Moho depth variation in southern California from teleseismic receiver functions
The number of broadband three-component seismic stations in southern California has more than tripled recently. In this study we use the teleseismic receiver function technique to determine the crustal thicknesses and V-p/V-s ratios for these stations and map out the lateral variation of Moho depth under southern California. It is shown that a receiver function can provide ia very good "point" measurement of crustal thickness under a broadband::station and is not sensitive to crustal P velocity. However, the crustal thickness estimated only from the delay time: of the Moho P-to-S converted phase trades off strongly with the crustal V-p/V-s ratio. The ambiguity carl be reduced significantly by incorporating the later multiple converted phases, namely, the PpPs and PpSs+PsPs. We propose a stacking algorithm which sums the amplitudes of receiver Function at the predicted arrival ratios. This times of these phases by different crustal thicknesses: H and V-p/V-s ratios. This transforms the time domain receiver functions directly into the H-V-p/V-s domain without need to identify these phases and to pick their arrival times. The best estimations of crustal thickness and V-p/V-s ratio are found when the three phases are stacked coherently. By stacking receiver functions from different distances and directions, effects of lateral structural variation are suppressed, and an average crustal model is obtained. Applying this technique to 84 digital broadband stations in southern California reveals that the Moho depth is 29 km on average and varies from 21 to 37 km. Deeper Mohos are found under the eastern Transverse Range, the Peninsular Range, and the Sierra Nevada Range. The central Transverse Range, however, does not have a crustal root. Thin crusts exist in the Inner California Borderland (21-22 km) and the Salton Trough (22 km). The Moho is relatively flat at the average depth in the Western and central Mojave Desert and becomes shallower to the east under the Eastern California Shear;Zone (ECSZ), Southern California crust has an average V-p/V-s ratio of 1.78, with higher ratios of 1.8 to 1.85 in the mountain ranges with Mesozoic basement and lower ratios in the Mojave Block except for the ECSZ, where the ratio increases.