Improvements to EXSIM in Ground Motion Simulation for Earthquakes Explained by Double-Corner-Frequency Source Model

The stochastic EXtended finite-fault ground-motion SIMulation algorithm (EXSIM) has been widely applied in simulating and predicting broadband strong ground-motion. However, an increasingly number of researchers have found that EXSIM may overestimate ground-motions at low frequencies for some large-magnitude earthquakes and/or thrust earthquakes, for which the far-field source model has been explained by a double-corner-frequency model. Despite controversy, the double-corner-frequency model is now being accepted as one of the main categories of the far-field source model. This study demonstrated the limited applicability of EXSIM to earthquakes explained by the double-corner-frequency source model, by presenting the equivalence between motions generated by EXSIM and those generated by EXSIM's point-source version, SMSIM, which adopts the ω-square single-corner-frequency model. Furthermore, two improvements to EXSIM have been proposed: (a) the incorporation of the asperity-distributed stress-drop compound faults model and (b) the hybrid application of EXSIM with the proposed model. The effects of the two improvements have been verified by comparing EXSIM-generating motions with recorded ground-motions for the 2013 M_w 6.7 Lushan thrust earthquake. Significantly, consistent simulation accuracy has been achieved across high- and low-frequency bands as well as in far- and near-fields. The consistent accuracy of the improved EXSIM in simulating high- and low-frequency ground motions enables its direct and independent application to broadband ground motion simulations. Moreover, the first validation of this consistent accuracy in both near- and far-field scenarios further enhances its application in earthquake engineering practices.