Moisture‐related weakening and strengthening of a fault activated at seismic slip rates

Abstract

From high‐velocity friction experiments on gabbro rock at a rate of 85 mm/s, we found that a fault with a thin gouge layer experienced slip weakening with a drop of about 80% in the friction coefficient. At room humidity conditions, the fault subsequently recovered its complete strength, over an interval of several minutes after the slip terminated. The strength recovery did not occur under dry N2 gas‐saturated condition. This result can be interpreted as the interaction of moisture with gouge particles: moisture‐drained weakening due to frictional heating and moisture‐absorbed strengthening due to cooling. This new mechanism can cause dynamic weakening of faults, which controls earthquake rupture propagation.

Use of a modified torsional Kolsky bar to study frictional slip resistance in rock-analog materials at coseismic slip rates

“…However, seismic inversions provide evidence that frictional resistance of major faults at co-seismic slip speeds (1-2 m/s) may be quite low (Heaton, 1990;Rice, 2006). Moreover, very little data exist for the simultaneously high slip rates and large slip displacements characteristic of co-seismic slip, and the data that do exist suggest that the frictional behavior at these slip speeds is dramatically different and the dynamic slip weakening occurs (Sibson, 1973;Tsutsumi and Shimamoto, 1997;Goldsby and Tullis, 2002;Di Toro et al, 2004;Mizoguchi et al, 2006;O'Hara et al, 2006). Rudnicki and Rice (2006), Segall and Rice (2006), Rempel and Rice (2006) and Rice (2006) have recently summarized two primary thermal weakening mechanisms which are assumed to act in combination during fault events: (1) flash heat-0020-7683/$ -see front matter Ó 2008 Elsevier Ltd. All rights reserved.…”

Slip weakening in rocks and analog materials at co-seismic slip rates

“…However, seismic inversions provide evidence that frictional resistance of major faults at co-seismic slip speeds ($1-5 m/s) may be quite low (Heaton, 1990;. Moreover, very little data exist for the simultaneously high slip rates and large slip displacements characteristic of co-seismic slip, and the data that do exist suggest that the frictional behavior at these slip speeds is dramatically different and the dynamic slip weakening occurs (Sibson, 1973;Tsutsumi and Shimamoto, 1997;Goldsby and Tullis, 2002;Di Toro et al, 2004;Mizoguchi et al, 2006;O'Hara et al, 2006). Rudnicki and Rice (2006), Segall and Rice (2006), Rempel and Rice (2006) and have recently summarized two primary thermal weakening mechanisms which are assumed to act in combination during fault events: (1) Flash heating and consequent weakening at highly stressed asperity contacts during rapid slip which reduces the friction coefficient, a phenomenon studied for many years as the key of understanding the slip rate dependence of dry friction in metals at high slip rates (Bowden and Thomas, 1954;Archard, 1958;Barber, 1976;Kuhlmann-Wilsdorf, 1985;Ashby et al, 1991;Irfan and Prakash, 1994), and which has also been considered recently in seismology as a mechanism that could be active in controlling fault friction during seismic slip before macroscopic melting (see also Andrews, 2002;Hirose and Shimamoto, 2005a;Wibberley and Shimamoto, 2005), and (2) Thermal pressurization of pore fluid within the fault core by frictional heating, which assumes the presence of water within shallow crustal fault zones, such that the effective normal stresss n (s n ¼ s n À p, where s n is the compressive normal stress on the fault, and p is the pore fluid pressure) controls frictional strength, and which reduces the effective normal stress and hence reduces the slip resistance associated with any given friction coefficient (Sibson, 1973;Lachenbruch, 1980;Smith, 1985, 1987;Lee and Delaney, 1987;Andrews, 2002;Wibberley, 2002;Noda and Shimamoto, 2005;Sulem et al, 2005).…”

Clay clast aggregates in gouges: New textural evidence for seismic faulting

“…Thermal dehydration of the fault gouge material [ Mizoguchi et al , 2006; Hirose and Bystricky , 2007; Brantut et al , 2008] appears to be a serious candidate to explain clay interlayer‐water removing and consecutive cortex structure collapse (i.e., radial compaction of the concentric dense layers) observed by EDX‐SEM, with a higher relative atomic density of Al, Mg, and Fe element in the CCA cortex.…”