Risk Assessment of Disaster Chain: Experience from Wenchuan Earthquake-induced Landslides in China

This paper deals with the formative process of the Wenchuan earthquake disaster chain risk. Selected earthquake-landslides chain risk is critically evaluated by the probability of landslide displacement failure based on the Newmark's permanent-deformation model. In this context, a conceptual model of regional disaster chain risk assessment was proposed, in which the hazardformative environments sensitivity was the core factor as well as the main difference compared with single disaster risk assessment. The disaster chain risk is accumulation of primary disaster risk and the secondary disasters risks. Results derived from the Wenchuan case proved that the conceptual model was suitable for the disaster chain risk assessment, especially the sudden disaster chain. This experience would offer greater potential in application of conceptual model of disaster chain risk assessment, in the process of large-scale disaster risk governance.

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

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.

Vegetation Restoration Monitoring in Yingxiu Landslide Area after the 2008 Wenchuan Earthquake

A total of more than 50000 landslides has occurred in Sichuan province since the"5·12"Wenchuan earthquake,resulting in serious damage to the surface vegetation in southwestern China.In this study,we select Yingxiu,the epicenter of Wenchuan earthquake,as the experimental area.The vegetation coverage information of the experimental area is extracted from the remote sensing images collected in the year of 2005,2011 and 2013,respectively.The surface vegetation coverage in different periods is analyzed,and the vegetation recovery rate of the whole area is calculated.The experimental results show that in the first three years after the earthquake,the speed of vegetation restoration is slow,and the vegetation coverage rate is less than 20%better than 0.241,while in 2013,the vegetation coverage increases significantly.

The Spatial Distribution and Attribute Parameter Statistics of Landslides Triggered by the May 12th,2008,MW7.9 Wenchuan Earthquake

A complete landslide inventory and attribute database is the importantly fundamental for the study of the earthquake-induced landslide.Substantial landslides were triggered by the MW7.9 Wenchuan earthquake on May 12th,2008.Google Earth images of preand post-earthquakes show that 52194 co-seismic landslides were recognized and mapped,with a total landslides area of 1021 km2.Based on the statistics,we assigned all landslide parameters and established the co-seismic landslides database,which includes area,length,and width of landslides,elevation of the scarp top and foot edge,and the top and bottom elevations of each located slope.Finally,the spatial distribution and the above attribute parameters of landslides were analyzed.The results show that the spatial distribution of the co-seismic landslides is extremely uneven.The landslides that mainly occur in a rectangular area(a width of 30 km of the hanging wall of the Yingxiu-Beichuan fault and a length of 120 km between Yingxiu and Beichuan)are obviously controlled by surface rupture,terrain,and peak ground acceleration.Meanwhile,a large number of small landslides(individual landslide area less than 10000 m2)contribute less to the total landslides area.The number of landslides larger than 10000 m2 accounts for 38.7%of the total number of co-seismic landslides,while the area of those landslides account for 88%of the total landslides area.The 52194 co-seismic landslides are caused by bedrock collapse that usually consists of three parts:source area,transport area,and accumulation area.However,based on the area-volume power-law relationship,the resulting regional landslide volume may be much larger than the true landslide volume if the landslide volume is calculated using the influenced area from each landslide.

Changes in Runout Distances of Debris Flows over Time in the Wenchuan Earthquake Zone

A large number of debris flows occurred in the Wenchuan earthquake zone after the 12 May 2008 earthquake.The risks posed by these debris flows were rather high.An appropriate model is required to predict the possible runout distance and impacted area.This paper describes a study on the runout characteristics of the debris flows that occurred in the Wenchuan earthquake zone over the past four years.A total of 120 debris flows are analyzed.Separate multivariate regression models are established for the runout distances of hill-slope debris flows and channelized debris flows.The control variables include type of debris flow,debris flow volume,and elevation difference.Comparison of the debris flows occurring before and after the earthquake shows that the runout distance increased after the earthquake due to sufficient material supply and increased mobility of the source materials.In addition,the runout distances of annual debris flow events in 2008,2010 and 2011 are analyzed and compared.There is a tendency that the runout distance decreases over time due to the decreasing source material volume and possible changes of debris flow type.Comparison between the debris flows in the earthquake zone and the debris flows in Swiss Alps,Canada,Austria,and Japan shows that the former have a smaller mobility.

