近远震作用下黄土滑坡动力响应与变形——以甘肃天水震区黎坪村滑坡为例

中国黄土高原区地震滑坡灾害效应重、潜在风险高,地震滑坡响应和变形机理是研究热点之一。以天水震区黎坪村大型黄土滑坡为例,采用标准正弦波探讨了近远震地震动要素对滑坡动力响应的影响特征,采用汶川远震和岷县近震地震动时程记录反演了滑坡实际变形特征。结果显示,测点PGA放大系数随振幅的变化规律与坡体位置有关,测点PGA放大系数在坡体位置大于0.75倍坡高时,随振幅的增加而减小;当小于0.75倍坡高时,随振幅的增加而显著增强;测点PGA放大系数与频率变化呈负相关性,即随着频率的增加而减小。坡体变形与振幅和持时变化呈正相关性,即测点最大水平和竖直位移随着振幅和持时增加而增加,滑坡急剧变形的临界幅值约为0.05 g;坡体变形与频率变化呈负相关性,坡体测点最大水平和竖直位移随频率变大呈下降趋势,滑坡急剧变形临界频率约为5 Hz;对比分析显示,振幅对坡体失稳的影响程度大于频率的影响程度。相比岷县近震,坡体主滑体滑动与汶川远震产生的高幅值、低频率及长持时的地震波作用密不可分,表明在地震滑坡稳定性研究时,如果忽视远场强震影响,可能导致潜在安全风险。关于近震和远震作用下滑坡动力响应及其变形差异研究方法对地震滑坡稳定性分析研究具有借鉴意义。     

汶川、芦山和鲁甸地震滑坡分布规律对比研究

汶川M_S8.0级地震、芦山M_S7.0级地震和鲁甸M_S6.5级地震均引发了大量的滑坡灾害。由于震级差异和地质地形条件的不同,地震滑坡分布情况有较大区别。本文综合已有的研究成果,从地震、地质和地貌3个方面,对比分析了地震滑坡的分布规律。结果表明:（1）3次地震滑坡数量和密度随着PGA和震级的增加而增加。汶川和鲁甸地震随烈度的增加,滑坡数量呈现递增的趋势。但芦山地震在较低烈度区也发育着大量滑坡。（2）断层影响滑坡分布的最大距离随着震级的增加而增加。在最大影响距离0.2倍的范围内,汶川地震分布有80%的滑坡,而其他两次地震仅30%。此外,汶川地震滑坡数量随断层距离呈指数衰减关系。（3）地震滑坡的分布受到地形的强烈影响。Ⅶ度及以上烈度区地形切割深度越大,地震触发的滑坡集中分布区域相对高差越大。同时,滑坡集中发育的坡度会随之增加。切割深度越大,地震滑坡更易发生在地势较陡的山脊或者上坡处,这可能与地形放大效应有关。     

Statistical analysis of landslides caused by the Mw 6.9 Yushu,China, earthquake of April 14, 2010

The April 14, 2010 Yushu, China, earthquake (Mw 6.9) triggered a great number of landslides. At least 2,036 co-seismic landslides, with a total coverage area of 1.194 km², were delineated by visual interpretation of aerial photographs and satellite images taken following the earthquake, and verified by field inspection. Based on the mapping results, a statistical analysis of the spatial distribution of these landslides is performed using the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides, and landslide number density (LND), defined as the number of landslides per square kilometer. The purpose is to clarify how the landslides correlate the control factors, which are the elevation, slope angle, slope aspect, slope position, distance from drainages, lithology, distance from the surface rupture, and peak ground acceleration (PGA). The results show that both LAP and LND have strongly positive correlations with slope angle and negative correlations with distance from the surface rupture and distance from drainages. The highest LAP and LPD values are in places of elevations from 3,800 to 4,000 m. The slopes producing landslides are mostly facing toward NE, E, and SE. The geological units of Q₄ al-pl, N, and T₃ kn ¹ have the highest concentrations of co-seismic landslides. No apparent correlations are present between LAP and LND values and PGA. On both sides of the surface rupture, the landslide distributions are almost similar except a few exceptions, likely associated with the nature of the strike-slip seismogenic fault for this event. The bivariate statistical analysis shows that, in descending order, the earthquake-triggered landslide impact factors are distance from surface rupture > slope angle > distance from drainages > lithology > PGA. Besides, as the detailed co-seismic landslides inventories related to strike-slip earthquakes are still few compared with that of thrusting-fault earthquakes, this case study would shed new light on the subject. For instance, the landslide spatial distribution on both sides of the strike-slip seismogenic fault is rather different from that of thrusting-fault earthquakes. It reminds us to take different strategies of measures for prevention and mitigation of landslides induced by earthquakes with different mechanisms.     

