Fault mirrors

2016-05-13 10:59:20

A number of physical and chemical mechanisms have been proposed to result in fault lubrication during earthquakes, based on both experimental data and theoretical considerations (e.g., flash heating of asperities, frictional melting, silica gel, nanopowder, and thermal decomposition) and are postulated to occur on natural faults (see Di Toro et al. [2011] and Niemeijer et al. [2012] for a summary). Solidified frictional melts, or pseudotachylytes, have been documented both in nature [e.g., Sibson, 1975; Swanson, 1992; Camacho et al., 1995; Di Toro and Pennacchioni, 2005] and in experiments [Spray, 1987; Tsutsumi and Shimamoto, 1997] and are commonly recognized as fossil earthquakes [Sibson, 1975; Di Toro et al., 2006]. Pseudotachylyte therefore has been used in many settings to infer the seismic nature of fault zones and allows the retrieval of key parameters related to the earthquake source [e.g., Di Toro et al., 2009]. However, with the exception of frictional melting evidence [Allen, 2005; Di Toro et al., 2006], only a few other potential indicators of seismic slip have been observed in nature [Kirkpatrick et al., 2013; Siman-Tov et al., 2013; Smith et al., 2013], which is a severe limitation in our understanding of earthquake physics.
Other proposed geologic evidence for seismic slip includes the combination of carbonate dissociation and fluid-rock interaction [Rowe et al., 2012a], thermally altered biomarkers [Polissar et al., 2011; Savage et al., 2014], thermally altered magnetic minerals [Evans et al., 2014], peculiar crystal-plastic features [Smith et al., 2013], injection of fluidized gouge [Rowe et al., 2012b], and fault mirrors (FMs) [Fondriest et al., 2013; Siman-Tov et al., 2013]. Fault mirrors (FMs) have been shown experimentally to form at seismic rates accompanied with thermal decomposition, nanograin coating and sintering, or recrystallization reaction [Han et al., 2007; Fondriest et al., 2013; Smith et al., 2013; Siman-Tov et al.
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