Asymmetric disaster distribution and its cause analysisof the MS8.0 Whenchuan earthquake

Seismic disasters displayed various asymmetrical distribution during the 2008 MS8.0 Whenchuan earthquake. The size and quantity of landslides and rock avalanches triggered by high－angle reverse faulting on the hanging wall are higher than on the footwall. In the direction perpendicular to fault strike, the zones with high intensity on the hanging wall are wider than on the footwall. These asymmetries reflect hanging wall effect on peak ground acceleration in reverse faulting event. In the direction of rupture propagation, Doppler effect induced intensity attenuating slowly northeastward and rapidly southwestward. In the region between mountain and basin, heavy casualties and serious destruction of buildings are probably caused by site magnification and basin effect. Possible reason for the buildings near surface rupture zone having withstood the strong earthquake is that the effective stress drop and rupture velocity generation surface fractures may be low there, resulting in a relatively low ground motion around the period of 1 sec. The near-surface seismogenic fault being steep is another reason for the fact that the surface intense deformation zone is narrow.