Effects of Nonplanar Fault Topology and Mechanical Interaction on Fault-Slip Distributions in the Ventura Basin, California

Abstract

To assess the control of fault geometry and mechanical interactions on fault-slip distributions in a complex natural system, we present results from threedimensional mechanical models incorporating both nonplanar and rectangular planar representations of active faults within the Ventura basin region of southern California. We find that the incorporation of geologically constrained nonplanar 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. The model results demonstrate that nonplanar 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 threedimensional mechanical models using realistic (i.e., nonplanar) fault geometry can be used to both predict slip rates at specific locations and determine whether existing sitespecific slip-rate estimates are representative of average fault-slip rates. Although geometric irregularities along-fault surfaces should resist slip, planar faults can have lesser slip than nonplanar 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.Online Material: Three-dimensional interactive fault mesh of Ventura region faults.

Paleoseismologic evidence for large-magnitude (Mw7.5–8.0) earthquakes on the Ventura blind thrust fault: Implications for multifault ruptures in the Transverse Ranges of southern California

“…Geodetically determined north-south convergence across the Ventura Basin is as rapid as 7-10 mm/yr (Donnellan et al, 1993a(Donnellan et al, , 1993bHager et al, 1999;Marshall et al, 2008Marshall et al, , 2013. The Ventura Avenue anticline, located on the north side of the basin (Fig.…”

Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California

“…Previous Poly3D models have constrained the geometry of active faulting in southern California by comparing the model results to uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011) and fault slip rates (e.g., Marshall et al, 2008;Cooke and Dair, 2011). Boundary-element method investigations of alternative fault confi gurations (e.g., Griffi th and Cooke, 2004;Marshall et al, 2008;Meigs et al, 2008;Dair and Cooke, 2009;Herbert et al, 2014) demonstrate that the three-dimensional fault geometry and connectivity exhibit fi rst-order effects on the distribution of deformation within these fault systems, including uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011).…”

“…Boundary-element method investigations of alternative fault confi gurations (e.g., Griffi th and Cooke, 2004;Marshall et al, 2008;Meigs et al, 2008;Dair and Cooke, 2009;Herbert et al, 2014) demonstrate that the three-dimensional fault geometry and connectivity exhibit fi rst-order effects on the distribution of deformation within these fault systems, including uplift patterns (Meigs et al, 2008;Cooke and Dair, 2011). Consequently, changes in fault geometry along the Coachella Valley segment of the San Andreas fault, and the inclusion of secondary faults in Indio and Mecca Hills, may exert a substantial infl uence on uplift within the region.…”

“…Previous mechanical modeling has demonstrated that complex fault geometry exerts a primary control on deformation (e.g., Marshall et al, 2008;Meigs et al, 2008). In southern California, plate interactions and fault structure are complex ( Fig.…”

An efficient finite element method for embedded interface problems

“…To avoid these challenges, many of these simulations either make simplifying assumptions on the topology or smear the fracture surfaces. However, as discussed in Bhat et al (2007) and Marshall et al (2008), these simplifying assumptions are likely to yield inaccurate results.…”