Aseismic slip on rate-weakening interfaces

Sohom Ray, & Dmitry I. Garagash

Published August 16, 2021, SCEC Contribution #11618, 2021 SCEC Annual Meeting Poster #172 (PDF)

We highlight how slow aseismic slip travels long distances on rate-weakening interfaces. We considered two model faults with sliding rate- and state-dependent interfacial shear strength: a thin deformable layer over a substrate and a slip surface within a full-space. The slip is driven by a tectonic dislocation (accrued at a constant rate at one end) on a finite fault with the other end either locked or free. We also consider scenarios where slip is driven by dislocations imposed at both the ends or spatially localized external stress.

Large faults: we find that initially locked faults exhibit a stable creep propagation over long distances along the fault before nucleating an instability in slip velocity. The creep run-out distances, before nucleating an instability, are considerably larger than the elasto-frictional nucleation length-scales inferred by linear stability analyses of steady-sliding [e.g., Rice and Ruina (1983), Rice(1993), Segall (textbook, 2010)] and predicted by nonlinear analysis of slip instabilities [e.g., Rubin and Ampuero (2005), Viesca (2016)]. After nucleation of the first dynamic rupture, the subsequent aseismic creep run-out distances are larger than the first creep event. The aseismic slip propagation, driven by a tectonic dislocation at one end, remains unaffected by conditions at the other end.

Finite faults of sizes larger than elasto-frictional nucleation length scales: the creep driven by dislocation at one end, with the other end free, traverse the whole fault and nucleates instability at the other end. The instability nucleates in the middle when tectonic dislocations drive slip at both ends. However, a strictly locked end has interesting consequences on dislocation-driven creep advance. In this case, the slow aseismic creep provokes instability only when the finite-fault size exceeds a cut-off size, Lc. Further, on such finite-faults of size larger than standard nucleation length-scales but lesser than the cut-off size, Lc, a propagating creep could fail to nucleate an instability, and instead, could continue to lock or exhibit a long sustained spatio-temporal type oscillation, breathing type evolution of slip rate. On the other hand, for a finite fault driven by dislocations at both the ends (or a finite-fault with free-surface at the other end), transition to instability does not involve such breathing type oscillation of slip rate.

Key Words
Creep, instability, earthquake nucleation, slow-slip

Citation
Ray, S., & Garagash, D. I. (2021, 08). Aseismic slip on rate-weakening interfaces. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)