Modeling results

From the 3D waveform simulations, we found that the USGS model explains important features of the overall waveforms very well, but the synthetics arrive earlier than the observations at all distances. The records and synthetics were cross-correlated to determine the delay time (dt) for optimal alignment. (Figure 2.19). The cross-correlations of both P-waves and S-waves (Rodgers et al., 2007) show systematic delays indicating that on average the USGS 3D model is too fast.

Figure 2.19: Delay time dt is estimated by cross-correlating the data and synthetic waveform pairs in 0.1-0.5Hz. The time axis is relative to the reported origin time.
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Figure 2.20 shows the synthesized PGV in the 0.1-0.5 Hz in map view, and waveform comparisons in the 0.03-0.15Hz, 0.1-0.25Hz and 0.1-0.5Hz passbands for the Bolinas event. The synthetic PGV correlates well with the sedimentary basins and bedrock ridges, in that it is relatively larger in sedimentary basins and lower on bedrock ridges compared to what is computed with a 1D layered velocity structure and the same source parameters. For example, elevated shaking was observed in the distant Hollister valley as well as the San Francisco Bay region. The waveform comparison shows a very good fit in the 0.03-0.15 and 0.1-0.25Hz passband, except the POTR path. This west to east path crosses the northern San Francisco Bay area through the delta region, and evidently requires further model refinement. Waveform modeling of several paths crossing the region is ongoing.

Figure 2.20: (Top left) Synthetic PGV ShakeMap for the Bolinas earthquake in 0.1-0.5Hz passband. Comparison between the data (black) and synthetics (red) in 0.1-0.5Hz (Top right), 0.1-0.25Hz (Bottom left), and 0.03-0.15Hz (Bottom right).
\begin{figure*}\epsfig{file=ahyikim07_figure1.eps, width=16cm}\end{figure*}

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