SCEC2025 Poster #138: Frictional behavior of partially water-saturated phyllosilicate-bearing gouge of mixed composition

Group B, Poster #138, Fault and Rupture Mechanics (FARM)

Frictional behavior of partially water-saturated phyllosilicate-bearing gouge of mixed composition

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Poster Presentation

2025 SCEC Annual Meeting, Poster #138, SCEC Contribution #14364 VIEW PDF

Phyllosilicates form an important group of silicate minerals characterized by a polymeric layered structure that results in unique hydro-mechanical properties. These sheet silicates exhibit distinct frictional behaviors in dry versus water-saturated states, implying substantial changes of fault strength with fluctuations of temperature and pore-fluid pressure. Given their prevalence in fault zones, the frictional behavior of phyllosilicates may exert important controls on the seismic cycle. Here, we present a constitutive law for the frictional behavior of partially water-saturated phyllosilicates of mixed composition under the hydrothermal and pressure conditions relevant to earthquake nucl...eation. The model explains the increase of the friction coefficient with effective normal stress of low-temperature, water-saturated phyllosilicates via osmotic pressurization at mineral surfaces around contact junctions. A mixing law provides in closed form the evolving frictional properties of heterogenous phyllosilicate-bearing gouge accompanying temperature and fluid-pressure dependent dehydration reactions. The model describes the conditions for substantial weakening of phyllosilicate-rich fault zones associated with hydrothermal activity, with implications for natural and anthropogenic seismic hazards.
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