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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。
The 2008 Wenchuan earthquake (M_s8.0) has formed the most complex and lengthy thrust-type coseismic surface rupture zone so far. The determination of the coseismic slip along the length of about 275 km and the maximum slippage of the surface rupture zone is of great significance for understanding and understanding the surface rupture process and the deformation mechanism of the Wenchuan earthquake. We conducted a detailed study of slip features along the surface rupture zone and measurements of its coseismic displacements. We found that the two slippage peaks are distributed along the Ying-Ying-Beichuan fault zone, and the southern segment is centered on the Shenxigou-Hongkou rupture zone. The thrust is mainly accompanied by the right-lateral strike-slip movement, the maximum vertical displacement is 6.0 ~ 6.7m, the north segment is centered on the Beichuan fault, and the dextral strike-slip is mainly accompanied by the thrust movement. The maximum vertical displacement For 11 ~ 12m, the two surface rupture events represented by the two north-south peak-slip sections are consistent with the seismic data inversion results. Through the fine terrain profile measurement of the Beichuan section rupture zone and comparison before and after the earthquake, the maximum right-handed horizontal displacement of this rupture section obtained in a group of Shaba Village, Quanshan Town, Beichuan County is 12 ~ 15m and the maximum vertical displacement is 11 ~ 12m. This is the largest coseismic vertical displacement produced by an earthquake in the world at present. The maximum slipping slip is 14-17 m, which is the maximum surface rupture slip of the entire Wenchuan earthquake and is the macro epicenter of the Wenchuan earthquake. High-angle seismic rupture at Beichuan rupture, reversal of thrust rupture, and strong deformation with maximum slip are the main causes of Beichuan’s strongest surface damage and geological disasters. The oblique thrusting with near-consistent strike-slip and thrust reversal (horizontal displacement of strike slip / vertical displacement of thrust of 1) may be an important mechanism for rapid uplifting of the mountains.