2008年汶川地震导致的斜坡物质响应率及其空间分布规律分析

RESPONSE RATE OF SEISMIC SLOPE MASS MOVEMENTS RELATED TO 2008 WENCHUAN EARTHQUAKE AND ITS SPATIAL DISTRIBUTION ANALYSIS

提出地震斜坡物质响应率(Response Rate of Seismic Slope Mass Movements,RRSSMM)的概念,然后基于汶川地震滑坡详细编录图,结合汶川地震导致的斜坡物质运动形式(滑坡)的"面积–体积"经验公式,对汶川地震导致的斜坡物质响应率及其空间分布规律开展研究,基于1 km2的正方形网格构建整个震区的地震斜坡物质响应率分布栅格图与等值线图,统计斜坡物质响应率大小与分布面积的关系,揭示地震斜坡物质响应率与分布面积之间的幂律关系。大光包滑坡(汶川地震触发的规模最大的滑坡)处的RRSSMM最大,达到47.923 5 m。RRSSMM超过1 m的区域主要分布在映秀—北川地表破裂南西段(映秀镇与北川县之间)对应的上盘区域,这一区域恰对应着逆冲分量为主的断裂上盘,这表明逆冲断裂对上盘区域发生滑坡的极强烈的控制作用。基于GIS技术与统计学理论,开展不同地震滑坡影响因子控制下的斜坡物质响应率空间分布规律分析,这些因子包括地形因子、地质因子与地震因子,分别为高程、坡度、坡向、斜坡曲率、斜坡坡位、与水系距离、岩性、与震中距离、与北川—映秀断裂距离、沿着北川—映秀断裂距离、地震动峰值加速度(PGA)与地震烈度。分析结果表明,RRSSMM随着坡度、地震烈度、PGA的增加而增加;随着与震中距离、与北川—映秀断裂距离、与水系距离的增加而减少;最大的RRSSMM值高程范围为1 600~1 800 m;最大RRSSMM值对应坡向为E方向;曲率越接近0,RRSSMM越小;坡位为中坡、下坡与谷底的RRSSMM值最高;砂岩、粉砂岩(Z),砂岩、粉砂岩、硅质岩、板岩(∈)这两类岩组是RRSSMM的高值岩性组合;沿着北川—映秀断裂的RRSSMM统计结果表明,逆冲运动习性的断裂比走滑习性的断裂对斜坡物质响应率具有更强烈的控制作用。该研究成果可为汶川地震区的河流与地貌演化、滑坡与泥石流研究等提供基础数据,也可指导其它地震触发的区域群体性滑坡事件的同类研究。

As the main phenomenon of slope mass movement response on earthquake,research of earthquake triggered landslides has important practical applications and theoretical scientific significances,especially related to the 2008 Ms 8.0 Wenchuan Earthquake. Landslides caused by the earthquake are widespread concerned due to they caused strong landscape changed,enormous loss of life and property damages. In present research,the concept of response rate of seismic slope mass movement(RRSSMM) was proposed. In the first stage,a landslide inventory map was prepared using the landslides triggered by the Wenchuan Earthquake,and was delineated from interpretation of aerial photographs,and field surveys. In the second stage,distribution raster and isoline map of RRSSMM are constructed based on“area-volume”correlation of landslides per 1 km2 grid cells. Next,Area distribution map of RRSSMM was constructed , and it showed that relationship of frequency-RRSSMM or area-RRSSMM in coincidence with power law in range of RRSSMM less than or equal to 10 m. It is showed that the maximum RRSSMM value appears at the position of Daguangbao landslide (the largest landslide triggered by the Wenchuan Earthquake),up to 47.923 5 m. Areas of RRSSMM value exceeding 1 m almost appear in the northwest facing areas,on the hanging wall,of a section of Yingxiu-Beichuan fault (from Yingxiu Town to Beichuan County). Those areas of high RRSSMM values correspond to hanging wall of thrust fault. It is indicated that strong controlling of earthquake on landslide occurrences on hanging wall of thrust fault. Spatial distribution analysis of RRSSMM controlled by different landslide conditioning factors were carried out base on GIS technology and statistical theory. These landslide conditioning factors include topographic factors,geologic factors and seismic factors,such as,elevation,slope angle,slope aspect,slope curvature,slope position,distance from drainages,lithology,distance from the epicenter,distance from the Yingxiu-Beichuan fault,distance along the Yingxiu-Beichuan fault,peak ground acceleration(PGA),and seismic intensity. The statistical results show that RRSSMM has positive correlation with slope angle,PGA,and seismic intensity,and negative correlation with distance from drainages,distance from the epicenter,and distance from the Yingxiu-Beichuan surface fault-rupture. It also represents the maximum value of RRSSMM appears between 1 600-1 800 m ranges in elevation. The highest RRSSMM value has preferred orientation,dominated by the eastern facing. There were small RRSSMM close to zero for plan curvature. For slope position,middle slope,lower slope and valley occupy the highest RRSSMM values. The two lithology groups of sandstone,siltstone (Z) and sandstone,siltstone,chert,slate (∈) had the highest RRSSMM values. The statistical results of RRSSMM along the Yingxiu-Beichuan fault show that the RRSSMM strongly affected by fault in thrusting movement feature. The final RRSSMM distribution data is of great significance on rivers and geomorphic evolution,and debris flow researches,and it can be timely shared to researchers in related fields,such as,tectonic geomorphology,engineering geology,environmental geology, and geological hazards etc. Research methods in this research can be applied to other regional seismic landslide events.