by Emrah Yenier
Department of Earth Sciences, University of Western Ontario
The characteristics of the apparent source spectrum of stochastic finite-fault simulations are evaluated to identify if the simulated ground motions exhibit “spectral-sag” at intermediate frequencies as a result of finite fault rupture. The finite-fault simulations are performed for various magnitude, stress-drop and distance bins. The Fourier acceleration spectra of the simulations are regressed for path effects in terms hypocentral and rupture distances to determine the apparent source spectra at the center and top edge of the fault, respectively. The source spectra obtained from simulations are compared with the Brune’s single-corner point-source model. The comparisons showed that the apparent source spectra of the finite-fault simulations match with the Brune model at all frequencies and they do not show “spectral-sag” that is observed in the empirical data from large earthquakes. It is also observed that the source spectrum of finite-fault simulations at the fault center is equivalent to the Brune model with a double stress-drop of finite-fault model. The discrepancy in stress-drops vanishes when the top edge of the fault is considered.
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