Deformation processes adjacent to active faults: Examples from eastern California

Abstract

[1] Major seismogenic faults are embedded within narrow zones of inelastic off-fault deformation (OFD), where both distributed displacement and modification of rock properties occur. Active distributed displacement may affect slip rate estimates, seismic energy radiation and geodynamic models. This study addresses the role of OFD in the displacement history and mechanical behavior of seismogenic faults, by multisite study of deformed geologic features adjacent to 30-60 km long active strike-slip faults of <10 km of dextral displacement in the Mojave Desert, eastern California. We find that distributed displacement accommodates 0 to ∼25% of the total displacement over zones of one to two kilometers width. Displacement occurs mostly within 100-200 m of faults and decreases nonlinearly away from the main fault. We show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the Calico fault. We also find evidence for shear via rotation and progressive fragmentation adjacent to the Harper Lake fault. Analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10. Based on crosscutting relationships and the relationship of OFD to geophysically imaged compliant zones around active faults, we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault.Citation: Shelef, E., and M. Oskin (2010), Deformation processes adjacent to active faults: Examples from eastern California,

Off-fault long-term damage: A condition to account for generic, triangular earthquake slip profiles

“…We impose the damage zone to have different widths (W) ranging from ∼3 to 50% of the fault length. It is important to note that, although it has long been supposed that damage was confined only within a very narrow zone around the faults [ Li et al ., ; Ben‐Zion et al ., ; Fialko , ; Fielding et al ., ; Mitchell and Faulkner , ], an increasing number of observations suggests that it might rather extend over large areas up to several kilometers [ Spudich and Olsen , ; Manighetti et al ., ; Oskin et al ., ; Cochran et al ., ; Barbot et al ., ; Shelef and Oskin , ; Griffith et al ., ; Smith et al ., ]. Several studies have suggested that the damage zone width might scale linearly with the fault length and/or displacement [ Scholz et al ., ; Knott et al ., ; Vermilye and Scholz , ; Beach et al ., ; Manighetti et al ., ; Savage and Brodsky , ], but the actual ratios between damage zone width and fault length are still poorly known.…”

Surface slip and off‐fault deformation patterns in the 2013 MW 7.7 Balochistan, Pakistan earthquake: Implications for controls on the distribution of near‐surface coseismic slip

“…Overall, our comparison of strain localization with surface material type strongly suggests that, given sufficiently thick sediments, there is a correlation between percent OFD and material type, as suggested by models [e.g., Ma , ; Ma and Andrews , ; Kaneko and Fialko , ] and field observations [e.g., Treiman et al ., ; Shelef and Oskin , ; Van Dissen et al ., ; Oskin et al ., ; Duffy et al ., ; Dolan and Haravitch , ]. The precise degree of influence that near‐surface material properties and thickness have on strain localization provides fertile ground for future research, and many more observations such as those detailed above from other specific ruptures are needed.…”

TheM7 2016 Kumamoto, Japan, Earthquake: 3‐D Deformation Along the Fault and Within the Damage Zone Constrained From Differential Lidar Topography

“…The near‐fault regions that deformed inelastically in the 2016 earthquake likely spatially overlap with the compliant fault damage zone created by many past ~ M 7 earthquakes on the FHFZ. Future imagery differencing at still‐higher spatial resolution may facilitate examining whether the fault zone is best described as a block model with decreasing block dimension and material rigidity toward the principal fault (e.g., Shelef & Oskin, ) or as a broad shear belt with areas of localized deformation (e.g., Johnson et al, ).…”