STRUCTURAL PROPERTY OF THE CRUST AND THE UPPER MANTLE IN THE TANGSHAN EARTHQUAKE REGIONA METHOD OF COMPUTING BODY WAVE THEORETICAL SEISMOGRAM AND THE RESULT OF ANALYSIS OF 2-D INHOMOGENEOUS MEDIA

In order to study the propagation of waves in 2-Dlaterally inhomogeneous isotropic and absolute elastic media with curved interfaces, it is appropriate to calculate the wavefield using the solution of high frequency approximate expansion for elastic wave equation, under certain conditions.For the purpose of solving the system of twopoint ray tracing under certain initial conditions, the standard program (the method of Runge-Kutta) has been used. The geometrical spreading factor is determined by solving a system of two linear ordinary differential equations of the first order (the socalled dynamic ray tracing system) with a modified Eulers method. These are realized by the Seis 83 progam.In the present paper, the authors gave calculated with the Stis 83 program the observed data from two profiles (the Baigezhang-Fengnan-Fengning-Zhenglangqi profile and the Cang-zhou-Tianjin-Kelaqinzuyi profile) which pass through the epicentral region of the Tangshan earthquake where they intersect each other approximately perpendicularly. The structural property of the crust and the upper mantle in the Tangshan earthquake region and the relation between the Seismicity and the velocity distribution in the low-velocity layer of the crust are discussed.