Forecast Method of Multimode System for Debris Flow Risk Assessment in Qingping Town,Sichuan Province,China

The Wenchuan Earthquake of May 12,2008 triggered large numbers of geo-hazards.The heavy rain on 13 August 2010 triggered debris flows with total volume of more than 6 million cubic meters and the debris flows destroyed 500 houses and infrastructure built after the Wenchuan Earthquake.The study area Qingping Town was located in the northwestern part of the Sichuan Basin of China,which needs the second reconstructions and the critical evaluation of debris flow.This study takes basin as the study unit and defines collapse,landslide and debris flow hazard as a geo-hazard system.A multimode system composed of principal series system and secondary parallel system were established to evaluate the hazard grade of debris flow in 138 drainage basins of Qingping Town.The evaluation result shows that 30.43% of study basins(42 basins) and 24.58% of study area,are in extremely high or high hazard grades,and both percentage of basin quantity and percentage of area in different hazard grades decrease with the increase of hazard grade.According to the geo-hazard data from the interpretation of unmanned plane image with a 0.5-m resolution and field investigation after the Wenchuan Earthquake and 8.13 Big Debris Flow,the ratio of landslides and collapses increased after the Wenchuan Earthquake and the ratios of extremely high or high hazard grades were more than moderate or low hazard grades obviously.23 geo-hazards after8.13 Big Debris Flow in Qingping town region all occurred in basins with extremely high or high hazard grades,and 9 debris flows were in basins with extremely high hazard grade.The model of multimode system for critical evaluation could forecast not only the collapse and landslide but also the debris flow precisely when the basin was taken as the study unit.

The formation of the Wulipo landslide and the resulting debris flow in Dujiangyan City, China

The Wulipo landslide, triggered by heavy rainfall on July 10, 2013, transformed into debris flow,resulted in the destruction of 12 houses, 44 deaths, and 117 missing. Our systematic investigation has led to the following results and to a new understanding about the formation and evolution process of this hazard. The fundamental factors of the formation of the landslide are a high-steep free surface at the front of the slide mass and the sandstone-mudstone mixed stratum structure of the slope. The inducing factor of the landslide is hydrostatic and hydrodynamic pressure change caused by heavy continuous rainfall. The geological mechanical model of the landslide can be summarized as "instability-translational slide-tension fracture-collapse" and the formation mechanism as "translational landslide induced by heavy rainfall". The total volume of the landslide is 124.6×104 m3, and 16.3% of the sliding mass was dropped down from the cliff and transformed into debris flow during the sliding process, which enlarged 46.7% of the original sliding deposit area. The final accumulation area is found to be 9.2×104 m2. The hazard is a typical example of a disaster chain involving landslide and its induced debris flow. The concealment and disaster chain effect is the main reason for the heavy damage. In future risk assessment, it is suggested to enhance the research onpotential landslide identification for weakly intercalated slopes. By considering the influence of the behaviors of landslide-induced debris flow, the disaster area could be determined more reasonably.

Retrospection on the Conclusions of Earthquake Tendency Forecast before the Wenchuan M_S8.0 Earthquake

