Regional S-wave structure for southern California from the analysis of teleseismic Rayleigh waves

Abstract

Teleseismic Rayleigh waves, M_S > 7.0, in the period range 14 to 28 s, are well recorded by the short-period Benioff array within southern California. Multiple arrivals that hinder the determination of local phase velocity curves are detected by narrow band-pass filtering. The records are then windowed on distinct, coherent peaks that move uniformly across the array. Four to seven stations are included in the determination of both the phase velocity across the array and the incidence azimuth. For earthquakes in the western Pacific, the derived incidence azimuths are systematically rotated counterclockwise by 2–16°. Most of this rotation results from refraction at the continental shelf. Phase velocity data for both the southern Mojave—central Transverse Ranges and the Peninsular Ranges are inverted to obtain regional S-wave velocity models. The starting models are constructed from travel-time studies of local sources, both natural and artificial. Poisson's ratio as a function of depth is calculated for these two regions. The comparison of Poisson's ratio with laboratory ultrasonic studies requires a quartz-rich crust within the southern Mojave—central Transverse Ranges and a mafic crust within the Peninsular Ranges.