汶川MS8.0级地震断层滑动机制研究

汶川M_S8.0级地震的发震构造为龙门山断裂带，地震地表破裂主要分布在其中的北川－映秀断裂和江油－灌县断裂上，尤其是沿前者发育了长达240 km左右的地表破裂带.通过对龙门山断裂带震后断层擦痕的测量，得到311条断层擦痕数据，利用由断层滑动资料反演构造应力张量的计算方法，得到研究区8个测点的构造应力张量数据，并获得了研究区构造应力场特征：区域现代构造应力场以近水平挤压为主，最大主应力方向（σ1）为76°～121°，平均倾角9°，应力结构以逆断型为主.受构造应力场及断层几何特征的影响，地表破裂呈现出分段性：映秀—北川段主要以NW盘逆冲为主，垂直位移明显；北川以北段为逆冲兼走滑，水平位移量与垂直位移量基本相当，或水平位移略大.

The mechanics of fault slip of MS8.0 Wenchuan earthquake

The seismogenic structure of the M_S8.0 Wenchuan earthquake is the Longmenshan fault zone. Its surface rupture occurs mainly on the Beichuan-Yingxiu fault and the Jiangyou-Guanxian fault, especially the former, with a length of 240 km. By field investigation and observation, we got 311 data of active fault slickensides. And using the method of inversion of fault slip data, we can obtain the parameters of 8 tectonic stress tensors and the characteristics of recent tectonic stress field in the Wenchuan region. The result shows that the recent tectonic stress field in the region is characterized by horizontal components. The maximum compressional stress is nearly in EW direction, and the stress regime is of reverse-fault type. The direction of the maximum principal compressional stress (σ1) is 76°～121°, and the average dip angle is 9°. Spatial distribution of the tectonic stress field and the geometrical characteristics of the Longmenshan fault zone show that the surface rupture has segmented characteristics. Up-thrust of the northwest wall is the main vertical slip on the Yingxiu-Beichuan segment. Both reverse faulting and strike slip occurred on the segment to the north of Beichuan, and strike slip offsets are greater than the vertical ones in some places.