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Open-File Report 2005-1317
Version 1.0

Compressional and Shear Wave Velocity Versus Depth in the San Francisco Bay Area, California: Rules for USGS Bay Area Velocity Model 05.0.0

By Thomas M. Brocher


x-y plot
Vs versus Vp for common rock types (from Figure 1)


This report summarizes and documents empirical compressional wave velocity (Vp) versus depth relationships for several important rock types in northern California used in constructing the new USGS Bay Area Velocity Model 05.0.0 []. These rock types include the Jurassic and Cretaceous Franciscan Complex (metagraywacke and greenstones), serpentinites, Cretaceous Salinian and Sierra granites and granodiorites, Jurassic and Cretaceous Great Valley Sequence, and older Cenozoic sedimentary rocks (including the La Honda basin). Similar relations for less volumetrically important rocks are also developed for andesites, basalts, gabbros, and Sonoma Volcanics. For each rock type I summarize and plot the data used to develop the velocity versus depth relationships. These plots document the existing constraints on the proposed relationships. This report also presents a new empirical Vp versus depth relation derived from hundreds of measurements in USGS 30-m vertical seismic profiles (VSPs) for Holocene and Plio-Quaternary deposits in the San Francisco Bay area. For the upper 40 m (0.04 km) these mainly Holocene deposits, can be approximated by Vp (km/s) = 0.7 + 42.968z - 575.8z2 + 2931.6z3 - 3977.6z4, where z is depth in km. In addition, this report provides tables summarizing these VSP observations for the various types of Holocene and Plio-Quaternary deposits. In USGS Bay Area Velocity Model 05.0.0 these compressional wave velocity (Vp) versus depth relationships are converted to shear wave velocity (Vs) versus depth relationships using recently proposed empirical Vs versus Vp relations. Density is calculated from Vp using Gardner's rule and relations for crystalline rocks proposed by Christensen and Mooney (1995). Vs is then used to calculate intrinsic attenuation coefficients for shear and compressional waves, Qs and Qp, respectively.

Download this report as a 58-page PDF document (of2005-1317.pdf; 1.8 MB)

For questions about the content of this report, contact Tom Brocher

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Maintained by: Michael Diggles
Date created: August 30, 2005
Date last modified: August 30, 2005 (mfd)