Spatial distribution analysis and susceptibility mapping of landslides triggered before and after Mw7.8 Gorkha earthquake along Upper Bhote Koshi,Nepal

The 2015 Mw7.8 Gorkha earthquake triggered thousands of landslides of various types scattered over a large area. In the current study, we utilized pre- and post-earthquake high-resolution satellite imagery to compile two landslide inventories before and after earthquake and prepared three landslide susceptibility maps within 404 km² area using frequency ratio (FR) model. From the study, we could map about 519 landslides including 178 pre-earthquake slides and 341 coseismic slides were identified. This study investigated the relationship between landslide occurrence and landslide causative factors, i.e., slope, aspect, altitude, plan curvature, lithology, land use, distance from streams, distance from road, distance from faults, and peak ground acceleration. The analysis showed that the majority of landslides both pre-earthquake and coseismic occurred at slope >30°, preferably in S, SE, and SW directions and within altitude ranging from 1000 to 1500 m and 1500 to 3500 m. Scatter plots between number of landslides per km^?2 (LN) and percentage of landslide area (LA) and causative factors indicate that slope is the most influencing factor followed by lithology and PGA for the landslide formation. Higher landslide susceptibility before earthquake is observed along the road and rivers, whereas landslides after earthquake are triggered at steeper slopes and at higher altitudes. Combined susceptibility map indicates the effect of topography, geology, and land cover in the triggering of landslides in the entire basin. The resultant landslide susceptibility maps are verified through AUC showing success rates of 78, 81, and 77%, respectively. These susceptibility maps are helpful for engineers and planners for future development work in the landslide prone area.     

Impact of seismic factors on landslide susceptibility zonation: a case study in part of Indian Himalayas

Landslides are one of the most widespread natural hazards in high mountain terrains such as the Himalayas, which are one of the youngest tectonically and seismically active mountain ranges in the world. The crustal movements along the longitudinal thrusts and transverse faults give rise to earthquakes and in turn initiate landslides in the region. In fact, in addition to various static factors causing landslides, earthquakes are one of the major causes of landslides. It is thus imperative to incorporate seismic factor also while carrying out landslide susceptibility zonation map preparation in a seismically active areas like Garhwal Himalayas. In this paper, a study on the effect of earthquakes on landslide susceptibility zonation has been demonstrated by taking Chamoli earthquake as an example.     

Earthquake triggered landslide–Indian scenario

Landslide initiation due to earthquake is one of the most prevalent seismic hazard, which claims hundreds of lives in the Himalayan mountainous terrains of India. Number of landslides, maximum distance from the epicentre and total landslide area/volume are correlatable with earthquake magnitudes. Application of globally accepted earthquake triggered landslide parameter models do not match well with published data for the Himalayan earthquake triggered landslides. Considering the incompleteness of landslide inventories for most of the Himalayan earthquakes, development of regression equations show that in the Himalayan environment, landslide may trigger even with imperciptable earthquakes affecting longer distances having earthquake magnitude of more than 8 M with potential to affect more areas than the global expectations.     

