Offshore Southern California lithospheric velocity structure from noise cross-correlation functions
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 Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3-D 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 the 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 the 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.
Additional Information© 2016 American Geophysical Union. Received 16 FEB 2016, Accepted 17 APR 2016, Accepted article online 20 APR 2016, Published online 3 MAY 2016. The authors thank Fan-Chi Lin for assistance with the initial signal processing, tilt and DPG corrections, and dispersion measurments; Yiran Ma for assistance with the 2-D inversions; and Rob Clayton, Asaf Inbal, Joann Stock, Simon Klemperer, and Sampath Rathnayaka for helpful discussions. The final model is available by contacting the corresponding author at email@example.com. SCSN data were provided by the Caltech/USGS Southern California Seismic Network at http://scedc.caltech.edu/ [California Institute of Technology, Caltech, 1926]. The OBS and DPG waveform data from the ALBACORE array are available from the IRIS Data Management Center at http://www.iris.edu/hq/. The IRIS Data Management System is funded through the National Science Foundation and specifically the GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation under Cooperative Agreement EAR-1063471. The OBS deployment was made possible with instruments and logistical support of the U.S. National Ocean Bottom Seismic Instrumentation Pool (OBSIP) at Scripps Institute of Oceanography; in particular, thanks go to Jeff Babcock, Ernie Aaron, Phil Thai, and Mark Gibaud. The OBS deployment and recovery cruises were made possible with the equipment and logistical support of the University-National Oceanographic Laboratory System (UNOLS) vessel fleet and staff support at Scripps with particular thanks to Jon Meyer, Brian Rowe, and Meghan Donohue. Kohler and Weeraratne thank Captain Curl and the crew of R/V Melville for assistance during the 2010 OBS deployment cruise and Captain Vullo and the crew of R/V New Horizon during the 2011 OBS recovery cruise. This work was supported by the National Science Foundation (grant OCE-0825254) and by USGS grant G14AP00074.
Supplemental Material - jgrb51593-sup-0001-SI.doc