Broadband Ground Motion Simulation Method Considering Nonlinear Site Effects

Numerical simulation is one of the most important tool in the research on earthquake ground motions,especially in seismic hazard assessment for areas lack existing recordings.However,several aspects still need further consideration,including broadband simulation and site effects analysis.On the one hand,broadband response of 0.1?20Hz are all vital information for seismic design,but there are difficulties in applying small-scale source and model data as inputs for simulation in high-frequency band.Hybrid methods,which combine low-frequency deterministic methods and various high-frequency methods,are widely used to make up for this defect and give broadband simulation results.On the other hand,the influence of site effects on strong ground motion is of a great concern in many areas.But due to low-velocity and non-linearity,the non-linear site effect is usually not included in the physics-based numerical simulations(PBSs),instead is generally implemented by a post-correction approach.Since the correction process is often completed via closed-source commercial softwares,which may introduce some restrictions in use,it's an effective improvement to incorporate site-analysis module based on broad-band ground motion simulation,and generate a complete modeling system for seismic hazard assessment in China.We developed a new program in this study,to extend the Collocated Grid Finite Difference Method(CG-FDM)into combined broadband ground motion simulation considering nonlinear site effects,by coupling finite-fault high-frequency stochastic simulation method and 1D frquency-domain equivalent-linear site effect analysis method.In the program,kinematic seismic source-rupture model,regional velocity-structure model,and nonlinear soil properties to depict backbone and hysteretic curves for layered models at discrete grid-points are needed as inputs,and thus the time history and frequency spectra are given as results for broadband synthetic seismic response considering site-effects.Furthermore,the high-frequency stochastic method is modified in this study to include finite-fault models and arrival time modifications,and the high-frequency and site-analysis modules are tested and analyzed seperately,after which the whole modeling system is guaranteed to be capable in regional strong ground motion simulation given large-fault earthquakes,complex media and topography.We apply above methodology and program on strong ground motion simulation ofthe 2008 Mw7.9 Wenchuan earthquake within Sichuan area,where the necessary source,medium,and soil data of the surrounding region have been obtained by previous researchers.The synthetic seismic response fits the observed seismic recordings better than deterministic methods only.Since all three computation modules needed in simulation are combined organically,it could achieve all objectives in strong ground motion simulation at one run,and is expected to be used more widely in seismic hazard analysis and earthquake engineering.