An improved tomographic model for southern California upper mantle seismic structure

We present new high-resolution P, S, and Vp/Vs tomography models of the upper mantle beneath California to better understand the current physical state and tectonic evolution. We improve on current seismic tomography models by including 3-D ray-tracing, ray weighting, and the use of SCEC's crustal model to make accurate crustal corrections. We also test some simple anisotropy models, such as a vertically aligned fast axis in the Transverse Ranges anomaly. Our models resolve greater amplitudes of upper mantle seismic structures than previously published models, and find the thickness of the Transverse Ranges anomaly to be reduced by about 10%. A general interpretation of the imaged structure indicates the high-velocity Transverse Ranges anomaly is abandoned Farallon slab (it is below the Pelona-Orocopia-Rand schist subduction complex) that descends beneath the Transverse Ranges, driving southern California crust into these ranges and helping to drive rifting in the Salton Trough. Low seismic velocities below the Salton Trough are a result of high temperatures and partial melting created by this rifting.