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.

The Critical Rainfall Characteristics for Torrents and Debris Flows in the Wenchuan Earthquake Stricken Area

Critical rainfall assessment is a very important tool for hazard management of torrents and debris flows in mountainous areas. The Wenchuan Earthquake 2008 caused huge casualties and property damages in the earthquake-stricken area,which also generated large quantities of loose solid materials and increased occurrence probabilities of debris flows. There is an urgent need to quantify the critical rainfall distribution in the area so that better hazard management could be planned and if real time rainfall forecast is available,torrent and debris flow early-warning could be issued in advance. This study is based on 49-year observations (1954-2003) of up to 678 torrent and debris flow events. Detailed contour maps of 1 hour and 24 hour critical rainfalls have been generated (Due to the data limitation,there was insufficient 10 minute critical rainfall to make its contour map). Generally,the contour maps from 1 hour and 24 hours have similar patterns. Three zones with low,medium and high critical rainfalls have been identified. The characteristics of the critical rainfall zones are linked with the local vegetation cover and land forms. Further studies and observations are needed to validate the finding and improve the contour maps.

Territorial suitability assessment and function zoning in the Jiuzhaigou earthquake-stricken area

An earthquake in the Jiuzhaigou area caused numerous secondary disasters, such as rolling stones, land collapse, landslides and debris flow, which badly affected the safety of human settlements and influenced the spatial layout of the post-disaster reconstruction. Therefore, carrying out assessments of land and identifying a suitable zone for human habitats were very important. This research creates the territorial suitability assessment and function zoning conceptual model in the earthquake-stricken area, and the new methods of the territorial suitability evaluation system were used to divide the spatial functional zones of the earthquake stricken area, which provide a theoretical guidance and decisionmaking basis for the reconstruction of the disaster area. The results showed that:(1) The Jiuzhaigou earthquake-stricken area comprises of an ecological area that has a high level of importance to the ecosystem. In the earthquake-stricken area, 65% of national land is at an altitude of 3000-4000 m, and therefore not suitable for a high level of intensive reconstruction, but reconstructed in an eco-friendly manner.(2) The zone suitable for reconstruction comprises mainly of the river valley and the flat terrain of western parts. The land with low suitability is mainly located on steep terrain, such as highmountains and low gullies. The geographic and geomorphic conditions limit the spread of a suitable reconstruction zone.(3) The earthquake-stricken area mainly comprises of a tourism industry gathering area, population gathering area, agriculture and animal husbandry development area, and ecological preservation area with areas of 76 km^2, 44 km^2, 1591 km^2 and 7512 km^2, respectively. Scientifically zoning the reconstruction areas using scientific evaluation may provide guidance for the location of reconstruction sites.

Evaluation of a traditional method for peak flow discharge estimation for floods in the Wenchuan Earthquake area,Sichuan Province,China

Peak discharge of flood in small mountainous watershed is usually calculated using the "Rainstorm–runoff calculation method in small watersheds in Sichuan Province"(RRM). This study evaluated the RRM calculation using real-time monitored rainfall and hydrologic data from a small watershed in the Wenchuan Earthquake area of Sichuan Province, China. The results indicated that the discharge values given by the RRM are commonly overestimating the measured discharge. The overestimation rate was discussed and empirical equations were proposed for improving RRM estimations, based on the relationship between calculated and measured discharge values at different watershed scales(2, 30, and 40 km2), under different rainfall probabilities(0.97–0.5, 0.5–0.2, and 0.2–0.002), and for different rainfall durations(0–6, 6–24, and >24 h). The results of this study help contribute to the understanding of water floods formation and help provide more accurate estimations of peak flow discharge in small watersheds in the Wenchuan Earthquake 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.

E-commerce Development Strategies of Agriculture-related Enterprises in Earthquake Area

The problems existing in the development of agriculture-related enterprises in earthquake area are evaluated,as well as the prominent issues existing in the process of developing E-commerce,consequently,the corresponding strategies for developing E-commerce in agriculture-related enterprises are proposed.

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.

Three-dimensional crustal deformation before and after the Wenchuan earthquake in Guanzhong and adjacent regions

The recent plethora of GPS observations compensates for the 20-year-old lack in vertical displacement data for the Guanzhong region. The 2001—2007 three-dimensional（3D） crustal deformation data suggest regional movement with a horizontal velocity of 3—7 mm/a,predominantly from SSE in the west to SE in the east, and vertical inherited movement with velocity of -7 mm/a to 4 mm/a. After the Wenchuan earthquake, the GPS data suggest that the effect of the earthquake on the regional deformation is greater in the west than the east.The horizontal displacement increased during 2007—2008; however, the reverse was observed in 2008—2009. The vertical displacement in the western part of the region increased in 2008 and has been gradually returning to normal since 2009; however, in the eastern part,the effect of the earthquake remains.

