Characterization of Fault Zones in Southern California by Analysis of Potency Tensor Summations
BAILEY, I.W., firstname.lastname@example.org, BECKER, T.W., email@example.com, and BEN-ZION, Y. firstname.lastname@example.org, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089
Seismic potency tensors provide a strain-based description of earthquake focal mechanisms and geometrical properties of an earthquake population can be described by summation of such tensors. We apply this method to populations of potency tensors for 0 < ML ‚â§ 5 southern California earthquakes recorded between 1984 and 2002. The tensors are computed from a focal mechanism catalog of ~170,000 events generated using the program HASH, with a preference for number of data over quality so as to retain wide spatial sampling and small-scale details. We compare summed tensors for populations defined by faulting region and earthquake magnitude in order to investigate the relation between earthquake characteristics and fault-related length scales. We investigate spatial scales ranging from 10 - 270 km and use the results to identify systematic differences between seismic behavior for different faults and different regions. Our results show features that are indicative of both scale-invariant and scale-dependent processes. Large faulting structures control the dominant sense of magnitude-independent deformation for a given region, while a hierarchy of smaller structures with wide ranging length-scales lead to local variations. However, significant differences between the CLVD components of the summed tensors, which we relate to fault heterogeneity, indicate systematic differences in deformation associated with earthquake populations from different fault zones or different magnitude ranges. We find an increase in heterogeneity associated with populations of smaller earthquakes, even when corrected for quality, and regions where faulting deviates strongly from the overall sense of deformation. This implies that variations in the orientation, complexity and size of faults exert notable control over resulting earthquake characteristics.