走滑断裂型地震诱发的滑坡在断裂两盘的空间分布差异

以玉树地震滑坡为实例,选择高程、坡度、坡向、坡位、水系、地层岩性、同震地表破裂、地震动峰值加速度(PGA)8个因子,以地震滑坡面积百分比(LAP)与滑坡点密度(LND)为指标,研究走滑断裂型地震诱发滑坡在断裂两盘的空间分布差异。在分析这些影响因子的断裂两盘的差异的基础上,基于LAP与LND两个指标详细分析断裂两盘每个因子内部级别滑坡发育的情况。结果表明,总体上北盘的滑坡较南盘发育,除了个别因子级别内南北盘滑坡差别较大外,大部分表现为南北盘滑坡分布情况类似。总之,玉树地震滑坡在断裂两盘的空间分布基本类似,只是在某些因子分级内存在一定的差异。     

走滑断裂型地震诱发的滑坡在断裂两盘的空间分布差异

以玉树地震滑坡为实例,选择高程、坡度、坡向、坡位、水系、地层岩性、同震地表破裂、地震动峰值加速度(PGA)8个因子,以地震滑坡面积百分比(LAP)与滑坡点密度(LND)为指标,研究走滑断裂型地震诱发滑坡在断裂两盘的空间分布差异。在分析这些影响因子的断裂两盘的差异的基础上,基于LAP与LND两个指标详细分析断裂两盘每个因子内部级别滑坡发育的情况。结果表明,总体上北盘的滑坡较南盘发育,除了个别因子级别内南北盘滑坡差别较大外,大部分表现为南北盘滑坡分布情况类似。总之,玉树地震滑坡在断裂两盘的空间分布基本类似,只是在某些因子分级内存在一定的差异。     

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MS 8.0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。     

GIS支持下基于CF方法的2013年芦山地震滑坡因子敏感性分析

本文依据研究区现有地形因子(高程、坡度、坡向、斜坡曲率)、地质因子(岩性、距深大活动断裂距离)和地震因子(PGA、距震中距离)等相关影响因子资料并结合地震区基本情况,以GIS技术作为操作平台,采用确定性系数法,开展较为详细的芦山地震区地震滑坡影响因子敏感性分析工作。首先,以GIS技术作为操作平台将地震滑坡的8个影响因子据研究区特征进行分级,构建不同影响因子分级的栅格图层进行地震滑坡分布相关参数统计; 其次,采用确定性系数法计算8个地震滑坡影响因子分级区间对应的CF值,分别提取出地震滑坡最为敏感分级区间以进行地震滑坡影响因子敏感性分析,从而衡量不同影响因子分级区间对地震滑坡易发性敏感程度。地震滑坡影响因子敏感性分析结果表明,除斜坡曲率因子与距震中距离因子对地震滑坡易发性不敏感外,其他6个影响因子对地震滑坡易发性均很敏感,分别是影响滑坡发生的主要地形、地质和地震因子。针对斜坡曲率因子和距震中距离因子对滑坡的易发性不是很敏感是否受内部其他影响因子限制所进行的分析与讨论结果表明,SW向很可能限制了斜坡曲率对地震滑坡易发性的敏感程度,地层岩性对距震中距离因子限制作用更为明显,除奥陶系、志留系外的地层岩性对距震中距离因子敏感性程度都有限制。文章所得成果具有一定的方法理论意义,对于防震减灾工作也具有一定参考意义。     

Influence of seismic acceleration on landslide susceptibility maps: a case study from NE Turkey (the Kelkit Valley)

Particularly in the last decade, landslide susceptibility and hazard maps have been used for urban planning and site selection of infrastructures. Most of the procedures for preparing of landslide susceptibility maps need high-quality landslide inventory map. Although the rainfall and seismic activities are accepted as triggering factor for landslides, designation of the triggering factor for each landslide in the inventory is almost impossible when well-documented records are unavailable. Therefore, during preparation of landslide susceptibility map, whole landslide records in the inventory map are used together without classifying based on the triggering factors. Although seismic activity is accepted as a triggering factor, possible effect of the use of seismic activity on production of landslide susceptibility map was investigated in this study, and the subject is open to discussion. For this purpose, a series of stability analyses based on circular failure and infinite slope model were performed considering different pseudostatic conditions. The results of analyses show that gentle slopes have higher susceptibility to failure than steeper ones, even if their stability conditions (susceptibilities) are similar for static condition. The seismic forces acting on failure surfaces may not be sufficiently taken into consideration in the conventionally prepared landslide susceptibility maps. Employing the general decreasing trend in stability condition based on slope face angle and the seismic acceleration, a new procedure was introduced for preparing of the landslide susceptibility map for a scenario earthquake. The prediction performance of occurring landslides increased after the procedure was applied to the conventionally prepared landslide susceptibility map. According to the threshold independent spatial performance analyses of the proposed methodology and the produced landslide susceptibility maps, the area under ROC curve values were calculated as 0.801, 0.933, and 0.947 for the maps prepared by considering conventional method and scenario earthquakes having M _w values of 5.5 and 7.5, respectively.     

