| 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. |
