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Aftershock asymmetry on a bimaterial interface

Rubin, Allan M. and Ampuero, Jean-Paul (2007) Aftershock asymmetry on a bimaterial interface. Journal of Geophysical Research. Solid Earth, 112 (B5). Art. No. B05307. ISSN 2169-9313.

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To better understand the asymmetric distribution of microearthquake aftershocks along the central San Andreas fault, we study dynamic models of slip-weakening ruptures on an interface separating differing elastic half-spaces. Subshear ruptures grow as slightly asymmetric bilateral cracks, with larger propagation velocities, slip velocities, and normal stress changes at the rupture front moving in the direction of slip of the medium with the lower shear wave speed (the southeast front, in the context of the San Andreas). When the SE front encounters a stress barrier, the tensile stress perturbation behind the rupture front continues forward and for a wide range of barrier strengths nucleates a dying slip pulse. This slip pulse smooths the stress field and reduces the static stress change beyond the SE front. Furthermore, because the tensile stress that carried the slip pulse into the barrier is a purely dynamic phenomenon, the SE rupture front can be left far below the failure threshold, while the NW front remains quite close to failure. Both mechanisms could contribute to the observed aftershock asymmetry. Formation of a robust slip pulse requires a peak tensile stress perturbation that approaches the nominal strength drop of the slip-weakening law. To achieve this while minimizing off-fault damage requires either substantial velocity contrasts or small reductions in friction. The simulations also show a pronounced asymmetry in the timescales over which barriers to the SE and NW experience increasing stresses, a result that has implications for the asymmetric distribution of subevents in compound earthquakes.

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Ampuero, Jean-Paul0000-0002-4827-7987
Additional Information:© 2007 American Geophysical Union. Received 9 February 2006; accepted 31 January 2007; published 18 May 2007. Correction published 18 November 2007. We thank Alain Cochard for providing us with a numerical code that could handle basically anything we threw at it. An MPI version (BIMAT) is now available through the Orfeus Seismological Software Library ( We also thank Alain Cochard, Ruth Harris, and Ares Rosakis for their helpful reviews. This work was supported by NSF under grant EAR-0126184. This is ETH contribution 1483.
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:bimaterial interface; slip-weakening ruptures; aftershock asymmetry.
Issue or Number:B5
Record Number:CaltechAUTHORS:20100310-103559466
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Official Citation:Rubin, A. M., and J.-P. Ampuero (2007), Aftershock asymmetry on a bimaterial interface, J. Geophys. Res., 112, B05307, doi:10.1029/2006JB004337.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17719
Deposited On:11 Mar 2010 20:00
Last Modified:03 Oct 2019 01:32

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