【摘要】 2008年汶川地震(M_s8.0)形成了迄今为止空间上分布最为复杂、长度最大的逆冲型同震地表破裂带。沿约275km长的地表破裂带的同震滑移及其最大滑移量的确定,对认识和理解汶川地震地表破裂过程及其变形机制具有重要意义。我们沿地表破裂带进行了详细的滑移特征考察及其同震位移测量,发现沿映秀-北川破裂带分布南北两个滑移峰值区段,南段以深溪沟-虹口破裂段为中心,以逆冲为主伴随右旋走滑运动为特征,最大垂直位移量为6.0～6.7m,北段以北川破裂段为中心,以右旋走滑为主伴随逆冲运动为特征,最大垂直位移量为11～12m,南北两滑移峰值区段所代表的两次地表破裂事件与地震波数据反演结果一致。通过对北川段破裂带的精细地形剖面测量,以及地震前后对比,在北川县曲山镇沙坝村一组获得该破裂段的最大右旋水平位移为12～15m,最大垂直位移为11～12m,这是目前世界上一次地震产生的最大同震垂直位移,最大斜向滑移量为14～17m,为整个汶川地震地表破裂最大滑移量,是汶川地震的宏观震中。北川破裂段高角度的地震断裂、逆冲断裂面的倒转作用以及具最大滑移量的强烈变形作用是北川县城遭受到最强的地表破坏和地质灾害的主要原因。具有走滑量和逆冲量近一致(走滑水平位移/逆冲垂直位移比值为1)的斜向逆冲作用可能是山脉快速隆升的重要机制。更多还原

【Abstract】 The 2008 Wenchuan earthquake(M_S8.0)produced the world’s longest thrust-type co-seismic surface rupture zone,which has the most sophisticated spatial distribution.The determination of the co-seismic displacement and its maximum value along the 275km long surface rupture zone is important for understanding the rupture process and deformation mechanism of the event.According to our detailed field slip investigation and accurate co-seismic displacement measurements,two segments with slip peak value are determined along the Yingxiu-Beichuan rupture zone:the south has the center of Shenxigou-Hongkou,is characterized by the thrust with dextral slip and the maximum vertical displacement is 6.0 ～6.7m; the north has the center of Beichuan,is characterized by the dextral slip with thrust and the maximum vertical displacement is 11 ～ 12m.The two rupture processes indicated by the two peak segments are agree with the seismic wave inversion(Chen et al.,2008; Ji,2008; Wang et al.,2008).By measuring the precise topographic profiles along the Beichuan segment,and comparing the features before and after the earthquake,at the site of unit one,Shaba Village,Qushan Town of Beichuan County,the maximum dextral displacement is 12～15m,and the maximum vertical displacement of 11 ～ 12m is the maximum value developed in one seismic event; the maximum oblique displacement of 14 ～ 17m is the maximum surface slip of the Wenchuan earthquake.This site is location of the macro-epicenter of the Wenchuan earthquake.The reasons why Beichuan County Seat underwent the most serious destruction and geological hazards include the high-angle seismic fault,the overturned thrust fault plane and the intense deformation with the maximum displacement.The oblique thrust with the similar horizontal strike-slip component and vertical thrust component ratio(Dh/Dv = 1)might be the key mechanism of mountains rapid uplift.更多还原