唐山地震破裂过程的三维分析

THREE DIMENSIONAL ANALYSIS OF FRACTURE PROCESS OF THE 1976 TANGSHAN EARTHQUAKE

本文提出一个三维力学模型,对1976年7月28日唐山地震的破裂过程做了进一步的理论分析。结果表明断裂面长轴两端存在一个10°左右的α角域,在这个角域内断裂面前缘的初始扩展方向是非共面扩展,即在与断裂面本身偏离一个角度(φ_0,θ_0)的面内扩展,而在其它区域断裂面的前缘是沿自身平面扩展的。在邻近长轴端部的点,扩展角φ_(?),0o=80.5°,这和二维分析得到的扩展分支的方向一致。由于主断裂面在长轴端部10°角域左右的非共面扩展,大量余震沿此方向发生,断裂面变成扭曲形状。

Following a previous paper by the same author, the fracture process of the Tangshan Earthquake of July 28, 1976 is hereby further studied. A three dimensional mechanical model is now presented and more complete results in comparison with that by two dimensional model are obtained. It is found that there exists an alpha (α) angulad region of about 10?near each end of the major axis of the main fault. Within the angular region, the initial extension direction of points on the fault front is no longer coplanar with the plane of the main fault but in a plane making an angle (φ0,θ0) with it. However for other parts of the fault, the front extents in the fault plane. Near the end points of the major axis the angle φ0≈0 θ0≈80.5 °They agree with the didections obtained from two dimensional analysis. It is because that the extension within the angular region of about 10?at the end points of the major axis of the fault plane is not coplanar, a large number of aftershocks occurred along this direction. So the fault plane becomes contorted in shape.