The reason for the failure to forecast the Wenchuan Ms 8.0 earthquake is under study, based on the systematically collection of the seismicity anomalies and their analysis results from annual earthquake tendency forecasts between the 2001 Western Kunlun Mountains Pass Ms8. 1 earthquake and the 2008 Wenchuan Ms8.0 earthquake. The results show that the earthquake tendency estimation of Chinese Mainland is for strong earthquakes to occur in the active stage, and that there is still potential for the occurrence of a Ms8.0 large earthquake in Chinese Mainland after the 2001 Western Kuulun Mountains Pass earthquake. However the phenomena that many large earthquakes occurred around Chinese Mainland, and the 6-year long quietude of Ms7.0 earthquake and an obvious quietude of Ms5.0 and Ms6.0 earthquakes during 2002- 2007 led to the distinctly lower forecast estimation of earthquake tendency in Chinese Mainland after 2006. The middle part in the north-south seismic belt has been designated a seismic risk area of strong earthquake in recent years, but, the estimation of the risk degree in Southwestern China is insufficient after the Ning＇er Ms6.4 earthquake in Yunnan in 2007. There are no records of earthquakes with Ms ≥ 7.0 in the Longmenshan fault, which is one of reasons that this fault was not considered a seismic risk area of strong earthquakes in recent years.

基于遥感解译的典型强震区泥石流物源发育及演化--以四川都汶高速沿线为例

四川都汶高速位于2008年汶川地震强震区内,震后泥石流灾害异常活跃,对人类财产造成严重损失、人居安全构成重大威胁。为了查清山体斜坡物源空间分布规律,探讨汶川震区泥石流物源成因,选择区内震前DEM、震后Landsat TM多波段融合数据及典型泥石流沟2期全色波段遥感数据,进行泥石流物源发育特征及演化分析。结果表明:①汶川地震强震区物源发育受地形坡向、坡度、高程及水系的共同控制。在坡向上具有背坡面放大效应和逆冲(错动)方向放大效应,高程和坡度选择与山体斜坡发育的动力过程相关;②地震能量释放是物源发育基础,建立了强震区物源发育密度与地震烈度的指数关系模型,并认为研究区断层的存在可能促进了泥石流物源的进一步发育;③物源演化具有面积缩小、大型物源解体为多个小型物源、小型物源汇聚而致规模增大、物源迁移、出现新物源等特征。

不同特征选择方法于区域地震滑坡危险性预测结果的差异性分析——以汶川地震区为例

区域性地震滑坡危险性评估模型是一个用于评定特定地区在地震发生时滑坡概率及其危害程度的关键工具。目前,以机器学习为代表的数学建模方法成为了构建该评估模型的主要手段。但是,由于影响因子自身的复杂性与多样性所产生的评估模型预测结果的差异性这一问题却少有研究。此次研究结合汶川地震区内11个影响因子,分别运用相关性系数、主成分分析及Gini指数三种特征选择方法形成三类数据集。结合人工神经网络模型构建了该区域地震滑坡危险性评估模型,并详细地分析了上述三类方法形成的数据集构建的评估模型于预测结果的差异性。结果表明:基于主成分分析法形成的数据集构建的评估模型,对于非常高危险性等级区域的划分精度最高,并且,频率比精度达到了92%,ROC曲线的预测精度达到了93.3%,预测精度均为三组评估模型中的最高值。此次研究旨在为相关研究人员在地震滑坡危险性评估模型的构建方面提供一定的思路,并为后续综合多个地震区、多组特征组成的不同维度的数据集构建一个具有普适性的特征选择方法提供一定的理论基础。

