The relation of crustal scattering to seismicity in southern California

Dense regional array recordings of 377 teleseismic events are used to map geographic variability in upper crustal P to S scattering in southern California. Scattered-wave energy is sensitive to short-wavelength heterogeneity and maps of scattering potential offer a powerful complement to travel time tomography in characterizing seismic crustal heterogeneity. The scale length of resolved scattering variability is commensurate with the scale lengths of surface fault-trace length and microseismicity variations, and both mapped faults and seismicity are concentrated in regions of strong scattering. Fault-proximal scattering averaged across-strike of predominately strike-slip fault zones is highly correlated with microseismicity levels and is predictive of the pattern of microseismicity variation but not of absolute scale. North-south profiles through the Transverse Ranges reveal coincident strong gradients in microseismicity and scattering, whereas mapped segment bounds along the San Andreas fault zone from San Francisco to the Salton Sea coincide with strong along-strike gradients in the level of scattering. The overall correlation of microseismicity and scattering potential is consistent with structural control of aftershock and background microseismicity production, strain energy control of scattering, or both. Prior evidence for fault offset in the pattern of scattering intensity [Revenaugh and Reasoner, 1997] favors the former.