How much can off-fault deformation contribute to the slip rate discrepancy within the Eastern California Shear Zone?

Justin W. Herbert, Michele L. Cooke, Michael E. Oskin, & Ohilda Difo

Published 2014, SCEC Contribution #1754

Kinematic assumptions of geodetic inversions for fault slip require that the slip sums to the (plate) boundary velocity. This assumption neglects permanent off-fault deformation, which could account for discrepancies between geologic and geodetic estimates, such as across the Eastern California Shear Zone (ECSZ). We use three-dimensional mechanical models to assess if unaccounted permanent strain surrounding faults could contribute to slip rate discrepancies across disconnected faults within the ECSZ. We modified fault configurations derived from the Southern California Earthquake Center’s Community Fault Model to better represent the disconnected nature of active faults in the ECSZ. The models with revised fault geometry produce slip rates that better match geologic strike-slip rates, thus validating the revisions. Within these models, off-fault deformation accounts for 40 ± 24% of the total strain and accommodates 3.1 ± 1.8 mm/yr of plate-parallel velocity across the ECSZ. This suggests that a significant portion of the discrepancy between the geologic slip rates and rates from geodetic inversions in the ECSZ could owe to the inversion models’ assumption of zero permanent off-fault deformation.

Citation
Herbert, J. W., Cooke, M. L., Oskin, M. E., & Difo, O. (2014). How much can off-fault deformation contribute to the slip rate discrepancy within the Eastern California Shear Zone?. Geology, 42(1), 71-75. doi: 10.1130/G34738.1.