We present a model for estimating horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The model provides predictive relationships for the orientation-independent average horizontal component of ground motions. Relationships are provided for peak acceleration, peak velocity, and 5-percent damped pseudo-spectral acceleration for spectral periods of 0.01–10 sec. The model represents an update of the relationships developed by Sadigh et al. (1997) and includes improved magnitude and distance scaling forms as well as hanging-wall effects. Site effects are represented by smooth functions of average shear-wave velocity of the upper 30 m (VS30) and sediment depth. The new model predicts median ground motion that is similar to Sadigh et al. (1997) at short spectral periods, but lower ground motions at longer periods. The new model produces slightly lower ground motions in the distance range of 10–50 km and larger ground motions at larger distances. The aleatory variability in ground motion amplitude was found to depend on earthquake magnitude and on the degree of nonlinear soil response. For large-magnitude earthquakes, the alea tory variability is larger than found by Sadigh et al. (1997).
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