Effects of Non-Planar Fault Topology and Mechanical Interactions on Fault Slip Distributions

Scott T. Marshall, Michele L. Cooke, & Susan E. Owen

Published 2008, SCEC Contribution #1108

To assess the control of fault geometry and mechanical interactions on fault slip distributions in a complex natural system, we present results from three-dimensional mechanical models incorporating both non-planar and rectangular planar representations of active faults within the Ventura basin region of southern California. We find that the incorporation of geologically-constrained non-planar fault surfaces into numerical models of active deformation results in a better match to available geologic slip rate data than models utilizing rectangular planar fault surfaces. We find that non-planar fault geometry and mechanical interactions exert a strong control on resultant slip distributions. Additionally, we find that slip rates at most locations along the surface trace of Ventura faults are not likely to represent average values for the entire fault surface. We propose that results from three-dimensional mechanical models using realistic (i.e. non-planar) fault geometry can be used to both predict slip rates at specific locations and determine whether existing site-specific slip rate estimates are representative of average fault slip rates. Although geometric irregularities along fault surfaces should resist slip, we find that planar faults can have lesser slip than non-planar faults due to the differing mechanical interactions among nearby faults in the two representations. This suggests that models using simplified or planar fault geometry are likely to inaccurately simulate regional deformation. We assert that detailed knowledge of three-dimensional fault shape as well as the geometry and configuration of deep fault intersections is essential for accurate seismic hazard characterization of regions of complex faulting such as the Ventura basin of southern California.

Key Words
United States, orientation, Global Positioning System, technology, time series analysis, three-dimensional models, statistical analysis, slip rates, mechanical properties, strike-slip faults, deformation, geometry, California, Ventura Basin, neotectonics, seismicity, seismic risk, movement, velocity, risk assessment, tectonics, active faults, earthquakes, faults

Marshall, S. T., Cooke, M. L., & Owen, S. E. (2008). Effects of Non-Planar Fault Topology and Mechanical Interactions on Fault Slip Distributions. Bulletin of the Seismological Society of America, 98(3), 1113-1127. doi: 10.1785/0120070159.