Site amplification and rupture velocity in EXSIM and updated EXSIM during the 2017 Mw6.6 Jiuzhaigou, China earthquake

The stochastic finite-fault technique based on dynamic corner frequency (EXSIM) is the most commonly used approach for obtaining near-field high-frequency ground motion and is regarded as an effective tool by researchers worldwide for simulating near-fault high-frequency ground motion. Because many model parameters in the finite-fault stochastic method are related to the source, site, and path, and the uncertainty of the input parameters frequently creates uncertainty of the synthesis results, it is difficult to obtain reasonable model parameters. The key point to consider when using EXSIM is how to determine the model parameters for ground motion simulation. Thus, the study investigated and discussed the sensitivity of some model parameters, such as site amplification and rupture velocity, to EXSIM synthesis results and updated modeling. The results showed that when the improved EXSIM was used, only the crustal site amplification function (CA) was adequate for Class A sites, whereas when EXSIM was used, both the CA and local site amplification (LA) functions had to be considered concurrently. Both CA and LA functions must be considered in the EXSIM for Class C and D sites. To obtain satisfactory synthesis results, the improved EXSIM requires only one LA function to be considered. Furthermore, the amplitude spectrum increased with rupture velocity, and the influence of rupture velocity was noticeable in the short period. These findings can serve as a foundation for highly reasonable and rapid model parameter determination, as well as improve simulation accuracy.