DISTRIBUTION,CHARACTERISTICS,AND ASSOCIATED INFLUENCIAL FACTORS OF THE GEOHAZARDS INDUCED BY MINXIAN-ZHANGXIAN EARTHQUAKE ON 22 JULY,2013,GANSU,CHINA

On July 22,2013a catastrophic earthquake with M S6. 6 occurred at the conjunction of Min and Zhang Counties,Dingxi City,Gansu Province,China. The seismic activities have caused a wide spread of damages to houses and infrastructures,and induced a series of potential hazards such as landslides,collapses and unstable slopes. This paper summarizes the types,distribution and major characteristics of the potential geohazards induced by the earthquake. Two indices including number of the slope geohazards and area development rate are used to analyse the relationship between the potential geohazards initiated by the earthquake and other controlling factors such as topographical,geological and seismic conditions in the epicenter area of Min County. The results show that:( 1) The potential geohazards initiated by the earthquake are distributed in the area where elevations are in the range of 2200m to 2800m,slope gradient in 0° ～ 15°,slope aspects in S,SW and W,and topographically at the middle parts of slopes;( 2) The soft rocks are prone to landslide under seismic vibrations. The Devonian and Permian slate and limestone group produces about 50% of the geohazards in the whole earthquake affected area.The thick Neogene soft mudstone and sandstone group hosts the highest geohazards development rate. The main geohazards concentrate along or within 20km distance to the earthquake causative fault;( 3) The correlation between individual geohazard scales and their distances to the epicenter and PGA are not significant. However,the general trend is obvious,as the development rate decreases with the increasing distance to the epicenter and increases with the increasing PGA. The greater the seismic intensity,the higher the probability of geohazards occurrence;( 4) The closer to roads and river,the higher of the development rate of the geohazards,especially within the distance of 0 ～800m to the roads and 0 ～ 600m to the streams or rivers.