Three-dimensional modeling of near-field ground motion with relation to fault geometry and driving force

Abstract The initial baseline stress is first calculated quasi-statically under various loading conditions by using a three-dimensional finite-element 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 recalculated by reducing the shear resistance of the faulted plane with the same boundary conditions. Then the difference between the baseline stress before faulting and the new stress state during faulting is regarded as the driving force to estimate the near-field ground motion. Numerical results show that both the fault geometry and the loading system play an important role in the distribution of the intensity of the ground motion. For instance, a reactivated pre-existing fault in a sedimentary 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 horizontal driving force to avoid thrust faulting as is evident from the 1976 Tangshan earthquake.