Publication Date:
2023-02-01
Description:
While sliding at seismic slip-rates of ∼1 m/s, natural faults undergo an abrupt decrease of shear
stress called dynamic weakening. Asperity-scale (〈〈mm) processes related to flash heating and weakening
and, meso-scale (mm-cm) processes involving shear across the bulk slip-zone, related to frictional melting
or viscous flow of minerals, have been invoked to explain pronounced velocity-dependent weakening. Here
we present a compilation of ∼100 experiments performed with two rotary shear apparatuses. Cohesive rock
cylinders of basalt, gabbro, granitoid rocks and calcitic marble were sheared at various values of effective
normal stress (σneff = 5–40 MPa), target slip-rate (Vt = 0.1–6.5 m/s) and fluid pressure (Pf = 0–15 MPa). To
account for the uncertainties of constitutive parameters, we introduce a norm-based optimization procedure
on a set of model parameters by comparing the shear stress evolution inferred from the proposed weakening
models with the shear stress measured during the experiments. We analyze the fit to experimental data of
each weakening model and we discuss a composite model in which two weakening mechanisms (namely flash
heating and bulk melting, flash heating and dislocation/diffusion creep) are used to test the hypothesis that
they match the shear stress evolution in different slip ranges. We found that for slip smaller than a slip-switch
distance δ0, the weakening is better described by mechanisms occurring at the asperity scale whereas for larger
slip values the bulk model performs better. The inferred δ0 values decrease with normal stress suggesting that
during earthquakes bulk mechanisms can govern shear stress evolution after a few centimeters of slip.
Description:
Published
Description:
e2022JB024356
Description:
3T. Fisica dei terremoti e Sorgente Sismica
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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