基于GIS与ANN模型的地震滑坡易发性区划

基于遥感数据、地理信息系统(GIS)技术和人工神经网络(ANN)模型,开展地震滑坡易发性区划研究.2010年4月14日玉树地震后,基于航片与卫星影像目视解译,并辅以野外调查的方法,在地震区圈定了2036处地震诱发滑坡.选择高程、坡度、坡向、斜坡曲率、坡位、与水系距离、地层岩性、与断裂距离、与公路距离、归一化植被指数(NDVI)、与同震地表破裂距离、地震动峰值加速度(PGA)共12个因子作为地震滑坡易发性评价因子.这些因子均是应用GIS技术与遥感影像处理技术,基于地形数据、地质数据、遥感数据得到.训练样本中的滑动样本有两组,一组是滑坡区整个单滑坡体的质心位置,另一组是滑坡滑源区滑前的坡体高程最高的位置.应用这12个影响因子,分别采用这两组评价样本,基于ANN模型建立地震滑坡易发性索引图,基于GIS工具建立地震滑坡易发性分级图.分别应用训练样本中滑坡分布的点数据去检验各自的结果正确率,正确率分别为81.53％与81.29％,表明ANN模型是一种高效科学的地震滑坡易发性区划模型.     

Do landslides follow landslides? Insights in path dependency from a multi-temporal landslide inventory

Landslides are a major category of natural disasters, causing loss of lives, livelihoods and property. The critical roles played by triggering (such as extreme rainfall and earthquakes), and intrinsic factors (such as slope steepness, soil properties and lithology) have previously successfully been recognized and quantified using a variety of qualitative, quantitative and hybrid methods in a wide range of study sites. However, available data typically do not allow to investigate the effect that earlier landslides have on intrinsic factors and hence on follow-up landslides. Therefore, existing methods cannot account for the potentially complex susceptibility changes caused by landslide events. In this study, we used a substantially different alternative approach to shed light on the potential effect of earlier landslides using a multi-temporal dataset of landslide occurrence containing 17 time slices. Spatial overlap and the time interval between landslides play key roles in our work. We quantified the degree to which landslides preferentially occur in locations where landslides occurred previously, how long such an effect is noticeable, and how landslides are spatially associated over time. We also investigated whether overlap with previous landslides causes differences in landslide geometric properties. We found that overlap among landslides demonstrates a clear legacy effect (path dependency) that has influence on the landslide affected area. Landslides appear to cause greater susceptibility for follow-up landslides over a period of about 10  years. Follow-up landslides are on average larger and rounder than landslides that do not follow earlier slides. The effect of earlier landslides on follow-up landslides has implications for understanding of the landslides evolution and the assessment of landslide susceptibility.     

俯冲带地区压扭断裂型地震触发滑坡及其剥蚀厚度空间分布规律分析

2010年1月12日海地MW 7.0级地震触发了大量的滑坡。我们基于GIS与遥感技术构建了3类详细完备的海地地震滑坡编录图,分别为单体滑坡面分布数据,滑坡中心点位置数据与滑坡后壁点位置数据。结果表明海地地震触发了30828处滑坡,这些滑坡大致分布在一个面积为3192.85km2的区域内,滑坡覆盖面积为15.736km2。基于滑坡中心点密度(LCND)、滑坡后壁点密度(LTND)、滑坡面积百分比(LAP)与滑坡剥蚀厚度(LET)这4个衡量指标,使用统计分析方法,分析了海地地震滑坡及其剥蚀厚度与地震参数、地形参数、公路参数的关系。分析结果表明滑坡与坡度、地震动峰值加速度(PGA)存在大致的正相关关系; 与距离恩里基约芭蕉园断裂、距离水系存在大致的负相关关系; 滑坡沿着恩里基约芭蕉园断裂距离的统计结果表明,震中以西距离震中22~26km与8~12km的区域,与震中以东距离震中6~18km的区域是地震滑坡易发区域; 斜坡曲率值越接近0,也就是坡面较平的斜坡越不容易在地震条件下发生滑动; LCND、LTND、LAP与LET高值对应的高程区间为200~1200m; 滑坡发生的优势坡向为E方向; 滑坡的发生与距离震中、距离公路没有太明确的关系。     

