UCLA

SKS arrivals from OBS data of the ALBACORE experiment (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) offshore Southern California are analyzed for shear wave splitting. In a region several hundred kilometers from the Pacific Plate, splitting directions are similar to on-land directions WSW-ENE and with similar delays 1.1-1.4 seconds. Three measurements give higher delays and also W-E directions. The directions are at 45 degrees to APM of the Pacific plate suggesting that either frozen-in anisotropy from paleo-spreading dominates over APM effects in the asthenosphere or that deeper mantle shearing has occurred unrelated to APM. A toroidal flow around slab rollback presents one such possibility.