Coseismic Surface Displacement in the 2019 Ridgecrest Earthquakes: Comparison of Field Measurements and Optical Image Correlation Results

Abstract

A first-order problem in earthquake studies is understanding the linkage between rupture at the surface and the underlying seismogenic fault. Specifically, what do spatial patterns of surface displacement reveal about fault rupture at seismogenic depths? For a number of historical surface rupturing earthquakes, deformation has been shown to be highly localized, for example in the 1940 Imperial Valley earthquake (Rockwell & Klinger, 2013). In contrast, other surface-rupturing earthquakes have produced highly distributed surface faulting patterns, with significant deformation distributed tens to hundreds of meters from the primary rupture traces (e.g., Gold et al., 2015; Rockwell et al., 2002; Zinke et al., 2019). Understanding the spatial patterns associated with localized versus distributed faulting has potential implications for magnitude-and length-displacement scaling relationships developed for surface-rupturing earthquakes (Wells & Coppersmith, 1994), as well as geologic investigations focused on characterizing displacement recorded by offset landforms used to calculate fault slip (

Large Surface‐Rupture Gaps and Low Surface Fault Slip of the 2021 Mw 7.4 Maduo Earthquake Along a Low‐Activity Strike‐Slip Fault, Tibetan Plateau

“…The magnitude of off‐fault deformation cannot be determined in this study due to lack of long, linear cultural markers across the surface‐rupture zone (Rockwell et al., 2002). In future work, a comparison of optical‐pixel correlation of pre‐ and post‐event satellite images with our geological measurements may provide some constraints on its magnitude (e.g., Gold et al., 2021; Milliner et al., 2015).…”

“…Taking InSAR results from He et al (2022) and Jin and Fialko (2021) as examples (Figure 4), our measurements are 2.5-2.7 m (on average) lower than the InSAR-based slip maximum; the ratio between our measurements and the slip maximum is <15%. Such reduced fault displacements also have been observed in other M w 7.0+ earthquakes (e.g., the 1992 Landers, 2010 El Mayor-Cucapah, 2010 Darfield and 2019 Ridgecrest events) that occurred on low-activity strike-slip faults, and can be explained by that (a) the fault slip did not totally propagate upward to the surface (named shallow-slip deficit; e.g., Fialko et al, 2005) and/or by that (b) the fault slip was distributed across a wide deformation zone and accommodated by off-fault deformation (e.g., Dolan & Haravitch, 2014;Gold et al, 2021;Milliner et al, 2015;Rockwell et al, 2002). For the Maduo earthquake, the coseismic slip pattern from InSAR data yields low shallow-slip deficit (Chen et al, 2021;He et al, 2022;Jin & Fialko, 2021;Xu et al, 2021): for example, in Jin and Fialko (2021) and He et al (2022), the InSAR-based slip near the surface is 2.2-2.6 m (on average), accounting for 70%-90% of the slip maximum; the shallow-slip deficit is only 10%-30% (Figure 4).…”

“…Such low‐activity faults commonly have spatially distributed faulting deformation and subtle topographic expression and, therefore, are difficult to map; some fault segments could be identified only after an earthquake (e.g., the 2010 M w 7.2 El Mayor‐Cucapah, Mexico event, the 2010 M w 7.1 Darfield, New Zealand event, and the 2019 M w 7.1 Ridgecrest, California event; Fletcher et al., 2014; Quigley et al., 2012; Xu et al., 2020). Moreover, limited fault slip at the surface (relative to that at depth) produced by each earthquake can make it easy to underestimate earthquake magnitude based on measurements of geomorphic offsets (e.g., the 1992 M w 7.3 Landers, California event and the 2019 M w 7.1 Ridgecrest, California event; Dolan & Haravitch, 2014; Gold et al., 2021; Milliner et al., 2015).…”

Surface slip variability on strike‐slip faults

“…Both McGill and Rubin (1999) and Milliner et al (2015) found a weak inverse correlation between the strength of near-surface material and the amount of distributed deformation for the 1992 Landers earthquake. Zinke et al (2014) also suggested that the strength of surficial material correlates with distributed deformation for the 2013 Balochistan earthquake, and Cheng and Barnhart (2021) found no correlation between distributed deformation and inelastic strain in this rupture. Because distributed deformation is likely an integral of multiple causes, fault maturity, fault strength, and slip in prior earthquakes may also play a role.…”

“…For the studies used in this analysis, image correlation can resolve displacements of 10% or less of the image pixel size (i.e. 10 cm for 1 m-resolution images) and profile stacking is used to further smooth out noise and increase signal-tonoise ratio (Gold et al, 2015(Gold et al, , 2021Milliner et al, 2015Milliner et al, , 2016bZinke et al, 2014). Synthetic tests also demonstrate that three different correlation algorithms can resolve displacement between 1/10th and 1/100th of the image pixel size with little noise, especially when pixels with low signal-to-noise ratio are masked out (Leprince et al, 2007;Rosu et al, 2015).…”