Abstract
We investigate near-field ground-motion variability by computing the seismic wavefield for five kinematic unilateral-rupture models of the 1992 M (sub w) 7.3 Landers earthquake, eight simplified unilateral-rupture models based on the Landers event, and a large M (sub w) 7.8 ShakeOut scenario. We include the geometrical fault complexity and consider different 1D velocity-density profiles for the Landers simulations and a 3D heterogeneous Earth structure for the ShakeOut scenario. For the Landers earthquake, the computed waveforms are validated using strong-motion recordings. We analyze the simulated ground-motion data set in terms of distance and azimuth dependence of peak ground velocity (PGV). Our simulations reveal that intraevent ground-motion variability phi (sub ln(PGV)) is higher in close distances to the fault (<20 km) and decreases with increasing distance following a power law. This finding is in stark contrast to constant sigma-values used in empirical ground-motion prediction equations. The physical explanation of a large near-field phi (sub ln(PGV)) is the presence of strong directivity and rupture complexity. High values of phi (sub ln(PGV)) occur in the rupture-propagation direction, but small values occur in the direction perpendicular to it. We observe that the power-law decay of phi (sub ln(PGV)) is primarily controlled by slip heterogeneity. In addition, phi (sub ln(PGV)) , as function of azimuth, is sensitive to variations in both rupture speed and slip heterogeneity. The azimuth dependence of the ground-motion mean mu (sub ln(PGV)) is well described by a Cauchy-Lorentz function that provides a novel empirical quantification to model the spatial dependency of ground motion. Online Material: Figures of slip distributions, residuals to ground-motion prediction equations (GMPEs), distance and azimuthal dependence, and directivity predictor of ground-motion variability for different source models.