• journal_title：Bulletin of the Seismological Society of America
• Contributor：Janice M. Murphy ; Gary S. Fuis ; Trond Ryberg ; William J. Lutter ; Rufus D. Catchings ; Mark R. Goldman
• Publisher：Seismological Society of America
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.1785/0120090004
• journal_abbrev：Bulletin of the Seismological Society of America
• issn：0037-1106
• volume：100
• issue：6
• firstpage：3194
• section：Articles

Structural details of the crust determined from P-wave velocity models can be improved with S-wave velocity models, and S-wave velocities are needed for model-based predictions of strong ground motion in southern California. We picked P- and S-wave travel times for refracted phases from explosive-source shots of the Los Angeles Region Seismic Experiment, Phase II (LARSE II); we developed refraction velocity models from these picks using two different inversion algorithms. For each inversion technique, we calculated ratios of P- to S-wave velocities (V_P/V_S) where there is coincident P- and S-wave ray coverage. We compare the two V_P inverse velocity models to each other and to results from forward modeling, and we compare the V_S inverse models. The V_S and V_P/V_S models differ in structural details from the V_P models. In particular, dipping, tabular zones of low V_S, or high V_P/V_S, appear to define two fault zones in the central Transverse Ranges that could be parts of a positive flower structure to the San Andreas fault. These two zones are marginally resolved, but their presence in two independent models lends them some credibility.

A plot of V_S versus V_P differs from recently published plots that are based on direct laboratory or down-hole sonic measurements. The difference in plots is most prominent in the range of V_P=3 to 5 km/s (or V_S∼1.25 to 2.9 km/s), where our refraction V_S is lower by a few tenths of a kilometer per second from V_S based on direct measurements. Our new V_S-V_P curve may be useful for modeling the lower limit of V_S from a V_P model in calculating strong motions from scenario earthquakes.