Finally, a matched pair of filters was used to remove the short periods from the computed, deterministic recordings and to remove the long periods from the actual recordings, and these two filtered records were summed to produce the final ground motion. Figure 4 summarizes the overall pattern of peak velocities contoured over the computed grid. The peak ground displacements, velocities, and accelerations for 80 of the near-source grid stations nearest the source are tabulated in Table 1, with the horizontal components rotated to maximize the peak velocity. Examples of the simulated acceleration, velocity and displacement broadband time histories are given in Figure 5 along with spectral response. The largest ground velocities produced in the simulation are due to near-source effects, but they are also at soil sites where significant amplification occurs relative to rock sites.
Rupture starts at the hypocenter and propagates updip and to the north.
The regions where the extension of the buried thrust fault intersects the ground surface is where the most notable near-source directivity effects are found. Click here for Picture Figure 4. The basemap is southern California topography, with basins darkly shaded. However, the contours of the observed ground velocity are based on a irregularly spaced, coarsely-sampled observations, so the pattern is spatially aliased. In contrast, the predicted pattern is generated from a more finely sampled, uniform grid of stations and therefore it more adequately represents the ground velocity patterns in areas without observations.