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Abstract:
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为深入理解汶川地震破裂的构造运动机制，本文选取典型的观测点，利用多种地质地貌标志测绘分析得到了汶川MS8.0地震发震断裂的近地表三维同震滑移矢量.结果显示，北川—映秀断裂上的白水河—高川破裂段北西盘沿88°方位角水平滑移2.58 m、垂直滑移3.70 m；安县—灌县断裂上的白鹿—汉旺破裂北西盘沿134°方位角水平滑移1.63 m，垂直滑移2.00 m；小鱼洞破裂带南西盘沿76°~79°方位角水平滑移2.15~2.71 m，垂直滑移1.36~1.51 m.平行的白水河—高川破裂段和白鹿—汉旺破裂段合计形成1.72 m右旋走滑和3.49 m垂直断裂带的NW向水平缩短，总滑移方向（106°）与断裂带整体走向（42°）呈64°夹角，整个龙门山推覆构造带处于斜向挤压的构造环境.结合震源过程反演成果的分析显示，斜滑的白水河—高川破裂段和逆冲型白鹿—汉旺破裂段可能是在汶川地震中最大的一次子事件过程以滑移分解的形式而同时破裂形成的，滑移分解作用使两条断裂以斜滑与逆冲组合的力学性质产生破裂而非相同性质的斜滑破裂.小鱼洞破裂以低角度斜滑为主，可能是安县—灌县断裂与北川—映秀断裂以滑移分解形式同时破裂的纽带.小鱼洞断裂是龙门山断裂带长期处于斜向挤压的构造环境的产物，不只是逆冲断裂系中的捩断层.
In order to study the kinematical mechanism of the co-seismic rupture of the 2008 Wenchuan earthquake, we implemented a detailed surveying and mapping in some typical sites with geological and geomorphologic marks, and calculated the three dimension slip vectors. The northwestern hanging wall of Baishuihe-Gaochuan rupture associated with the Beichuan-Yingxiu fault slipped in an azimuth of 88°, with 2.58 m of horizontal slip and 3.70 m of vertical slip; The northwestern hanging wall of Bailu-Hanwang rupture associated with the Anxian-Guanxian fault slipped in an azimuth of 134°, with 1.63 m of horizontal slip and 2.00 m of vertical slip; The southwestern hanging wall of Xiaoyudong rupture slipped with an azimuth of 76°~79°, 2.15~2.71 m of horizontal slip and 1.36~1.51 m of vertical slip. There are totally about 1.72 m of strike slip and 3.49m of horizontal shortening perpendicular to the fault zone from the paralleling Baishuihe-Gaochuan and Bailu-hanwang ruptures. The integrated slip vector (trending 106°) has an angle of 64° with the fault zone (trending 42°) , and the Longmenshan fault zone was under a transpression. Combining the result from source inversions, we propose that the oblique-slipping Baishuihe-Gaochuan rupture and the dip-slipping Bailu-Hanwang rupture were produced in the same time during the largest sub-event with a slip partitioning, and the mechanism of slip partitioning made the two faults ruptured with an oblique slip and a dip slip, but not all the same oblique slip. The Xiaoyudong rupture slipped in a relatively small dip angle, which acted as a trigger structure for the simultaneous rupture of Beichuan-Yingxiu fault and Anxian-Guanxian fault in a manner of slip partitioning. The Xiaoyudong fault was the production of the Longmenshan fault zone under the transpressional tectonics in a long term, not only a tear fault among the thrust system.
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