近地表倾角和无地表破裂前期逆冲地震对汶川MS8.0地震逆冲滑动量随深度分布形态的影响

逆冲滑动是汶川地震的初始和主要震源过程，其破裂滑动量随断层深度的分布形态与多数板内逆冲强震不一致.本文用摩压比值来表征断层沿线的局部破裂危险程度，通过数值实验讨论了底部破裂源、近地表倾角和无地表破裂的前期地震等对铲形逆冲断层的破裂危险分布和破裂滑动分布的影响.有限元数值模拟结果显示，在巴颜喀拉块体对龙门山断裂带的高强度挤压下，上陡下缓近地表陡倾角的铲形断层形态使得汶川发震断层近地表对逆冲破裂和滑动有一定的阻碍作用；破裂滑动量集中于发震断层中部的前期逆冲地震是造成汶川M_S8.0地震逆冲滑动分布异于板内逆冲强震滑动分布现象的一个可行解释.

Influences of the near-surface dipping angle of the fault and previous thrust earthquakes on slip distribution with depth of the 2008 Wenchuan MS8.0 earthquake

Thrust rupture is the initial and main course of the 2008 Wenchuan M_S8.0 earthquake. Its distribution on the causative fault plane with depth is inconsistent with most thrust earthquakes of plate interiors. Through numerical experiments, this work analyzes the influences of the source at the bottom, near-surface fault dipping angles and previous earthquakes on such distribution. The results show that under the intense compression from the Bayan Hara block in the northwest, the listric near-surface fault surface hampers the rupture and slip of the Wenchuan event to some extent. That the ruptures of previous thrust quakes are concentrated in the middle portion of the fault is one of the possible reasons for that the slip distribution of the 2008 Wenchuan event is different from most intraplate quakes of thrust type.