Damage zone heterogeneity on seismogenic faults in crystalline rock; a field study of the Borrego Fault, Baja California

Abstract

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Off‐Fault Damage Characterization During and After Experimental Quasi‐Static and Dynamic Rupture in Crustal Rock From Laboratory P Wave Tomography and Microstructures

“…We did not observe a clear trend between damage zone width and distance from rupture nucleation for dynamic and quasi‐static rupture (Figure 11c). The power law exponents of the highest‐quality power law fits vary between −0.37 and −0.49 for transects in both samples, these values are similar to those obtained for fault damage decay profiles in crystalline rock in the field (Ostermeijer et al., 2020; Savage & Brodsky, 2011).…”

“…The decrease in fracture density with distance may be described by a power law function or exponential function, as is often done for damage zone studies in the field and laboratory (e.g., Faulkner et al., 2011; Mitchell & Faulkner, 2009; Moore & Lockner, 1995; Savage & Brodsky, 2011; Ostermeijer et al., 2020). The intersection of such a fitted function intersects with the background fracture density threshold provides a damage zone width.…”

“…The similarity in Γ off and the difference in damage zone width is not caused by a difference in resolution; both this study as well as Moore and Lockner (1995) have a cutoff for fractures smaller than 3 μm. Possible explanations for the difference in damage zone widths are as follows: (1) Field and laboratory studies describe the evolution of fracture density in the fault damage zone by an exponential decay (Faulkner et al., 2011; Mitchell & Faulkner, 2009; Moore & Lockner, 1995), a logarithmic decay (Zang et al., 2000), or a powerlaw decay (Mayolle et al., 2019; Ostermeijer et al., 2020; Savage & Brodsky, 2011) with increasing fault‐perpendicular distance. This may result in different damage zone widths, but does not affect Γ off much as the “tail” of the damage zone does not contribute significant amounts of additional fracture damage.…”

Characterizing Near‐Field Surface Deformation in the 1990 Rudbar Earthquake (Iran) Using Optical Image Correlation

“…We also note that FZW estimates made from aerial photos may also be subject to the same geometry and correlation smoothing bias, and therefore even higher resolution data will be required to reliably capture the true widths. However, the FZW estimates from 1 m aerial photos for Zard Geli (Figure 16) are generally <50 m (when accounting for correlator and geometric smoothing), which is similar to those made for the 1992 Landers earthquake (Milliner et al., 2015) and 2016 Kaikoura earthquake (Zinke et al., 2019), as well as field‐based structural observations of damage zone widths (Mitchell & Faulkner 2009; Ostermeijer et al., 2020). This is likely because (1) the aerial photo correlations sample the damage zones with sufficient density to accurately capture real off‐fault deformation with minimal bias due to smoothing, and (2) at finer scales the amplitude of variability is smaller.…”

The Shear Deformation Zone and the Smoothing of Faults with Displacement

“…Faulkner et al, 2011;Savage & Brodsky, 2011;Vermilye & Scholz, 1998). The fracture density in this zone dies off as a power law with distance from the fault (e.g., Ostermeijer et al, 2020 and references therein). The dilatant damage zone width increases linearly with fault displacement, and typically levels out at several hundred meters for fault displacements exceeding several hundred meters (Savage & Brodsky, 2011); (iii) Including and extending beyond the dilatant damage zone is what we call the "shear deformation zone" (W S ; Fig.…”