Application of an analytical hierarchical process approach for landslide susceptibility mapping in A Luoi district,Thua Thien Hue Province,Vietnam

A Luoi is a Vietnamese–Laotian border district situated in the western part of Thua Thien Hue province, central Vietnam, where landslides occur frequently and seriously affect local living conditions. This study focuses on the spatial analysis of landslide susceptibility in this 263-km² area. To analyze landslide manifestation in the study area, causative factor maps are derived of slope angle, weathering, land use, geomorphology, fault density, geology, drainage distance, elevation, and precipitation. The analytical hierarchical process approach is used to combine these maps for landslide susceptibility mapping. A landslide susceptibility zonation map with four landslide susceptibility classes, i.e. low, moderate, high, and very high susceptibility for landsliding, is derived based on the correspondence with an inventory of observed landslides. The final map indicates that about 37% of the area is very highly susceptible for landsliding and about 22% is highly susceptible, which means that more than half of the area should be considered prone to landsliding.     

四川汶川Ms 8 级地震引发的滑坡与地层岩性、坡度的相关性

震后遥感影像解译与调查结果表明,在大约48678km2的区域内,汶川Ms 8.0级地震诱发了不低于48000处滑坡灾害。基于GIS的空间分析方法,使用滑坡面积百分比(LAR)与滑坡密度(LC)2个参数,对地震滑坡的空间分布与地层岩性、坡度之间的关系进行统计分析。在整个研究区范围内,滑坡面积百分比约为1.4622%,滑坡密度约为0.9862个/km2。结果表明,滑坡多发生在坡度25~50°的区域内,滑坡易发性随着坡度的增加而升高。寒武纪地层中滑坡易发性最大,LAR约10%,LC约6.5个/km2,震旦系、奥陶系和侵入岩次之,这些地层和岩石对地震滑坡的发生均是敏感的。综合分析坡度、地层岩性与滑坡空间分布的关系,结果表明,在以较破碎岩石为主的地层中,滑坡多发生在坡度小于30°的部位;在以较坚硬岩石为主的地层中,滑坡多发生在坡度大于40°的部位。     

Susceptibility assessments of the Wenchuan earthquake-triggered landslides in Longnan using logistic regression

In this study a Wenchuan earthquake-induced landslide susceptibility assessment was carried out in the Longnan area in northwestern China using a GIS-based logistic regression model. This region has frequently been affected by landslides in the past, and was intensively affected by the 5.12 Wenchuan earthquake which received considerable international attention. The data used for this study consist of the landslides triggered by the Wenchuan earthquake and a landslide pre-disposing factor database. Information regarding the landslide causative factors came from additional data sources, such as a digital elevation model (DEM) with a 30 × 30 m² resolution, orthophotos, geological and land-use maps, precipitation records, and information on peak ground acceleration data from the 2008 earthquake. The statistical analysis of the relationship between the Wenchuan earthquake-triggered landslides and pre-disposing factors showed the great influence of lithological and topographical conditions on slope failures. The quality of susceptibility mapping was validated by splitting the study area into training and validation sections. The prediction capability analysis demonstrated that the landslide susceptibility map could be used for land planning as well as emergency planning by local authorities.     

