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High-velocity frictional behavior of Longmenshan fault gouge from Hongkou outcrop and its implications for dynamic weakening of fault during the 2008 Wenchuan earthquake

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earthquake Science 2011年第3期24卷 267-281页

作者： Tetsuhiro Togo Toshihiko Shimamoto Shengli Ma Takehiro Hirose 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 Kochi Institute for Core Sample Research Japan Agency for Marine-Earth Science and Technology ( JAMSTEC) 200 Monobe-otsu Kochi 783-8502 Japan

High-velocity friction experiments were conducted on clayey fault gouge collected from Hongkou outcrop of Beichuan fault, located at the southwestern part of Longmenshan fault system that caused the disastrous 2008 Wenchuan earthquake. The ultimate purpose of this study is to reproduce this earthquake by modeling based on measured frictional properties. Dry gouge of about 1 mm in thickness was deformed dry at slip rates of 0.01 to 1.3 m/s and at normal stresses of 0.61 to 3.04 MPa, using a rotary-shear high-velocity frictional testing machine. The gouge displays slip weakening behavior as initial peak friction decays towards steady-state values after a given displacement. Both peak friction and steady-state friction remain high at slow slip rates are exam- ined and gouge only exhibits dramatic weakening at high slip rates, with steady-state friction coefficient values of about 0.1 to 0.2. Specific fracture energy ranges from 1 to 4 MN/m in our results and this is of the same order as seismically determined values. Low friction coefficients measured on experimental faults are in broad agree- ment with lack of thermal anomaly observed from temperature measurements in WFSD-1 drill hole （Wenchuan earthquake Fault Scientific Drilling Project）, which can be explained by even smaller friction coefficient for the Wenchuan earthquake fault. High-velocity friction experiments with pore water needs to be done to see if even smaller friction is attained or not. Shiny slickenside surfaces form at high slip rates, but not at slow slip rates. Slip zone with slickenside surface changes its color to dark brown and forms duplex-like microstructures, which are similar to those microstructures found in the fault gouges from the Hongkou outcrop. Detailed comparisons between experimentally deformed gouge samples and WFSD drill cores in the future will reveal how much we could reproduce the dynamic weakening processes in operation in fault zones during Wenchuan earthquake at present.

关键词： Wenchuan earthquake high-velocity friction fault mechanics Longmenshan fault system Beichuan fault

Transient postseismic slip and aftershock triggering:A case study of the 2008 M_W7.9 Wenchuan earthquake,China

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earthquake Science 2023年第6期36卷 445-457页

作者： Mengyu Xie Baoping Shi Lingyuan Meng China earthquake Networks Center Beijing 100045China College of Earth Sciences University of Chinese Academy of SciencesBeijing 100049China

In this study,we investigate how a stress variation generated by a fault that experiences transient postseismic slip(TPS)affects the rate of aftershocks.First,we show that the postseismic slip from Rubin-Ampuero model is a TPS that can occur on the main fault with a velocity-weakening frictional motion,that the resultant slip function is similar to the generalized Jeffreys-Lomnitz creep law,and that the TPS can be explained by a continuous creep process undergoing reloading.Second,we obtain an approximate solution based on the Helmstetter-Shaw seismicity model relating the rate of aftershocks to such TPS.For the wenchuan sequence,we perform a numerical fitting of the cumulative number of aftershocks using the Modified Omori Law(MOL),the Dieterich model,and the specific TPS model.The fitting curves indicate that the data can be better explained by the TPS model with a B/A ratio of approximately 1.12,where A and B are the parameters in the rate-and state-dependent friction law respectively.Moreover,the p and c that appear in the MOL can be interpreted by the B/A and the critical slip distance,respectively.Because the B/A ratio in the current model is always larger than 1,the model could become a possible candidate to explain aftershock rate commonly decay as a power law with a p-value larger than 1.Finally,the influence of the background seismicity rate r on parameters is studied;the results show that except for the apparent aftershock duration,other parameters are insensitive to r.

