Calibration of the specific barrier model to earthquakes of different tectonic regions

The specific barrier model, proposed and developed by Papageorgiou and Aki (1983a,b; 1985) provides the most complete, yet parsimonious, self-consistent description of the faulting process. It applies both in the "near-fault" and in the "far-field" region, thus allowing for consistent ground-motion simulations over the entire frequency range and for all distances of engineering interest. The model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions (mainly eastern North America events), interplate regions, and regions of tectonic extension (Spudich et al., 1999, database). The ensemble average value of a key parameter of the specific barrier model, the local stress drop Delta sigma(L), is similar to 161 bars for interplate earthquakes, similar to 114 bars for extensional regime earthquakes, and similar to 180 bars for intraplate earthquakes. The high-frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self-similar scaling. The deviation is most likely caused by the "effective" source area and/or irregularities in the rupture kinematics. We account for their overall effects through a high-frequency source complexity factor, zeta, in the source spectrum of the specific barrier model. As a result, inter- and intraplate source spectra show similar high-frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger magnitudes. The interplate soil residuals show clear signs of nonlinear site response, whereas only slight signs of such nonlinearity are observed for the extensional dataset. The regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic, yet computationally efficient, way to model strong ground motions with implications for seismic hazard and risk analysis.