2008年汶川地震滑坡详细编目及其空间分布规律分析

最新研究成果表明,2008年5月12日汶川MS8.0级地震触发了超过197000处滑坡。首先,基于GIS与遥感技术构建了汶川地震滑坡的3类编目图,分别为单体滑坡面分布数据、滑坡中心点位置和滑坡后壁点位置。构建方法为基于地震前后高分辨率遥感影像的目视解译方法,区分单体滑坡并圈定其边界,对滑坡后壁进行识别与定点,并开展了部分滑坡的野外验证工作。这些滑坡分布在一个面积大约为110000km2的区域内,滑坡总面积约为1160km2。选择一个面积约为44031km2的区域作为研究区,区内滑坡数量为196007个,滑坡面积为1150.622km2,这是最详细完整的汶川地震滑坡编录成果,也是单次地震事件触发滑坡最多的记录。其次,开展研究区内的地震滑坡空间分布规律的研究。基于滑坡面与滑坡中心点分别构建滑坡空间分布面积密度图与点密度图,结果表明:滑坡多沿着映秀—北川断裂分布,多发生在断裂的上盘。滑坡的高密度区位于"映秀—北川"同震地表破裂的南西段(映秀镇与北川县之间)的上盘区域,这一区域恰对应着逆冲分量为主的断裂上盘,表明逆冲断裂对上盘区域发生滑坡的极强烈的控制作用,而该区域正是形变最大的区域,因此说明是地震滑坡发生的强烈控制作用。基于滑坡面密度(LAP)、滑坡中心点密度(LCND)与滑坡后壁点密度(LTND)这3个衡量指标,使用统计分析方法,评价了汶川地震滑坡与地震参数、地质参数、地形参数的关系。结果表明:LAP、LCND与LTND这3个衡量指标与坡度、地震烈度与PGA存在明显的正相关关系;与距离震中、距离映秀—北川同震地表破裂存在负相关关系;斜坡曲率越接近0,滑坡越不易发生;LAP、LCND与LTND的高值高程区间为1200～3000m;滑坡发生的优势坡向为E、SE、S方向;滑坡发育的易发岩性为砂岩与粉砂岩(Z)、花岗岩;滑坡与坡位的相关关系不太明显。统计结果还表明LCND与LTND两个衡量指标的差异对地震与地质因子不敏感,而对地形因子较敏感。最后将本文的统计结果与以往的汶川地震滑坡空间分布规律统计成果进行了一些对比,对比结果表明,对于某些因子,如高程、岩性、距离震中、距离映秀—北川断裂的统计分析结果,采用不完整的滑坡分布数据或点数据,与采用较完整的滑坡分布面数据会有一定的差异,这种差异并未出现在针对坡度与坡向等因子的统计对比结果中。总之,作者认为一个完备、详细的地震滑坡分布面要素编目图是地震滑坡空间分布规律定量分析、危险性定量分析与滑坡控制的地震区地貌演化研究的重要基础,否则,与实际情况相比,得到统计结果会有一定的偏差,本文的研究成果与以往成果的对比结果证明了这一点。

“5·12”汶川地震崩塌滑坡危险性评价——以都汶公路沿线为例

选择地震极重灾区(都汶公路沿线)作为研究区域,利用遥感影像解译和野外调查数据,采用信息量方法,分析地震崩塌滑坡对影响因子的敏感性,结合GIS技术评价地震崩塌滑坡的危险性。研究表明,都汶公路沿线最利于地震崩塌滑坡的条件为:(1)坡度:大于35°;(2)坡向:E,ES和S坡向;(3)坡面粗糙度:大于1.15;(4)距断层距离:5～20km;(5)土地利用类型:林地、灌木林地和疏林地;(6)地层岩性:元古代闪长岩、元古代斜长花岗岩、元古界玄武岩、安山岩、石炭系灰岩、泥灰岩和志留系灰绿色千枚岩及石灰岩,尤其是元古界玄武岩和安山岩。利用信息量综合因子叠加技术,对研究区域崩塌滑坡体进行危险性评价,并将其分为极高度危险区、高度危险区、中度危险区、轻度危险区以及基本无危险区。危险性评价结果表明:研究区域大部分处于中度危险区、高度危险区、极高度危险区,三者面积占总面积的70.34%,其中极高度危险区占到总面积的19.15%,范围较大,在公路修复和重新规划建设中应加强预防这些区域发生崩塌滑坡;基本无危险区范围较小,仅占总面积的11.81%;在分布特征上,极高度危险区和高度危险区主要分布在映秀至草坡河段上,草坡河至汶川段大部分处于轻度危险区及以下。研究结果可为震后公路恢复、重建及灾区重建提供科学指导与技术支持。

地震堰塞湖排险技术与治理保护

"5.12"汶川特大地震形成了上百处堰塞体高度大于10 m,蓄水量大于1.0×105m3,集雨面积大于20 km2的堰塞湖。根据各类堰塞湖因对下游威胁程度、地质、地貌、水文条件、堰塞体规模和颗粒组成制定相应的排险方案。极高危和高危堰塞湖具有潜在的溃坝风险,必须及时排险。相对稳定的堰塞湖及其所在河道则应治理保护。结合北川唐家山、都江堰枷担湾等堰塞湖排险实例,提出了地震堰塞湖排险技术,包括险情勘查、险情评估、排险方案、施工技术。同时,对灾后堰塞湖观测、治理与保护利用提出了建议。