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.

汶川震区山洪灾害场次洪水最大携沙量预测模型

汶川地震后,震区产生了大量松散堆积体,受强降水影响产生了破坏性更强的山洪灾害,加剧了灾害的危险性,增加了灾害防治的困难度,研究震区山洪灾害可为评估灾害的风险性及后续的管理提供依据。本研究以66处历史山洪灾害作为样本数据,进行可量算影响因子的相关性分析,揭示山洪灾害的携沙量影响机制,确定流域面积、主沟长度、相对高差、物源量四个影响因子作为主控因子,基于SPSS进行非线性回归分析,建立了基于场次洪水最大携沙量及最大携沙距离的估算模型,并选取了汶川县和都江堰市的共23处山洪水沙灾害数据进行了模型的验证且与其他模型对比。结果表明,本研究建立的模型可靠性好,精度更高。研究成果有助于预测汶川震区潜在的山洪水沙灾害区域,为山洪水沙灾害的风险评估提供依据。

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。

基于非线性回归的暴雨泥石流堵河预测

堵河型泥石流灾害在汶川震区较为常见,其链式灾害效应严重威胁到了区域内人民的生命财产安全。故准确预测泥石流堵河程度,并采取相应的防治措施是至关重要的。以四川省绵竹市清平镇于2010年8月13日暴发的群发性泥石流为研究对象,通过分析因子权重,利用非线性回归建立了泥石流堵河程度的预测模型,并与已有模型进行了对比,论证了所建立模型的可用性,其后对不同降雨频率下的泥石流堵河程度进行预测。结果表明:流量比和流域面积是最佳的建模因子,所建立的模型绝对平均误差为0.049;与不同模型对比发现本文模型对于清平镇泥石流堵河预测具有很好的适用性;在极端降雨下,部分沟道堵河预测程度为1,会造成绵远河堵断。研究成果可为该地区泥石流灾害的防治和治理提供参考。

四川汶川—茂县河谷地区土地质量地球化学评价

对四川汶川—茂县河谷地区优选耕地区开展了土地质量地球化学评价工作,结果表明,研究区土壤环境质量总体以无风险土壤为主,占研究区总面积的95.47%。土壤养分总体呈丰富和较丰富状态,仅磷和钾在局部地区较缺乏;土壤环境质量整体良好;研究区土壤质量以优质土壤为主,占研究区总面积的86.69%;研究区绿色食品产地、绿色富硒土地资源较丰富,分别有4971.7和238.3 hm^(2)。土地质量地球化学评价成果对土地利用、规划布局、发展现代农业、耕地保护等方面具有重要指导意义。

5．12汶川地震中山区公路桥梁震害及启示

通过对5.12汶川地震强震区桥梁震害调查,总结了此次地震中桥梁、特别是山区公路桥梁在地震中破坏形态和特点,初步揭示此次地震造成桥梁(特别是山区公路桥梁)的破坏原因和特点,为灾区地震损伤桥梁的抗震加固和重新建造桥梁提供一些参考,同时初步分析了震害原因和应从中吸起的一些教训,为今后桥梁抗震设计提供合理建议.

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。

汶川震区银厂沟区域8·18暴雨泥石流灾害成灾机理与特征

2012年8月18日汶川震区的银厂沟区域暴发群发性泥石流,造成人员伤亡,公路、房屋等基础设施严重受损。这场泥石流灾害发生在汶川地震极震区内,是地震与强降雨共同作用下的结果,因此研究其成灾机制和灾害特征对于进一步认识强震区泥石流活动具有重要意义。本研究采用地面调查和遥感解译方法,分析银厂沟区域泥石流形成条件的变化。研究结果表明强震条件下崩塌、滑坡等产生的松散固体物质,是泥石流活动的物质基础;沟道受松散岩土体堵塞,有利于泥石流规模放大;"快速激发型"的雨量特征为泥石流暴发提供了动力。在此基础上讨论了泥石流起动、运动和堆积过程,总结了泥石流活动特征,发现泥石流沿发震断裂呈"带状"分布,成因组合上属于"降雨控制型",尚处于"青年期",且在成灾模式上满足"致承耦合"效应。

汶川地震灾区生物多样性热点地区分析

汶川地震灾区位于长江上游,是我国大熊猫(Ailuropoda melanoleuca)的主要分布区,被保护国际认定的25个全球生物多样性热点地区之一。2008年5月12日发生的汶川大地震导致该区域生态环境遭受严重破坏,需要识别生物多样性热点地区,指导灾后生物多样性保护。选取物种生境质量、植被景观多样性指数和物种多样性指数作为评价指标,其中生境质量采用InVEST生物多样性模型计算,然后利用空间相关分析中G系数进行热点地区分析,探测出灾区生物多样性的热点区,并在此基础上与现有保护区分布、物种生境分布以及Marxan模型计算出的优先区进行对比验证。结果显示:热点区范围涉及到现有76%的保护区,且保护区内的热点区面积达到灾区所有保护区面积的55%;在选取的69个指示物种中有60个物种位于热点区的生境面积占这些物种在灾区的总生境面积的50%以上,有32个物种在80%左右,热点区内的所有指示物种生境总面积占整个灾区指示物种生境总面积的70%以上。基于空间相关分析方法得出的热点地区基本上与Marxan模型输出的优先保护区范围结果基本一致。但空间相关分析的热点区划分克服了Marxan模型优先保护区分布过于离散,孤岛效应明显的不足。

