Perfettini, H. and Avouac, J.-P. (2004) Postseismic relaxation driven by brittle creep: A possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks, application to the Chi-Chi earthquake, Taiwan. Journal of Geophysical Research B, 109 (B2). Art. No. B02304 . ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20101123-100006593
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We evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth, assuming a velocity-strengthening brittle creep rheology. We show that this model can help reconcile the time evolution of afterslip, as measured from geodesy, with aftershocks decay. We propose an analytical expression for slip of the brittle creeping fault zone (BCFZ) that applies to any dynamic or static stress perturbation, including shear stress and normal stress changes. The model predicts an initial logarithmic increase of slip with time. Postseismic slip rate decays over a characteristic time t_r = aσ/τ that does not depend on the amplitude of the stress perturbation, and it asymptotically joins the long-term creep imposed by interseismic stress buildup τ. Given that the seismicity rate might be considered proportional to the sliding velocity of the BCFZ, the model predicts a decay rate of aftershocks that follows Omori's law, with a mathematical formalism identical to that of Dieterich  although based on a different mechanical rationale. Our model also differs from Dieterich's model in that it requires that aftershock sequences and deep afterslip, as constrained from geodetic measurements, should follow the same temporal evolution. We test this for the 1999 Chi-Chi earthquake, M_w = 7.6 and find that both sets of data are consistent with a model of afterslip due to the response of the BCFZ. The inferred relaxation time t_r = 8.5 years requires a value for a = ∂μ/∂log(V) (μ being the coefficient of friction) in the range between 1.3 10^(−3) and 10^(−2).
|Additional Information:||© 2004 American Geophysical Union. Received 10 March 2003; revised 25 September 2003; accepted 31 October 2003; published 3 February 2004. Comments by Chris Marone, Nadia Lapusta, Hiro Kanamori, the Associate Editor, and an anonymous reviewer have greatly helped to improve this article. We thank Anne Loevenbruck and Rodolphe Cattin for discussion about the Chi-Chi earthquake, Jean Schmittbuhl for discussion about fault mechanics, and Christian Mariotti for discussion about brittle creep rheology.|
|Group:||Caltech Tectonics Observatory, Caltech Tectonics Observatory. Taiwan Tectonics and Seismicity|
|Subject Keywords:||postseismic relaxation; Omori law; Chi-Chi earthquake|
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|Official Citation:||Perfettini, H., and J.-P. Avouac (2004), Postseismic relaxation driven by brittle creep: A possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks, application to the Chi-Chi earthquake, Taiwan, J. Geophys. Res., 109, B02304, doi:10.1029/2003JB002488|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||10 Dec 2010 00:19|
|Last Modified:||26 Dec 2012 12:40|
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