Asymmetric disaster distribution and its cause analysisof the MS8.0 Whenchuan earthquake
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摘要: 在汶川MS8.0地震中，地震灾害在灾区相对于发震断层，呈现各种非对称分布．断层高角度逆冲诱发的崩塌、滑坡的规模与数量在断层上盘区远远高于断层下盘区，在垂直断层方向，高烈度区断层上盘宽度往往大于下盘宽度，上述不对称性反映了逆断层型地震存在加速度峰值的上盘效应；而在破裂的传播方向存在的地震波多普勒效应则造成沿长轴方向东北部烈度衰减变慢、西南部烈度衰减变快；在山地与盆地过渡地带及盆地平原区，大范围的房屋受损、人员伤亡，则很可能为场地土层放大与盆地效应等所致；紧邻地表破裂带一些建筑物没有倒塌的事实表明，除建筑物的抗震性能存在差异外，还存在产生地表破裂的浅部有效应力降和破裂速率相对降低，导致1 s附近的地震动相对低下的可能性；而地表强变形带宽度较窄除破裂带处地震动相对较低外，地震断层倾角在地表变陡则是另一重要原因．Abstract: 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.
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