A Generalization of the Double-Corner-Frequency Source Spectral Model and Its Use in the SCEC BBP Validation Exercise

The stochastic method of simulating ground motions requires the speci- fication of the shape and scaling with magnitude of the source spectrum. The spectral models commonly used are either single-corner-frequency or double-corner- frequency models, but the latter have no flexibility to vary the high-frequency spectral levels for a specified seismic moment. Two generalized double-corner-frequency ω 2 source spectral models are introduced, one in which two spectra are multiplied to- gether and another where they are added. Both models have a low-frequency depend- ence controlled by the seismic moment and a high-frequency spectral level controlled by the seismic moment and a stress parameter. Awide range of spectral shapes can be obtained from these generalized spectral models, which makes them suitable for in- versions of data to obtain spectral models that can be used in ground-motion simu- lations in situations in which adequate data are not available for purely empirical determinations of ground motions, such as in stable continental regions. As an exam- ple of the use of the generalized source spectral models, data from up to 40 stations from seven events, plus response spectra at two distances and two magnitudes from recent ground-motion prediction equations, were inverted to obtain the parameters controlling the spectral shapes, as well as a finite-fault factor that is used in point- source, stochastic-method simulations of ground motion. The fits to the data are com- parable to or even better than those from finite-fault simulations, even for sites close to large earthquakes.