关键词： transient postseismic slip(TPS) Modified Omori Law(MOL) p-value rate-and state-dependent friction law Wenchuan earthquake

Emergency assessment of seismic landslide susceptibility: a case study of the 2008 Wenchuan earthquake affected area

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earthquake Engineering and Engineering Vibration 2009年第2期8卷 207-217页

作者： Tang Chuan,Zhu Jing and Liang Jingtao State Key Laboratory of Geo-Hazard Prevention,Chengdu University of Technology,Chengdu 610059,China Professor Associate Professor Graduate Student Professor State Key Laboratory of Geo-Hazard Prevention Chengdu University of Technology Chengdu 610059 China. Associate Professor State Key Laboratory of Geo-Hazard Prevention Chengdu University of Technology Chengdu 610059 China. State Key Laboratory of Geo-Hazard Prevention Chengdu University of Technology Chengdu 610059 China

The 8.0 Mw Wenchuan earthquake triggered widespread and large scale landslides in mountainous regions. An approach was used to map and assess landslide susceptibility in a given area. A numerical rating system was applied to five factors that contribute to slope instability. Factors such as lithology, topography, streams and faults have an important influence as event-controlling factors for landslide susceptibility assessment. A final map is provided to show areas of low, medium, and high landslide susceptibility. Areas identified as having high landslide susceptibility were located in the central, northeastern, and far south regions of the study area. The assessment results will help decision makers to select safe sites for emergency placement of refuges and plan for future reconstruction. The maps may also be used as a basis for landslide risk management in the study area.

关键词： landslide susceptibility GIS Wenchuan earthquake Qingchuan area

Suitability evaluation of population and settlements spatial layout after Wenchuan earthquake

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Journal of Geographical Sciences 2011年第3期21卷 539-548页

作者： FANG Chuanglin WU Fenglin LI Maoxun Institute of Geographic Sciences and Natural Resources Research CAS Beijing 100101 China China Tourism Academy Beijing 100005 China

The suitability evaluation of population and settlements spatial layout in the mountainous areas is an important basis on which the scale of population and settlement after Wenchuan earthquake is determined. Based on the statistical data of field research, this paper chooses 1264 towns in 51 counties as the scope of evaluation, selects eight indices in the evaluation index system which includes post-disaster population scale, population density, urbanization rate, the percentage of migrant workers, death rate by earthquake, the percentage of minorities, elevation-slope integrated terrain and comprehensive geological condition. Besides, this paper uses AHP supported by entropy technique and fuzzy membership function model to calculate the suitability evaluation index and then divides the disaster areas into five types： highly suitable area （area accounted for 11.03%）, relatively highly suitable area （15.29%）, moderately suitable area （29%）, less suitable area （30.08%） and unsuitable area （14.6%）. According to the result of suitability evaluation, this paper puts forward several suggestions for the reconstruction as follows： the urban system and the building of new countryside should be guided by the suitability evaluation subareas; post-earthquake reconstruction avoids zones near Longmenshan fracture and high-mountain gorge areas as far as possible; the scale of population and settlement should not exceed the capacity of resources and environment; population should be resettled as close as possible by considering adequately the heterogenicity and homogeneity of regional nationality culture characteristics; densely resettle the people at plains and hilly areas; encourage the migrant workers settle in the working place with their families voluntarily; and urban system reconstruction such as industry layout and important projects of lifeline should be guided by the spatial layout suitability evaluation.

关键词： suitability evaluation spatial layout Wenchuan earthquake post-earthquake

Analysis of landslide damage caused by the 2008 Wenchuan earthquake using strong motion data: A case study in the Beichuan county town

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earthquake Science 2012年第4期25卷 307-313页

作者： Xiuying Wang Gaozhong Nie Song Wang Institute of Crustal Dynamics China Earthquake Administration Institute of Geology China Earthquake Administration China earthquake Networks Center

The county town of Beichuan county, China, experienced catastrophic destruction due to landslides induce by the 2008 Wenchuan earthquake. In consideration of the special location of the county town, this paper selected the landslides induced in the town as representative of large-scale near-rupture landslides, and quantitatively analyzed why the landslide damage was so destructive in the town by using strong motion data obtained from the Wenchuan earthquake in the Longmenshan area. Three methods were employed to estimate the landslide damage using strong motion data. （1） Peak ground accelerations （PGAs） on the hanging wall were used to evaluate the PGAs on the landslide sites in the town. The evaluated average PGAs were all greater than I g, indicating that the ground motion intensity was very strong during the earthquake. （2） Acceleration time histories, from another station with similar geological conditions to the town, were used to evaluate the critical acceleration changing range, and the estimated values showed the geological conditions were very susceptible to earthquakes. （3） Acceleration time histories, from two stations on the hanging and foot walls of the rupture, and near the town, were used to calculate the Newmark displacements, and all the evaluated displacements indicated that landslides were very likely. The results show that the slopes, susceptible to earthquakes in the Beichuan county town, were easily triggered under such strong ground-motion intensity and developed into large-scale catastrophic events.