龙门山小鱼洞断裂在汶川地震中的地表破裂及地质意义

在龙门山中段小鱼洞地区映秀-北川断裂和彭县-灌县断裂发生了同震位移,同时在该地区新出现了一条北西向的同震破裂带——小鱼洞断裂的破裂带,并分割了两条近于平行的北东向逆冲-走滑型的主断裂。汶川特大地震发生后重点对小鱼洞断裂的地表破裂开展了详细的野外地质填图,利用全站仪和GPS对地表破裂进行了精确的测量。初步调查的结果表明,小鱼洞断裂位于映秀-北川断裂与彭县-灌县断裂之间,走向近于北西向,延伸约15km,以脆性破裂为特征,穿过小鱼洞大桥,并切割了多种类型的地貌单元,使道路发生拱曲、破坏和桥梁垮塌或移位。单个破裂长度在几米到300m不等,其南西盘为上升盘,北东盘为下降盘,平均垂直位错为1.0m,平均水平位错为2.3m,垂直与水平位错量之比1:1～1:2,显示为逆冲分量小于或等于左旋走滑分量,并以左旋走滑作用为主。同时,研究表明小鱼洞断裂属于映秀-北川断裂与彭县-灌县断裂之间的捩断层,其主要特征包括:1)是在汶川地震中由于龙门山逆冲体之间的差异逆冲运动过程中而形成的断裂;2)其走向近于北西向,垂直于龙门山北东向的主干断裂,而平行于逆冲体的逆冲运动方向;3)具有高角度断面的断层,以左旋走滑作用为主。

2008年汶川地震重灾区的泥石流

2008年,在"5.12"汶川地震后,随着降雨的发生,地震重灾区的中高山区较普遍地多次发生了泥石流灾害,尤其是对一些地震灾民安置点板房区造成了危害,累计造成人员伤亡(含失踪)达450余人,进一步加重了灾情。按照地震与泥石流暴发的时间顺序分类,区内的泥石流属后发型地震泥石流。其特征主要为:泥石流活动频率增高,暴发点多,规模大小不一,流体性质一般以粘性为主,密度值多在2.0～2.3 t/m3之间;泥石流的活动范围与降雨关系密切,活动范围还受地形因素控制,主要集中在龙门山等中高山区;泥石流危害形式有冲毁、淤埋、堵塞主河等多种形式。因此,在汶川地震重灾区这样的区域选址恢复重建,实质上是在工程地质条件复杂的不稳定区内选择相对稳定的安全岛,可供选择的场地极为有限。故恢复重建居民点时应因地制宜,尤其是岷江等江河峡谷区等地的居民点重建,宜保持当地居民传统的分散、多点居住的特点,而不宜于搞成规模较大的集中成片的居民点。这样既有助于场址的安全,又可以避免大规模泥石流、滑坡、崩塌、山洪等山地灾害发生时造成大量的人员伤亡。地震重灾区2008年的泥石流活动显示,龙门山及邻近的邛崃山等山区因汶川地震的影响,泥石流已进入强烈活动时期。其强烈活动时间,可能持续10～30 a,甚至更长。对此,要有足够的重视。在可能遭遇泥石流的区域开展的各种工程建设,一定要加强防范措施,防止泥石流危害。

地震前后灾区旅游地国内游客旅游动机变化研究——以“5.12”汶川地震前后的九寨沟为例

认清灾害事件对游客动机的影响是灾后旅游市场恢复第一步。根据"5.12"汶川地震发生前(2008年4月27～5月5日)与发生后(2009年5月5～10日)两个时段游客问卷调查数据,采用多因素方差分析等方法定量研究地震对灾区旅游地国内游客旅游动机的影响。研究发现,地震对游客大部分动机影响显著,震后拉力动机重要性下降,推力动机除遗产名气大动机外其余都增强,震后休闲动机比求知动机重要,与震前截然相反。震后旅游地非核心旅游吸引物的吸引力变化幅度呈现距离递增趋势,但核心旅游吸引物吸引力变化不存在空间差异。地震前后游客到访世界自然遗产地最重要的动机都是"亲近了解自然",与旅游吸引力不突显吸引物所激发的动机一样,不受地震灾害的影响。