Evolution of slip surface roughness through shear

Abstract

A significant part of displacement in fault zones occurs along discrete shear surfaces. The evolution of fault surface topography is studied here in direct shear laboratory experiments. Matching tensile fracture surfaces were sheared under imposed constant normal stress and sliding velocity. The roughness evolution was analyzed using measurements of surface topography before and after slip. We show that shearing reduces the initial surface roughness at all measurement scales. At all wavelengths, the roughness ratio between initial and final roughness increases as a function of the slip distance. For a given test, the roughness ratio increases with wavelength up to a few millimeters, beyond which the ratio becomes wavelength independent. At this region the roughness measured after slip follows a power law similar to that of the initial tensile fracture surface. We interpret this geometrical evolution as a consequence of the deformation stage of interlocked asperities which is followed by shear-induced dilation.

The work budget of rough faults

“…While the modeling performed here, as highlighted again by W tot , shows an overall increase in mechanical efficiency as H approaches 1.0, there has been no such pattern observed in other studies. Faults, both natural and experimental, have demonstrated H-values that actually trend toward 0.8, roughly in the middle of our modeled range of self-affinity (e.g., Brodsky et al, 2010;Davidesko et al, 2014). While this is not directly explained by our analysis, as one can generate and simulate model faults of any value of H, regardless of how realistic the value is, it can be correlated to the nature of fractals themselves.…”

Cyclic Permeability Evolution During Repose Then Reactivation of Fractures and Faults

“…Fault permeability response is significantly dependent on contact matedness. Fault slip experiments and models with initially mated rough surfaces (artificially fractured or fabricated bare contact or densely packed gouge filled contact) show significant permeability enhancement with slip (e.g., Davidesko et al, ; Elsworth & Goodman, ; Fang et al, ; Wang et al., ). Conversely, when the fault is initially unmated, strong permeability reduction may result from the comminution of surface asperities (e.g., Broadky et al., ; Fang et al, ; Faoro et al, ; Zhang et al, ).…”

Smoothing of Fault Slip Surfaces by Scale‐Invariant Wear

“…This relation is, however, only weakly apparent in compilations of fault roughness analyses (Brodsky et al, ; Candela et al, ), perhaps due to the combination of disparate data sets from different tectonic settings and rock types. Laboratory experiments that imposed shear across preexisting fracture surfaces in limestone blocks find that the amplitude of roughness decreases by a roughly constant fraction regardless of length scale (Davidesko et al, ). However, similar experiments at higher normal loads instead produced rougher surfaces with slip (Badt et al, ).…”