Offshore southern California lithospheric velocity structure from noise cross-correlation functions

Daniel C. Bowden, Monica D. Kohler, Victor C. Tsai, & Dayanthie S. Weeraratne

Published May 3, 2016, SCEC Contribution #7135

A new shear-wave velocity model offshore southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The ALBACORE ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, are used to measure ambient noise correlation functions and Rayleigh-wave dispersion curves which are inverted for 3D shear-wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now >200-km-wide continental shelf. Our velocity model suggests the persistence of uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground shaking simulations for risk estimates.

Bowden, D. C., Kohler, M. D., Tsai, V. C., & Weeraratne, D. S. (2016). Offshore southern California lithospheric velocity structure from noise cross-correlation functions. Journal of Geophysical Research, 121(5), 3415-3427. doi: 10.1002/2016JB012919.