秦岭北麓古滑坡分布特征与地震活动关系研究

地震滑坡是严重的次生地质灾害,也是改变地球表层地貌形态的重要力量,对地震诱发滑坡的规模、数量、类型等研究是地震危险性评价的重要手段,也是认识地震地质灾害的主要方法和途径。位于西安市以南的秦岭山脉北麓中段发育有一条长约50 km的古滑坡群,且基本与山前秦岭北缘断裂带平行展布,普遍认为该古滑坡群可能是由于秦岭北缘断裂的强震活动所诱发,但对于诱发地震的震级大小和影响范围尚没有细致研究。本文通过利用资源3号卫星立体影像制作的高分辨率数值高程模型(DEM)和高分辨率多光谱遥感影像对秦岭北麓古滑坡区域进行了详细的解译工作,并结合对部分古滑坡体进行了野外调查,制作了详细秦岭北麓古滑坡分布图。结果表明:解译出了43处古滑坡,主要集中分布在70 km×10 km的范围内,总滑坡面积是16.57 km2。通过利用地震震级与滑坡面积频度分布的关系分析了诱发秦岭北麓古滑坡群的地震规模,得到了诱发秦岭北麓古滑坡群的地震震级应在7.6~8.1之间。并结合区域地震构造环境以及与现代地震诱发滑坡事件的对比,认为秦岭北麓具有发生7.5级以上地震的潜在能力。该研究对认识现今秦岭北麓古滑坡的成因提供了定量化的数据支持,也对理解秦岭北缘断裂的地震危险性具有重要的现实意义。     

Pre-conditioning factors and susceptibility assessments of Wenchuan earthquake landslide at the Zhouqu segment of Bailongjiang basin, China

In this study, we present a landslide susceptibility assessment carried out after the devastating 2008 Wenchuan earthquake. For the Zhouqu segment in the Bailongjiang basin in north-western China landslide susceptibility was computed by a logistic regression method. This region has been experiencing landslides for a long time, and numerous additional slope failures were triggered by the 2008 Wenchuan earthquake. The data used for this study consists of slope failures attributed to the 2008 earthquake, the 878 post Wenchuan earthquake landslides and collapses inventory build up by combination the field investigation, monoscopic manual interpretation, image classification and texture analysis using SPOT 5 and ALOS remote-sensing image data. All data derived from remote sensing images are validated during field investigations. The landslide pre-disposing factor database was constructed. A digital elevation model (DEM) with a 30 × 30 m resolution, orthophotos, geological and land-use maps and information on peak ground acceleration data from the 2008 earthquake is used. The statistical analysis of the relation between Wencuan earthquake-triggered landslides and pre-disposing factors show the great influence of lithological and topographical conditions for earthquake-triggered slope failures. The quality of susceptibility mapping was validated by splitting the study area into a training and validation set. The prediction capability analysis showed that the landslide susceptibility map could be used for land planning as well as emergency planning by local authorities in this region.     

Spatial distribution of landslides triggered by the 2008 Ms 8.0 Wenchuan earthquake,China

The Ms 8.0 Wenchuan earthquake of May 12, 2008 is one of the most disastrous earthquakes in China. The earthquake triggered tens of thousands of landslides over a broad area, including shallow, disrupted landslides, rock falls, deep-seated landslides, and rock avalanches, some of which buried large sections of some towns and dammed the rivers. The purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions, and seismic parameters. Over 56,000 earthquake-triggered landslides, with a total area of 811 km², are interpreted using aerial photographs and remote sensing images taken following the earthquake. The spatial distribution of these landslides is analyzed statistically using both landslide-point density (LPD), defined as the number of landslides per square kilometer, and landslide-area density (LAD), the percentage of the area affected by landslides, to determine how the occurrence of landslides correlates with distance from the epicenter, distance from the major surface rupture, seismic intensity and peak ground acceleration (PGA), slope angle, slope aspect, elevation, and lithology. It is found that both LAD and LPD have strong positive correlations with slope steepness, distance from the major surface rupture and seismic intensity, and that Pre-Sinian schist, and Cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities, followed by the Permian limestone intercalated with shale, and Devonian limestone. Statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides, because LAD and LPD are relatively higher on the hanging wall than on the footwall. However, the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated, rather than a relatively simple negative correlation as found from other reported cases of earthquakes. This is possibly due to complicated rupture processes of the earthquake.