The seismogenic tectonic mechanism of the Lushan M_S7.0 earthquake and the geomorphological response of the upstream drainage of Qingyijiang river,in 2013,Sichuan,China

On April 20,2013,in Sichuan Province,the Lushan MS7.0earthquake occurred on the southern segment of the Longmenshan fault belt.Through the analysis of the upstream geomorphology and the typical earthquake destruction characteristics,we probed into the seismogenic tectonic mechanism of the Lushan MS7.0earthquake in this paper.The analysis of the geomorphic features of the upstream drainages and hypsometric interval(HI value)of the drainage basins showed that the landscape development has obvious feedback effect on the neotectonic activities of the Longmenshan fault belt.The buildings,destroyed seriously in the earthquake,distributed as bands.The earthquake produced a large number of secondary surface tension cracks and a series of beaded liquefaction.The distribution of the surface destruction phenomenon was in parallel with the main faults and anticline.The aftershock distribution showed that the Lushan earthquake was closely related with the new activities of the Shuangshi-Dachuan fault,Xinkaidian fault and Dayi fault.The Longmenshan fault zone is a typical thrust-nappe structure.And the seismogenic structure of the Lushan earthquake has the same characteristics.Upstreams of the Qingyijiang river cross the southern segment of the Longmenshan fault belt.Combining the geomorphological response process of the southern segment of the Longmenshan,the characteristics of the surface damages of the Lushan earthquake and the aftershock distribution,the Lushan earthquake was ascribed to the result of the ceaselessly propagating of the Longmenshan thrust fault belt in SE direction and the compression and shortening of the crust.