GIS支持下的地震诱发滑坡危险区预测研究

为了满足对地震诱发滑坡危险区预测的不断增长的迫切要求 ,灾害评价成为帮助决策过程重要的基础工具之一。即使地震滑坡危险性各组份的评价很困难 ,但地理信息可辅助提出这种灾害制图的有关方法。描述了用于地理信息系统识别和定量计算不同地震滑坡危险区的技术方法 ,确定了地震烈度、地形坡度、岩土体类型和现存滑坡密度共 4个因子参与的地震诱发滑坡危险性分析。在ARC/INFODRID支持下 ,进行叠合分析 ,由此编制了云南省地震诱发滑坡危险区预测图。由地貌学家提出的地震诱发滑坡预测为规划者和工程师提供了对区域规划和建筑工程有价值的技术方法。

汶川地震诱发滑坡灾害的数量与面积

2008年5月12日14时28分,以四川省汶川县为震中的地区发生了Ms8.0级大地震,地震造成了巨大的人员伤亡与财产损失,还诱发了数以万计的滑坡灾害。本研究基于震后航空像片与多源卫星遥感影像,辅以实地调查方法,在GIS平台支持下,对汶川地震诱发的滑坡灾害进行了解译调查工作。截至本文完成,在约48678km2的滑坡影响区域内,圈定了48007个地震诱发滑坡灾害,覆盖面积约711.8km2,这一数据远高于目前已经发表的结果。解译调查结果表明,汶川地震诱发滑坡类型多样,多沿发震断裂密集分布,形成多处地震堰塞湖。考虑到少部分地区遥感影像质量差且人员无法到达,估计汶川地震实际诱发滑坡数量超过50000个,覆盖面积约达750km2。全面客观地统计汶川地震诱发滑坡的数量与面积,对进一步研究地震滑坡空间分布、机理、评价预测,以及反推地震特征有着十分重要的意义。

汶川地震强震区地震诱发滑坡与后期降雨诱发滑坡控制因子耦合分析

本文以汶川地震强震区北川县典型研究区为例,利用高分辨率航片、SPOT5卫星图像对北川县典型研究区进行了"5.12"地震之后和"9.24"降雨之后诱发的滑坡解译,解译结果显示:"5.12"地震诱发滑坡1999个,"9.24"强降雨诱发滑坡828个,"9.24"强降雨导致原有地震滑坡面积扩大的滑坡150个。研究表明:地震和强降雨都是诱发滑坡的动力成因,"9.24"强降雨诱发的滑坡面积是"5.12"地震诱发滑坡面积的1/4倍,强降雨诱发滑坡的数量增加了41.4%;强降雨不仅诱发新的滑坡,而且促使原来地震滑坡复活,并扩大其面积,强降雨导致地震诱发的滑坡面积扩大了原面积的68.7%。同时,在遥感解译数据基础之上,开展地震诱发滑坡与降雨诱发滑坡规模对比和控制因子耦合分析及地震与降雨耦合灾害链模式研究,为进一步分析研究地震灾区滑坡的产生、发展趋势、危险性和风险评价等预测预报提供科学依据,也为汶川震区恢复重建中的减灾防灾提供决策参考。

