Table of Contents

Content
Chapter 1
Wenchuan-Earthquake Geohazards
汶川地震地质灾害
地质与构造背景 Geology and Tectonic Setting 8
地震概况 Earthquake Characteristics 10
地震灾情 Earthquake Emergency and Disaster Impact 12
地震滑坡制图 Mapping Earthquake-induced Landslides 14
地震滑坡分布控制因素分析 Analyzing Contributing Factors for Co-seismic Landslide Distribution 16
地震滑坡分布特征 Landslide Distribution Characteristics 18
地震诱发滑坡实例：北川县城 Earthquake-induced Landslides Example: Beichuan 20
大光包滑坡 Daguangbao Landslide 22
文家沟滑坡泥石流 Landslides and Debris Flows in Wenjia Gully 24
东河口滑坡 Donghekou Landslide 26
地震滑坡坝 Landslide Dams Induced by the Wenchuan Earthquake 28
滑坡坝溃坝模拟 Dam-breach Flood Simulation 30
滑坡坝敏感性评价 Earthquake-induced Landslide Dam Susceptibility Assessment 32
Chapter 2
Regional Scale Hazard and Risk Assessment
区域地质灾害危险性和风险评价
汶川县概况 Introduction to Wenchuan County 36
地震滑坡特征 Characteristics of Coseismic Landslides 38
映秀幅滑坡调查制图 Landslide Inventory Mapping for Yingxiu Map Sheet 40
映秀幅重点区滑坡调查制图 Landslide Inventory in Key Areas of Yingxiu Map Sheet 42
汶川幅滑坡调查制图 Landslide Inventory Mapping for Wenchuan Map Sheet 44
震后泥石流概况 Introduction of Post-earthquake Debris Flows 46
震后滑坡演化规律 Post-earthquake Landslide Development 48
滑坡敏感性分析 Analyzing Landslide Initiation Susceptibility 50
泥石流敏感性分析 Analysis of Debris Flow Susceptibility 52
交通设施暴露度分析 Exposure Analysis of Transportation Infrastructure 54
泥石流风险评价方法 Debris Flow Risk Assessment Method 56
泥石流暴露度及风险分析 Results of Exposure and Risk Analysis 58
Chapter 3
Local Scale Debris Flow Risk Assessment and Mitigation
大比例尺泥石流风险评价与控制
前言 Introduction 62
震后泥石流的影响 Impact of Post-earthquake Debris Flows 64
震后泥石流活动概况 Overview of Debris Flow Activities 66
多时相滑坡编目与制图 Multi-temporal Landslide Inventory 68
泥石流冲出规模预测 Estimation of Debris Flow Volumes 70
降雨重现周期推定 Rainfall Return Period Estimation 72
泥石流冲出模型 Debris Flow Runout Modelling 74
风险制图要素与易损性 Elements at Risk Mapping and Vulnerability 76
泥石流风险定量评价 Debris Flow Risk Assessment 78
降雨阈值推定 Rainfall Threshold Estimation 80
泥石流早期预警系统设计 Design of Debris Flow Early Warning Systems 82
泥石流防治工程效益分析 Cost-benefit Analysis of Debris Flow Mitigation 84
泥石流综合防治工程措施：文家沟 Debris Flow Mitigation Measures: Wenjia Gully 86
泥石流综合防治工程措施：烧房沟 Debris Flow Mitigation Measures: Shaofang Gully 88
References and Publications
参考文献和出版物
参考文献 References 92
出版物 Publications 94

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Geology and Tectonic Setting
The Longmen Mounain range is a region of steep relief between the eastern Tibetan Plateau and the Sichuan Basin (Figure 1.1). The Indian continental plate is subducting northward at a rate of 5–5.5 cm/a， affecting Tibet and the surrounding region. This causes strong compressional deformation， associated with crustal shortening， followed by an E-W crustal extension in the Late Miocene to Quaternary (Figure 1.1).
The present-day Longmen Mountain region is roughly coincident with the position of a Mesozoic collisional plate margin that developed during the closure of the Paleo-Tethys and the collision of the Qiangtang block with the North China-Kunlun-Qaidam and South China blocks (Li et al.， 2003). Wang and Meng (2009) stated that the Longmen Mountain fault belt was first formed as an intercontinental transfer fault， partitioning the differential deformation between the Pacific and Tethys tectonic domains， initiated in the Late Paleozoic—Early Mesozoic period and continued to the Late Cretaceous. From the northwest to southeast， the eastern margin of the Tibetan Plateau is composed of three major tectonic units: the Songpan-Ganzi Fold Belt， the Longmen Mountain Thrust Belt， and the Longmen Mountain Foreland Basin (Li et al.， 2003). The south-eastward extrusion of the Songpan-Ganzi block， which obliquely collided with the foreland basin， resulted in three large thrust faults in the Longmen Mountain tectonic boundary: the Wenchuan-Maoxian fault， the Yingxiu- Beichuan fault and the Pengzhou-Guanxian fault (Wang and Meng， 2009) (Figure 1.2). These faults accommodated significant crustal shortening during the Late Triassic Indosinian Orogeny (Li et al.， 2003)， which has led to the identification of the Longmen Mountain region as a major thrust zone that was reactivated in the India-Asia collision (Xu and Kamp， 2000). During the collision， a complex package of rocks， including Triassic marine sedimentary rocks of the Songpan-Ganzi remnant ocean basin (Zhou and Graham， 1996)， was thrust to the southeast over the margin of the South China block， creating a Late Triassic foreland basin.
The Wenchuan earthquake (Mw 7.9) occurred on 12 May 2008 (USGS， 2008) in the Longmen Mountain region at the eastern margin of the Tibetan Plateau， adjacent to the Sichuan Basin. The earthquake， with a focal depth of 14 km to 19 km， initiated close to the base of the Yingxiu-Beichuan fault and propagated upwards. Seismological data indicate that the rupture initiated in the southern Longmen Mountain and propagated unilaterally toward the northeast， along a northwest dipping fault for about 320 km (Xu et al.， 2009). It was felt as far as Beijing (1，500 km) and Shanghai (1，700 km)， and tall office buildings in those cities shook with the tremor. The earthquake was also felt in nearby countries. The earthquake ruptured both the Yingxiu-Beichuan (about 240 km long) and Pengzhou-Guanxian faults (72km long)， which are linked by a short northwest striking rupture zone at the southern end surface rupture through a lateral ramp. The largest surface slip (about 11.0 m vertical and 4.5 m right-lateral displacement) is found near Beichuan County (Liu et al.， 2009).
After the earthquake， extensive tectonic research was carried out in the eastern margin of the Plateau (Jin et al.， 2009; Zhang et al.， 2009; Tang et al.， 2009; Wang and Meng， 2009). Densmore et al. (2007) and Li et al. (2003)， indicated that the Longmen Mountain fault zone represents the features of thrusting and dextral strike-slip in the Late Cenozoic. The dextral strike-slip rate of the Yingxiu-Beichuan fault since the Late Pleistocene is less than 1 mm/a， and the thrust rate is 0.3—6 mm/a. Such low slip rates are consistent with GPS estimates of the shortening rate across the Longmen Mountain range of <3 mm/a (Shen et al.， 2009; Xu et al.， 2009).
Figure 1.1 Tectonic structure of western China and surroundings (Jia et al.， 2010).
Figure 1.2 Left: General tectonic map of the Longmen Mountain region. AF. Anninghe fault; BF. Yingxiu-Beichuan fault. HF: Huya fault; QF. Qingchuan fault; SF. Shimian fault; WMF. Wenchuan-Maoxian fault; XF. Xianshuihe fault; XSF. X