Equivalent Mechanism of EXSIM and SMSIM Under Fixed <i>R</i><i><sub>JB</sub></i>

In this study, under a fixed <i>R</i><i><sub>JB</sub></i> distance given by the EXSIM model, we systematically analyze the correspondence between the finite-fault model (EXSIM) and the equivalent point-source model (SMSIM) in ground motion simulations. Based on regional parameters from California, simulations are conducted for four moment magnitudes ranging from <i>M</i><i><sub>w</sub></i> 6.0 to 7.5. Through the equivalent distance model and the method of minimizing spectral residuals, the SMSIM parameters that achieve the best match in response spectra between the two types of models are determined. The results show that under the same set Joyner–Boore distance (<i>R</i><i><sub>JB</sub></i>), the equivalent <i>R</i><i><sub>JB</sub></i> value corresponding to the SMSIM simulation that best matches the EXSIM results is not necessarily equal to the <i>R</i><i><sub>JB</sub></i> value set in EXSIM, especially in the near field where a systematic shift is observed. More importantly, in the near-field region, to match the finite-fault effects of EXSIM using SMSIM, the equivalent depth <i>h</i> obtained is significantly greater than the actual set source depth. This phenomenon indicates that within the point-source framework, to equivalently represent near-field saturation effects and the influence of finite fault spatial extension, an “equivalent depth” larger than the true physical depth must be introduced as compensation. This study quantitatively reveals two key patterns: “equivalent <i>R</i><i><sub>JB</sub></i> shift” and “equivalent <i>h</i> enhancement,” establishing a parametric matching relationship from the far field to the near field. It provides important conversion criteria and physical insights for the engineering-equivalent application of finite-fault and point-source models in ground motion simulation.