3-DIMENSIONAL MODELING OF NEAR-FIELD GROUND MOTION WITH RELATION TO FAULT GEOMETRY AND DRIVING-FORCE

The initial baseline stress is first calculated quasi-statically under various loading conditions by using a three-dimensional finite-elemen t scheme with double nodes to simulate stress on a locked fault. Once the shear stress at the end of the fault reaches the rupture criterion , the accumulated stress is suddenly released simultaneously causing a frictional slip along the fault plane. The new state of stress is rec alculated by reducing the shear resistance of the faulted plane with t he same boundary conditions. Then the difference between the baseline stress before faulting and the new stress state during faulting is reg arded as the driving force to estimate the near-field ground motion. N umerical results show that both the fault geometry and the loading sys tem play an important role in the distribution of the intensity of the ground motion. For instance, a reactivated pre-existing fault in a se dimentary basin would cause greater damage and more subsidence on one side of the fault than on the other side. For this to occur, a certain dip angle and the gravitational potential must overtake the horizonta l driving force to avoid thrust faulting as is evident from the 1976 T angshan earthquake.