THREE DIMENSIONAL ANALYSIS OF FRACTURE PROCESS OF THE 1976 TANGSHAN EARTHQUAKE
ZHANG ZHILI (Institute of Geophysics, State Seismological Bureau)
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.