关键词： Wenchuan earthquake landslide strong motion evaluation critical acceleration

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

Characteristics of Landslides Induced by the Great Wenchuan earthquake

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Journal of Earth Science 2010年第1期21卷 104-113页

作者：唐辉明贾洪彪胡新丽李德威熊承仁 Faculty of Engineering China University of Geosciences Faculty of Earth Sciences China University of Geosciences

The great wenchuan （汶川） earthquake induced a large quantity of landslides. They are widely distributed and caused tremendous damages. The sliding mechanism and characteristics of these earthquake-induced landslides are different from those of conventional gravity landslides. Their occurrences are apparently controlled by the powerful earthquake, and they are characterized by high potential energy sliding and ejection sliding. In this article, the earthquake-induced landslides are classified, the characteristics of the sliding and destruction of these landslides are described, and the rela- tionship between the earthquake and the landslides is analyzed. The Donghekou （东河口） landslide is used as an example to characterize fast-moving long-distance earthquake-induced ejection slippage and landslide. This research suggests that many phenomena and issues related to earthquake-induced land- slide are beyond current recognition and knowledge, and new methodologies should be adopted to consider the effect of the earthquake as the paramount factor in the development of landslides. Furthermore, the study of fast-moving long-distance earthquake-induced landslides can also shed light on the formation of old and ancient landslides.

关键词： Wenchuan earthquake giant landslide ejection landslide high potential energy land- slide.

Shear wave velocity-based liquefaction evaluation in the great Wenchuan earthquake: a preliminary case study

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earthquake Engineering and Engineering Vibration 2009年第2期8卷 231-239页

作者： Zhou Yanguo,Chen Yunmin and Ling Daosheng MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering,Institute of Geotechnical Engineering,Zhejiang University,Hangzhou 310058,China Assistant Professor Professor Assistant Professor MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Institute of Geotechnical Engineering Zhejiang University Hangzhou 310058 China. Professor MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Institute of Geotechnical Engineering Zhejiang University Hangzhou 310058 China

The great Wenchuan earthquake （Ms= 8.0） in 2008 caused severe damage in the western part of the Chengdu Plain. Soil liquefaction was one of the major causes of damage in the plain areas, and proper evaluation of liquefaction potential is important in the definition of the seismic hazard facing a given region and post-earthquake reconstruction. In this paper, a simplified procedure is proposed for liquefaction assessment of sandy deposits using shear wave velocity （V）, and soil liquefaction from the Banqiao School site was preliminarily investigated after the earthquake. Boreholes were made at the site and shear wave velocities were measured both by SASW and down-hole methods. Based on the in-situ soil information and V profiles, the liquefaction potential of this site was evaluated. The results are reasonably consistent with the actual field behavior observed after the earthquake, indicating that the proposed procedure is effective. The possible effects of gravel and fines contents on liquefaction of sandy soils were also briefly discussed.

关键词： liquefaction Wenchuan earthquake shear wave velocity spectral analysis of surface waves （SASW） hazarddefinition

Damage investigation of girder bridges under the Wenchuan earthquake and corresponding seismic design recommendations

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earthquake Engineering and Engineering Vibration 2008年第4期7卷 337-344页

作者： Li Jianzhong Peng Tianbo Xu Yan State Key Lab for Disaster Reduction in Civil Engineering Tongji University Shanghai 200092 China

An investigation of girder bridges on National Highway 213 and the Doujiangyan-wenchuan expressway after the Wenchuan earthquake showed that typical types of damage included： span collapses due to unseating at expansion joints; shear key failure; and damage of the expansion joint due to the slide-induced large relative displacement between the bottom of the girder and the top of the laminated-rubber bearing. This slide, however, can actually act as a form of isolation for the substructure, and as a result, the piers and foundation of most of the bridges on state route 213 suffered minor damage. The exception was the Baihua Bridge, which suffered severe damage. Corresponding seismic design recommendations are presented based on this investigation.

关键词： Wenchuan earthquake bridge damage investigation seismic design recommendation