Simulating the near-fault large velocity pulses of the Chi-Chi (Mw7.6) earthquake with kinematic model

The large number of pulses recorded during the 1999 Mw7.6 Chi-Chi Taiwan earthquake provided an important data for this study. The prediction of near-fault velocity pulses generated by large earthquakes can provide some reference for the Engineering anti-earthquake design. Based on the established source model and velocity structure model, this paper attempts to use the 3D finite difference method to simulate the 39 near-fault large velocity pulses. The conclusions are the following: (1) Two-segment “shovel-like” fault model constructed by 3D bending plane can better describe the characteristics of the underground real fault. (2) The seismic moment and rise time of the six asperities determine the peak and period of the velocity pulse. The asperities located at shallow low angle mainly affect the horizontal pulse components, and the asperities at high angle contribute more to the vertical pulse component. (3) The difference in sliding properties between the north and south ends of the fault causes a difference in the horizontal pulse components, reflecting the characteristics of the fling-step effect and directivity effect. (4) The characteristic period of the velocity response spectrum has the maximum near the turning point at the north end of the fault and shows a very obvious hanging wall effect in the near-fault region, resulting in the large-scale structures having severe damage because of large resonance effect. (5) Peak ground velocity (PGV) gradually increases from south to north along the fault and PGV on the hanging wall is significantly larger than PGV on the footwall, and the distribution of the pulses in front of the rupture is wider than that of the rear. Because the simulation results are basically consistent with the real records, this also verifies the feasibility of simulating pulse-like ground motions with the 3D finite difference method.