THREE-DIMENSIONAL NUMERICAL SIMULATION AND ANALYSIS OF SEISMOGENIC CONDITION AND TEMPORO-SPATIAL EVOLUTION OF PRECURSOR FIELD OF TANGSHAN M=7.8 GREAT EARTHQUAKE

At first, based on the observational data of deep seismic sounding, a 12-layered 3-dimensionai heterogeneous model of the upper lithosphere of North China was established, and the stress fields under the condition of an upwarp force effecting to basement and under the condition without such an upwarp force have been calculated by using the three-dimensional finite-element method. On the basis of the numerical simulation, the seismogenic condition and long-term precursor of Tangshan great earthquake were analyzed and researched. Sceondly, one layered 3-dimensional heterogeneous model of the lithosphere of Tangshan region and its vicinity which contains the surface and deep faults was considered. The non-symmetrical load condition was taken. The seismogenic body was simulated by hard inclusion, soft inclusion, and hard-soft inclusion of rectangular shape separately for the different stages of its evolution. The stress and displacement fields have been calculated by using the three -dimensional finite-element method, and based on the results of numerical simulation, the characteristics of temporo-spatial evolution of precursor field and the seismogenic process of Tangshan great earthquake were analyzed and discussed. The results obtained show that: (1) The focus of Tangshan great earthquake was located in a hard block of the crust of North China; (2) The upwarp force effecting to Crust basement from the Upple Mantle may play an important role in seismogenic process; (3) The characteristics of temporo-spatial evolution of precursor field of Tangshan great earthquake can be interpreted rationally by using the strong body earthquake-generating model.