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Insights on earthquake triggering processes from early aftershocks of repeating microearthquakes

Lengliné, O. and Ampuero, J.-P. (2015) Insights on earthquake triggering processes from early aftershocks of repeating microearthquakes. Journal of Geophysical Research. Solid Earth, 120 (10). pp. 6977-6992. ISSN 2169-9313. doi:10.1002/2015JB012287.

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Characterizing the evolution of seismicity rate of early aftershocks can yield important information about earthquake nucleation and triggering. However, this task is challenging because early aftershock seismic signals are obscured by those of the mainshock. Previous studies of early aftershocks employed high-pass filtering and template matching but had limited performance and completeness at very short times. Here we take advantage of repeating events previously identified on the San Andreas Fault at Parkfield and apply empirical Green's function deconvolution techniques. Both Landweber and sparse deconvolution methods reveal the occurrence of aftershocks as early as few tenths of a second after the mainshock. These events occur close to their mainshock, within one to two rupture lengths away. The aftershock rate derived from this enhanced catalog is consistent with Omori's law, with no flattening of the aftershock rate down to the shortest resolvable timescale ∼0.3 s. The early aftershock rate decay determined here matches seamlessly the decay at later times derived from the original earthquake catalog, yielding a continuous aftershock decay over timescales spanning nearly 8 orders of magnitude. Aftershocks of repeating microearthquakes may hence be governed by the same mechanisms from the earliest time resolved here, up to the end of the aftershock sequence. Our results suggest that these early aftershocks are triggered by relatively large stress perturbations, possibly induced by aseismic afterslip with very short characteristic time. Consistent with previous observations on bimaterial faults, the relative location of early aftershocks shows asymmetry along strike, persistent over long periods.

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Ampuero, J.-P.0000-0002-4827-7987
Additional Information:© 2015 American Geophysical Union. Received 15 JUN 2015; Accepted 10 SEP 2015; Accepted article online 17 SEP 2015; Published online 9 OCT 2015. Data used in this study are from the Northern California Seismic Network, U.S. Geological Survey, Menlo Park ( We thank A. Rubin for numerous comments and Z. Duputel for discussion on the Metropolis algorithm. We thank the Associate Editor and reviewers Y. Kagan and B. Enescu for suggestions. We acknowledge funding from NSF (grant EAR-1015698).
Group:Seismological Laboratory
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Issue or Number:10
Record Number:CaltechAUTHORS:20160119-084659471
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Official Citation:Lengliné, O., and J. P. Ampuero (2015), Insights on earthquake triggering processes from early aftershocks of repeating microearthquakes, J. Geophys. Res. Solid Earth, 120, 6977–6992, doi:10.1002/2015JB012287
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63750
Deposited By: Tony Diaz
Deposited On:20 Jan 2016 00:56
Last Modified:10 Nov 2021 23:20

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