RESEARCH ON DEVELOPMENT AND DISTRIBUTION RULES OF GEOHAZARDS INDUCED BY WENCHUAN EARTHQUAKE ON 12TH MAY,2008

As Wenchuan earthquake was of high magnitude and shallow seismic focus,it caused considerable damage and thousands of geohazards. After a field investigation and the interpretation of remote-sensing images and aerial photographs taken after the earthquake,11 308 earthquake-induced geohazards have been obtained;and the general distribution situation of the geohazards has been learnt. Then,the distribution of these geohazards was investigated statistically using GIS techniques to determine how the occurrence of geohazards correlates with distance from the coseismic fault,slope steepness,elevation and rock type. The main results of this research can be summarized as follows. (1) The geohazards triggered by earthquake show the feature of zonal distribution along the coseismic fault and linear distribution along the rivers. (2) The distribution of earthquake-induced geohazards has marked hangingwall effect,for the geohazard concentration in the hangingwall of coseismic fault is obviously higher than that in the footwall and the width of strong development zone in the hangingwall is about 10 km. (3)the slope steepness is a main factor which controls the development of earthquake-induced geohazards and a vast majority of geohazards are distributed within the range of 20° to 50°. (4) The earthquake-induced geohazards have corresponding relationship with the elevation and micro-landform;for most hazards occur in river valley and canyon section below the elevation of 1 500 to 2 000 m,particularly in the upper segment of canyon section (namely,the turning point from the dale to the canyon). Thin ridge,isolated or full-face space mountains are most sensitive to the seismic wave,and have striking amplification effect. In these areas,collapses and landslides are most likely to occur. (5) The research also shows that different lithologies have no marked corresponding relationship with the development of geohazards,but it determines the types of geohazards. Usually,landslides occur in soft rocks,while collapses occur in hard rocks.