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Earthquake nucleation in intact or healed rocks

Brantut, N; Viesca, RC; (2015) Earthquake nucleation in intact or healed rocks. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH , 120 (1) 191 - 209. 10.1002/2014JB011518. Green open access

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Earthquakes are generated because faults lose strength with increasing slip and slip rate. Among the simplest representations of slip-dependent strength is the linear slip-weakening model, characterized by a linear drop to a residual friction. However, healed fault rocks often exhibit some slip strengthening before the onset of weakening. Here we investigate the effect of such a slip-hardening phase on the initial growth of a slip patch and on the nucleation of rupture instabilities. We assume a piecewise linear strength versus slip constitutive relation. We compute stress and slip distributions for in-plane or antiplane rupture configurations in response to an increasing, locally peaked (parabolic with curvature κ) stress profile. In contrast with the strictly linear slip-weakening case, our calculations show that the curvature of the loading profile and the level of background stress strongly influence the nucleation size. Even for small amounts of slip hardening, we find that the critical nucleation size scales with inline image for κ[RIGHTWARDS ARROW]0, i.e., crack growth remains stable up to very large crack sizes for sufficiently smooth loading profiles. Likewise, when the background stress τb is very close to the initial strength τc, the critical crack size scales with inline image. An eigenvalue analysis shows that the nucleation length increases as the proportion of the crack undergoing slip hardening increases, irrespective of the details of the loading profile. Overall, our results indicate that earthquake nucleation sizes can significantly increase due to slip hardening (e.g., in healed fault rocks), especially when the background loading is smooth.

Type: Article
Title: Earthquake nucleation in intact or healed rocks
Open access status: An open access version is available from UCL Discovery
DOI: 10.1002/2014JB011518
Publisher version: http://dx.doi.org/10.1002/2014JB011518
Additional information: ©2014. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Keywords: earthquake, nucleation
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1467100
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