and drill cores down to a depth of 57 m revealed that the fault zone consists of fault gouge and fault breccia of about0.5 and 250-300 m in widths,respectively,and that the fault strikes N62°E and dips 68° to *** conglomerates were recovered beneath the fault in the drilling,so that the fault moved at least 55 m along the coseismic slip zone,experiencing about 18 events of similar *** fault core is composed of grayish gouge（GG） and blackish gouge（BG） with very complex slip-zone *** contains low-crystalline graphite of about 30 %.High-velocity friction experiments were conducted at normal stresses of 0.6-2.1 MPa and slip rates of 0.1-2.1 m/*** GG and BG exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient lpto steadystate friction coefficient lssover a slip-weakening distance *** of GG and BG is characterized by overlapped slip-zone structures and development of sharp slickenside surfaces,*** of our data with those reported for other outcrops indicates that the high-velocity frictional properties of the Longmenshan fault zones are quite uniform and the high-velocity weakening must have promoted dynamic rupture propagation during the Wenchuan earthquake.

关键词： Wenchuan earthquake - Longmenshan faultsystem - Shenxigou fault zone fault zone structures High-velocity friction

Wenchuan earthquake fault and seismic disaster

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earthquake Science 2009年第2期22卷 175-179页

作者： Boming Zhao Xiwei Xu School of Civil Engineering Beijing Jiaotong University Beijing 100044 China National center for active fault Studies Institute of Geology China Earthquake Administration Beijing 100029 China

Major cases of the Ms8.0 Wenchuan earthquake are obtained through field investigations of the epicenter and high-intensity areas, and the relationships among earthquake faults, ground motion and earthquake disasters near fault zones are analyzed. Both strong deformation and ground rupture lead to significant damages of the buildings, indicating that it is necessary to keep safe distance away from active faults and to take other necessary measures. There are two reasons for that the buildings near the surface rupture zones have withstood in the strong earthquake, other than their seismic resistance capacities, with the first being the site condition, and the second the reduced effective stress and low rupture velocity. The forms of structural damages are complex in the fault areas, with shear failure and tensile and compressive damages. Those structures in urban areas that have used qualified materials and followed the building codes performed well in the earthquake. Survey results also indicate that structures of flexible materials may show better seismic performance.

关键词： Wenchuan earthquake earthquake fault seismic disaster strong ground motion

Late Quaternary Large earthquakes on the Western Branch of the Xiaojiang fault and Their Tectonic Implications

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Acta Geologica Sinica(English Edition) 2015年第5期89卷 1516-1530页

作者： LI Xi RAN Yongkang CHEN Lichun WU Fuyao MA Xinquan CAO Jun Key Laboratory of active Tectonics and Volcano Institute of Geology China Earthquake Administration earthquake Administration of Yunnan Province

The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan *** largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral displacement of ~ 6.9 m, occurred on the western branch of the Xiaojiang *** this fault is important in understanding current deformation and kinematic characteristics of the Tibetan *** and stretches have been well undertaken on the Xiaojiang fault, while paleoseismic research work is always the weak link on this *** investigate the paleoseismic history and large earthquake activity of the Xiaojiang fault, we opened a large trench at the northern edge of Caohaizi sag pond on the western branch of the Xiaojiang *** paleoseismic events have been identified, and named E1 through E6 from the oldest to the *** and woods are abundant, 20 samples were dated to constrain the ages of the paleoseismic events at 40 000–36 300 BC, 35 400–24 800 BC, 9 500 BC–AD 500, AD 390–720, AD 1120–1620 and AD 1750–*** associate the youngest event E6 with the 1833 M8 *** E4, E5 and E6 show a continuous record of the western strand of the Xiaojiang fault in the late Holocene, with a average recurrence interval of 370–480 *** earthquake recurrence in the late Holocene is far less than the recurrence of 2000–4000 yr posed in previous ***, the seismic hazard on the Xiaojiang fault should be ***, the irregular recurrence of large earthquakes on the Xiaojiang fault and other faults in the Xianshuihe-Xiaojiang system, indicates the uneven southeastward extrusion of the Sichuan-Yunnan block along the southeastern margin of the Tibetan Plateau.

关键词： Xiaojiang fault sag pond large trench paleoearthquake recurrence interval Sichuan-Yunnan block

Complex Seismic Focus Structure and earthquake-Triggered Landslide Distribution:Analysis of the 2014 Ludian M_w6.1 earthquake in Yunnan

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Acta Geologica Sinica(English Edition) 2017年第2期91卷 733-734页

作者： CHEN Xiaoli LIU Chunguo Key Lab of active Tectonics and Volcano Institute of GeologyChina Earthquake AdministrationBeijing 100029China China earthquake Networks center Beijing 100045China

Objective The 2014 Ludian Mw6.1 earthquake in Yunnan occurred in a mountainous area with complex tectonics and topography, which caused serious damage as well as co-seismic landslides of an unusual large scale. Because the suspected seismogenic faults on the surface, distribution of aftershocks and focal mechanism solutions are not consistent, it remains difficult to determine what is the real causal fault or seismogenic structure for this event. Actually, it may imply the complicity of the seismic source at depth. In addition, the distribution of the co- seismic landslides also exhibits some diffusion that is different from general eases, likely associated with the seismic focus structure.

关键词： Complex Seismic Focus Structure and earthquake-Triggered Landslide Distribution:Analysis of the 2014 Ludian M_w6.1 earthquake in Yunnan