Polarization Tomography for P-Wave Velocity Structure in Southern California

We develop a tomographic inversion method that uses teleseismic P wave polarization data to obtain velocity structure. Polarization inversion has some intrinsic advantages over travel Lime inversion: It is not influenced by source location and origin time errors; it is not sensitive to deep mantle velocity structure and can be used iteratively to improve the tomographic result. Polarization inversion is more sensitive to near-station velocity structure and to velocity gradient and is complementary to travel time inversion in this sense. The method is applied to California Institute of Technology-U.S. Geological Servey southern California array data. The result is generally consistent with previous work and also reveals that the high-velocity feature beneath the Transverse Ranges is bounded between 40 and 200 km depths and possibly has a second small piece at about 300 km depth. The slow velocity anomaly under the Salton Trough is limited to shallow depths, less than about 60 km.