Analysis of the 1976 Tangshan earthquake process
SONG HUIZHEN ‘, YUAN YANGUANG ’ and HUANG LIREN *
nstitute of Geology, State Seismological Bureau, Beijing (China) 2Geodetic Brigade, State Seismological Bureau, Tianjin (China)
(Received by publisher May 9, 1989)
Institute of Geology, State Seismological Bureau, Beijing (China) 2Geodetic Brigade, State Seismological Bureau, Tianjin (China)
(Received by publisher May 9, 1989)
Song Huizhen, Yuan Yanguang and Huang Liren, 1990. Analysis of the 1976 Tangshan earthquake process. In: S. Das and M. Ohm&a (Editors), Earthquake Source Processes. Tectonophysics, 175: 119-130.
A discrete crack model of the strain accumulation of the Tangshan rhombic block, together with slip and stable extension of the earthquake fault prior to and during the 1976 Tangshan earthquake, is presented. It includes two processes: frictional slip along the crack and stable extension of the crack tips. The finite element technique is used to calculate stress and deformation along the crack surface and stress intensity factors at the crack tips, and the Mom-Coulomb principle is applied to judge the existence of frictional slip along the crack surfaces and to determine the crack extension direction using the maximum circumferential tensile stress criterion. The similarity between the data predicted by the model and the data collected during the field survey indicates that the crack model has successfully simulated the process of strain accumulation and fracture propagation prior to and during the Tangshan earthquake.
The numerical model on the 1976 Tangshan earthquake is based on the concept of frictional contact of discontinuous solid surfaces and on the theories of stable extension of the crack, with the geodetic survey data and the focal mechanism solutions as the constraint conditions for simula- tion.
Concept of the crack model
Triangulation data indicate:
Tangshan rhombic block was in a locked state prior to the Tangshan main shock, (2) the defor- mation of the Tangshan earthquake fault was very large during the main shock, but the adjustment in deformation after the earthquake was small, and (3) that consequently the Tangshan earthquake was due to sudden slip of the two walls of the
Tangshan fault. Therefore, the rhombic block it- self and its surrounding blocks may be treated as a contact system consisting of multiple deformable solid bodies, and the fault can be taken as two contact surfaces. We distributed a series of nodal pairs along the surface to form a set of contact elements. Special triangular elements with quarter-point nodes are used to deal with the stress singularity at the crack tip (Fig. 1). The stiffness equations are first separately formed for the different contact bodies and then linked up into the total stiffness equation, according to the boundary conditions for different contact states.
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