汶川地震灾区滑坡风险区划研究

地震滑坡是在地震瞬间诱发的滑坡灾害。本文讨论了汶川地震灾区滑坡风险区划与常规滑坡风险区划的区别,认为地震滑坡风险区划应该在危险度区划中增加与地震相关的指标因子,如滑坡震中距和滑坡断层距。从而反映地震动能量对地震滑坡发育的贡献作用。而易损度区划中是难以体现地震因素作用的,这里采用滑坡密度、人口密度、道路密度、建筑物密度、耕地密度这5个指标进行易损度评价。最后采用权重叠加法进行了汶川地震极震区10个县市(面积26175.77km2)的滑坡风险区划,其中高、较高风险区分别占全区面积的9.03%和14.61%。说明震后灾区依然存在一定的滑坡风险。汶川地震极震区中,北川、青川、都江堰、彭州4地应该成为滑坡风险防御的主要地区。对滑坡风险区划结果进行了实地抽样检验,证明区划结果基本符合汶川极震灾区的情况。由此可见,本文介绍的地震滑坡风险区划方法是可靠的。

基于多变量统计分析的大型滑坡敏感性评价:以汶川地震影响的陇南地区为例

以"5.12"汶川地震影响较严重的甘肃东部的陇南震区为研究区,分析地震前后影响历史大型深层滑坡的空间要素,以专家经验分析确定的成因要素作为滑坡敏感性评价的初选方案。为了避免专家经验的客观性和要素相互重叠对滑坡敏感性评价的影响,执行主成分(PCA)多变量分析法以确定新的评价方案。2个方案分别通过逻辑回归模型(LR)执行,并绘制滑坡危险等级地图。采用成功率曲线和累积面积曲线对2种评价结果的有效性和性能进行检验和对比。检验结果表明:采用新方案所得的滑坡敏感性地图具有更好的性能和更高的精度,因此,新方案下由LR绘制的滑坡危险等级地图可作为指导研究区震后重建、基础设施建设和土地规划的依据。

地震滑坡危险性评估模型及初步应用

统计分析了汶川地震滑坡在不同影响因子下数量和密度,然后采用归一化方法确定影响地震滑坡的关键因子。基于关键因子建立了地震滑坡密度数学模型。结果表明：从滑坡数量看,滑坡主要集中在（10°-20°）至（40°-50°）的坡度（90 m栅格）区间,主体集中在35°附近,在3°-7°之间有一个滑坡分布的小峰值;滑坡密度随着坡度的增加而增加,在3°-7°的低坡地带有一个滑坡密度小峰值,在坡度一定的情况下,除了烈度外,其他影响因子下滑坡密度并没有表现出足够明显的规律性变化;归一化计算结果表明：坡度和烈度是地震滑坡的关键因子;根据逻辑斯蒂模型计算的结果,将地震滑坡危险性分为几无（≤0.01）、轻微（0.01-0.03）、中等（0.03-0.09）、严重（0.09-0.27）、特重（≥0.27）5个等级。地震滑坡危险性预测数据在鲁甸地震等地震应急中发挥了较好作用。

汶川地震前后都江堰山区滑坡滑动距离影响因素变化分析

滑坡滑动距离作为滑坡防灾减灾的主要评价指标之一,不仅受滑坡体积和落差的影响,还与滑坡运动的地质环境作用相关。本文在对都江堰地区51个地震滑坡、16个降雨滑坡详细调查编目的基础上,采用数理统计方法分析了斜坡原始坡度、滑坡前后缘高差、滑坡平面形态、体积、滑体平均厚度及坡面摩擦系数等6个因素与滑坡水平滑动距离的相关性,借此厘清了汶川Ms8.0级大地震前后不同因素对不同类型滑坡运动的贡献大小,进而构建了不同成因类型滑坡的滑动距离预测关系式,可为龙门山区的滑坡防灾减灾工作提供参考。研究表明:影响都江堰地区地震滑坡运动距离的主要因素有滑坡体积(lg V)、斜坡原始坡度(α)、滑坡平面形态(R)和滑坡前后缘高差(ΔH);而控制降雨滑坡运动距离的主要因素为滑坡前后缘高差(ΔH)、滑坡体积(lg V)、斜坡坡度(α)和斜坡表面摩擦系数(μ);汶川地震后,影响该地区降雨滑坡滑动能力的因素发生了变异,各因素与滑坡滑动距离的相关性较弱,显示出其贡献率在急剧减弱,仅滑坡体积(lg V)与滑动距离的相关性较强。