Flash weakening of serpentinite at near-seismic slip rates

Abstract

[1] To investigate the processes responsible for dynamic frictional weakening in antigorite serpentinite, we conducted single-velocity and velocity-stepping friction experiments at slip rates (V) from 0.01 to 0.4 m s −1 , sliding displacements up to 40 mm, and a normal stress of 5 MPa. Single-velocity experiments demonstrate an approximately 1/V dependence of friction on velocity above a characteristic weakening velocity V w ≈ 0.1 m s −1 , consistent with theoretical predictions for flash heating and subsequent weakening of asperities. Velocity-stepping experiments impose stepwise increases in slip rate show stepwise weakening at slip rates above V w . Scanning electron microscopy of experimental fault surfaces reveals nanoparticle gouge textures at raised sites (∼10 mm in diameter) in tests that exhibit dramatic weakening. Furthermore, X-ray diffraction analyses of fault gouge from the sliding surface document the formation of significant talc in these tests, indicating that weakening temperatures reached 500°C-700°C. In contrast, no talc is observed in samples for which V remained significantly below V w . The observed value for V w is consistent with published microphysical models for flash weakening when independent constraints on the thermal stability and contact strength of antigorite are considered. Finally, while serpentinite displays velocity-strengthening behavior at plate tectonic slip rates, our results indicate that seismic ruptures propagating into serpentinized regions in the shallow lithosphere may trigger seismicity or slow earthquakes, after limited amounts of displacement.

Mechanisms for Friction of Rock at Earthquake Slip Rates

“…The weakening occurs after a small slip displacement of about 1 mm. Similar behavior has been seen for granite, gabbro, a pure feldspar rock, a finegrained pure quartz rock, novaculite Roig Silva et al, 2004b), serpentine (Hirose and Bystricky, 2007;Kohli et al, 2011), and calcite marble (Han et al, 2007). After the velocity is reduced below 0.1 m s À1 , frictional strength returns to its typical quasi-static value within about 0.01 s ($2 mm of slip).…”

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

“…Thermal and physical properties from Schön [47] with M: Melnikov et al [48], C: Cermak and Rybach, [49]; B: Broz et al [50]; Be = Beeler [9]. K: Koholi et al [51].…”

Instabilities at frictional interfaces: Creep patches, nucleation, and rupture fronts

“…Using combined analytic and numeric tools we elucidate the physics of a sequence of instabilities at a frictional interface. In particular, we study the dynamics of slowly extending creep patches [39][40][41][42][43], their stability, and the emerging nonlinearly propagating rupture fronts.The model -The friction model we study is the realistic rate-and-state model introduced in [38], which is briefly presented here. The spatially-extended interface between two dry macroscopic bodies is composed of an ensemble of contact asperities whose total area A r is much smaller than the nominal contact area A n [44].…”

“…Using combined analytic and numeric tools we elucidate the physics of a sequence of instabilities at a frictional interface. In particular, we study the dynamics of slowly extending creep patches [39][40][41][42][43], their stability, and the emerging nonlinearly propagating rupture fronts.…”