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Abstract We study the effects of pore fluid pressure (Pf) on the pre‐earthquake, near‐fault stress state, and 3‐D earthquake rupture dynamics through six scenarios utilizing a structural model based on the 2004Mw9.1 Sumatra‐Andaman earthquake. As pre‐earthquakePfmagnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop, and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre‐earthquakePfaverages near 97% of lithostatic pressure, leading to pre‐earthquake average shear and effective normal tractions of 4–5 and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co‐seismic principal stress rotations and absolute post‐seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with largerPfmagnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre‐earthquakePfdepth distribution. IfPffollows a sublithostatic gradient, pre‐earthquake effective normal stress increases with depth. IfPffollows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate updip. This renders constraints on near‐trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site‐specific measurements to constrain dynamically plausible megathrust strength andPfgradients.
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Thermobaric Activation of Fault Friction
Abstract The constitutive behavior of faults intervenes in virtually every aspect of the seismic phenomenon but is poorly understood, particularly regarding how effective normal stress affects the boundaries of the seismogenic zone. Here, we explore the mechanical properties of Pelona schist, Westerly granite, phyllosilicate‐rich gouge, gabbro, hornblende, lawsonite blueschist, montmorillonite, and smectite in hydrothermal conditions at various confining pressures and explain the laboratory observations with a physical model of fault friction. The thermobaric activation of healing and deformation mechanisms explains the boundaries of unstable slip as a function of slip‐rate, temperature, and effective normal stress for a given lithology. The constitutive law affords extrapolation of laboratory data in the conditions relevant to seismic cycles throughout the crust, explaining the focus of large earthquakes in collision, subduction, and continental and oceanic transform settings.
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- Award ID(s):
- 1848192
- PAR ID:
- 10580956
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 6
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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