Structural records and mechanical characteristics of seismic slip along an active fault crosscutting unconsolidated Quaternary sediments: Suryum fault, SE Korea

Geological Records of Coseismic Shear Localization Along the Yangsan Fault, Korea

“…Unit 1 in the PSZ, 20-500 μm in thickness, is a strongly foliated, shear localization zone (Figure 5a). Such a localization zone was generated in the experimental gouge sheared at 1.3 m s −1 (HVR4512, Figures 13 and 15) and has also been observed in the previous studies on clay-rich natural and experimental gouges (e.g., Boulton et al, 2017;Boutareaud et al, 2008;French & Chester, 2018;Han et al, 2014Han et al, , 2020Ujiie et al, 2011;Yao et al, 2013). The experimental reproductions of the localization structure at the seismic slip rates might indicate that the natural shear localization zone is possibly the coseismic origin, although similarly narrow shear localization zones have been observed to form at subseismic rates too.…”

“…From the observation at smaller scales, even much narrower slip zones, ranging from tens to hundreds of micrometers, have also been identified (e.g., Chester et al, 2003;De Paola et al, 2008;Han et al, 2020;Heermance et al, 2003;Kim et al, 2020). Similar shear localization has been reported from experimental work at seismic slip rates (e.g., Boutareaud et al, 2008;Brantut et al, 2008;Kitajima et al, 2010;Yao et al, 2013).…”

“…Another idea is that the shear localization in the clay‐rich gouge was possible due to pronounced dynamic fault weakening. Recent experimental and numerical studies have proposed that fault rupture nucleated at seismogenic depths can be propagated through clay‐rich gouges or sediments, due to dynamic fault weakening, even though the materials show velocity‐strengthening at subseismic slip rates (e.g., Faulkner et al., 2011; Han et al., 2020; Noda & Lapusta, 2013; Tanikawa & Shimamoto, 2009; Tarling et al., 2018; Ujiie et al., 2013). In experimental clay‐rich gouges dramatically weakened at seismic slip rates, narrow localization zones (thinner than several hundreds of μm) have been commonly observed (e.g., Boutareaud et al., 2008; Brantut et al., 2008; Ferri et al., 2011; Han et al., 2014; Kitajima et al., 2010; Ujiie et al., 2013; Yao et al., 2013).…”

“…The pinching out of Unit 1 material in Unit 2 indicates the former was injected into the latter. The structure has been observed in natural faults (e.g., Brodsky et al, 2009;Coppola et al, 2021;Fondriest et al, 2012;Han et al, 2020;Otsuki et al, 2003;Rowe et al, 2012;Smeraglia et al, 2017;Smith et al, 2011) and experimental gouges sheared at seismic slip rates (Han et al, 2020;Tanikawa et al, 2012;Ujiie et al, 2013). Therefore, the gouge fluidization and injection from Unit 1 into Unit 2 are highly likely to be caused by thermal fluid pressurization in Unit 1 during seismic slip.…”

“…Observation of fault cores of seismogenic faults at the outcrop scale reveals principal slip zones, which may be a few millimeters up to several centimeters in thickness (e.g., Chester & Chester, 1998; Sibson, 2003). From the observation at smaller scales, even much narrower slip zones, ranging from tens to hundreds of micrometers, have also been identified (e.g., Chester et al., 2003; De Paola et al., 2008; Han et al., 2020; Heermance et al., 2003; Kim et al., 2020). Similar shear localization has been reported from experimental work at seismic slip rates (e.g., Boutareaud et al., 2008; Brantut et al., 2008; Kitajima et al., 2010; Yao et al., 2013).…”