The large seismographic network in Southern California provides a unique opportunity for studying seismic velocity variations within this tectonically active region, which includes a major plate boundary whose surface expression is the San Andreas Fault. In this study, the compressional velocity within the upper mantle beneath Southern California is investigated using observations of the dependence of teleseismic P‐wave delays at all stations on the distance and azimuth to the event. The variation of residuals with azimuth, which may be as large as 1.3 s at a single station, requires considerable heterogeneity within the upper mantle. Models for the velocity structure are derived from the delays by manual ray tracing and by automatic inversion techniques. These models are generally consistent, although the inversion technique leads to considerable smoothing, and include regions of low velocity beneath the Imperial Valley (∼ 30‐100 km depth; Δv/v∼ ‐ 4 per cent) and the central Mojave Desert and northern Salton Trough (∼ 100‐180 km; Δv/v 2.5 per cent) and high velocities beneath the south‐western Sierra Nevada (∼ 50‐180 km; Δv/v∼ 5 per cent) and much of the Transverse Ranges (‐50‐180 km; Δv/v∼ 4 per cent). The last observation is in good agreement with the findings of Hadley and Kanamori. No evidence is found for velocity differences across the San Andreas Fault at any depth, and there is no marked lithosphere—asthenosphere boundary; however, the velocity variations do correlate with the general tectonic provinces within Southern California. Copyright © 1980, Wiley Blackwell. All rights reserved
CITATION STYLE
Raikes, S. A. (1980). Regional variations in upper mantle structure beneath Southern California. Geophysical Journal of the Royal Astronomical Society, 63(1), 187–216. https://doi.org/10.1111/j.1365-246X.1980.tb02616.x
Mendeley helps you to discover research relevant for your work.