Finite fault source model and analysis for ground motion near-fault zone
For ground motion in near-fault zones includes,the impulsive component usually causes larger damage than that in far-fault ground motion,which results in bridge collapse.In order to assess the near-site seismic effect of the fault site and provide data for Benchmark modeling platform of cable-stayed bridges across faults,a numerical model using finite faults based on the geological and structural characteristics of the old earthquake site in Qiongshan was proposed with an orthotropic simulation,which includes fault impact zones construction,the determination of average slip on fault rupture surfaces and point-source ground vibration simulations.The observation points were obtained,and the analysis results with the impulsive characteristic parameters of the recorded ground of the similar grade were compared with the proposed model.And the ground shaking in the near-fault region was analyzed to verify the finite fault seismic model.The results show that the smaller the apparent dip angle of fault rupture plane has,the larger maximum peak ground acceleration PGA、ratio of peak velocity to ground acceleration PGV2A and Arias strength Ia are induced,and the stronger the ground motion pulse is generated.The value of peak ground acceleration in the direction of the vertical fault rupture surface PGAv and PGV2A on the hanging wall or along the direction of propagation is larger than those on the footwall,which displays the hanging wall effect and directional effect of near-fault earthquakes,while the distribution law of peak ground acceleration in the direction of a parallel fault rupture surface PGAp,Ia and ratio of Arias strength in the two horizontal directions Iy2x is on the contrary,which is due to that the lateral ground motion is closer to the faults at the observation points of lower disk.PGA is close to CHY101(Mw7.62 oblique slip fault)in 1999 ChiChi Earthquake.In addition,the characteristic parameters of other ground motion pulse in the simulated ground motion of Mw7.5 normal fault have good agreement with 1980 Irpinia Sturno(Mw6.9 normal fault).3 tabs,9 figs,24 refs.