No abstract

Many subduction complexes exhumed from seismogenic depths are described as thick, turbidite-dominated sequences disrupted by duplexes and imbricate slices, and containing mélange shear zones defined by a foliated mudstone matrix surrounding clasts of more competent sandstone and/or basalt (e.g., the Chrystalls Beach,

Laboratory measurements can determine the potential for geologic materials to generate unstable (seismic) slip, but a direct relation between sliding behavior in the laboratory and physical characteristics observable in the field is lacking, especially for the phyllosilicate-rich gouges that are widely observed in natural faults. We integrated laboratory friction experiments with surface topography microscopy and demonstrated a quantitative correlation between frictional slip behavior and fault surface morphology of centimeter-scale samples. Our results show that striated, smooth fault surfaces were formed in experiments that exhibited stable sliding, whereas potentially unstable sliding was associated with rougher, isotropic fault surfaces. We interpret that frictional stability and fault surface morphology are linked via the evolution of asperity contacts on localized slip surfaces. If fault surface roughness obeys a fractal relationship over a large range of length scales, then we infer that the morphological characteristics observed in the laboratory could indicate the earthquake nucleation potential on natural fault surfaces.

Over the last few decades, slow slip events (SSEs) have been recognized in most major subduction zones worldwide (Schwartz & Rokosky, 2007). For this paper, we follow the definition of Bürgmann (2018) that an SSE is an aseismic slip transient with a duration of minutes to decades. SSEs have longer durations than low frequency (<1 s) and very low frequency (∼seconds) earthquakes (Ide et al., 2007), but in contrast to those types of slow earthquakes, SSEs do not emit detectable seismic waves. With the lack of a seismic signal, SSEs have been recognized mostly by the deployment of dense GPS networks, which measure the movement of the overriding plate. SSEs are identified as temporary episodes of the upper plate moving in the opposite direction of the subducting plate, signaling slip on the subduction interface (Dragert et al., 2001). Alternatively, SSEs can be indicated by migration of the nonvolcanic, episodic tremor that can accompany SSEs (Obara et al., 2004;Wech