Mechanics, slip behavior, and seismic potential of corrugated dip‐slip faults

Abstract

[1] To better understand the mechanics and seismic potential of nonplanar fault surfaces, we present results from a suite of numerical models of faults with sinusoidal corrugations in the downdip direction. Systematic variations in corrugation wavelength, amplitude, and loading angle are introduced to determine the effects on slip behavior and seismic moment release. We find that corrugated faults, in general, slip less than planar faults. Changes in slip behavior are nearly scale-independent and are dominantly controlled by the amplitude/wavelength of corrugations. Model results suggest that obliquely loaded corrugated faults accumulate less strike slip than a planar fault with the same tip line dimensions and average orientation. This result implies that slip direction is not a reliable indicator of regional stress direction and may at least partially explain repeated, nearly pure dip-slip coseismic events at oblique plate boundaries. Though the scalar seismic moment release is always less for corrugated fault surfaces due to a greater reduction in slip compared to increased surface area, for geologically reasonable corrugation geometries, changes in total scalar moment release are not significantly different than planar faults. Techniques that utilize highly simplified fault geometries may therefore accurately reproduce scalar moment release but will nonetheless incorrectly predict coseismic slip magnitudes and distributions, as well as regional stress orientations.Citation: Marshall, S. T., and A. C. Morris (2012), Mechanics, slip behavior, and seismic potential of corrugated dip-slip faults,

The work budget of rough faults

“…As faults tend to evolve toward smoother geometries with slip (Ben-Zion and Sammis, 2003;Lyakhovsky et al, 2001;Marshall and Morris, 2012), one can view faults described by higher H as more "mature" than those faults with higher β and lower H. This may also be true for lower β, however not all previous models and observations of cumulated slip on faults observe this phenomena (e.g., Candela et al, 2009;Candela et al, 2011b;Power and Tullis, 1991). As predicted by Cooke and Murphy (2004), these more mature faults indeed have lower W int and higher W grav , with a smaller overall total work budget, signifying that these faults are more mechanically efficient than their self-affine and rougher counterparts.…”

“…Fault roughness is thought to develop by the irregular linkage of smaller fault segments (Ben-Zion and Sammis, 2003;Walsh et al, 2003), and evolves by linkage and abrasive wear during individual slip events integrated over time (Marshall and Morris, 2012;Sagy et al, 2007). More mature and smoother faults are thought to be mechanically more efficient (Cooke and Murphy, 2004).…”

Paleostress inversion: A multi-parametric geomechanical evaluation of the Wallace–Bott assumptions

“…Some natural faults present sinusoidal surfaces like the Flowers Pit Fault, Oregon (Sagy and Brodsky, 2009;Sagy et al, 2007), the sub vertical strike-slip faults in the central Sierra Nevada, California, (Griffith et al, 2009) and the Arkitsa fault surface with 1 to 5 m corrugations (Resor and Meer, 2009). The 3D undulations of the fault surface (Power et al, 1987;Lee and Bruhn, 1996) are thought to be influential in term of mechanical behavior of slip during its reactivation (Marshall and Morris, 2012;Chester and Chester, 2000;Saucier et al, 1992).…”

“…Pollard et al (1993) predicted a maximum of 37° discrepancy angle for fault interaction and a 10° misfit angle caused by fault tip geometry. Marshall and Morris (2012) used a mechanical model to show that slip vectors on currugated faults closely parallel the corrugation direction and not the remote loading direction.…”

“…Following these observations, a second geometric configuration has been studied. It includes corrugated faults with increasing amplitude to wavelength ratio (Am), which is given by the formulation of Ritz and Pollard (2012), and Marshall and Morris (2012).…”