A 3-D Crustal Tomography Model for Southern California from a Composite Event Method

Guoqing Lin, Peter M. Shearer, & Egill Hauksson

Published 2007, SCEC Contribution #1050

We present a new crustal seismic velocity model for southern California derived from P and S arrival times from local earthquakes and explosions. To reduce the volume of data and ensure a more uniform source distribution, we compute "composite event" picks for 2,597 distributed master events that include pick information for other events within spheres of 2 km radius. The approach reduces random picking error and maximizes the number of S-wave picks. To constrain absolute event locations and shallow velocity structure, we also use times from controlled sources, including both calibration shots and quarry blasts. We implement the SIMULPS tomography algorithm to obtain 3-D P and S velocity structure and hypocenter locations of the composite events. Our new velocity model in general agrees with previous studies, resolving slow velocity features at shallow depths in the basins and some fast velocity features in the mid-crust. Using our velocity model and 3-D ray tracing, we relocate about 450,000 earthquakes from 1981 to 2005. We observe a weak correlation between seismic velocities and earthquake occurrence, with shallow earthquakes mostly occurring in fast velocity regions and mid-crustal earthquakes occurring in slow velocity regions.

Key Words
heterogeneity, inversion, local earthquake tomography, locations, mantle, media, ranges, egion, station terms, wave

Citation
Lin, G., Shearer, P. M., & Hauksson, E. (2007). A 3-D Crustal Tomography Model for Southern California from a Composite Event Method. Bulletin of the Seismological Society of America,.