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Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA

Hawthorne, J. C. and Simons, M. and Ampuero, J.-P. (2016) Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA. Journal of Geophysical Research. Solid Earth, 121 (11). pp. 8254-8275. ISSN 2169-9313.

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Postseismic slip observed after large (M > 6) earthquakes typically has an equivalent moment of a few tens of percent of the coseismic moment. Some observations of the recurrence intervals of repeating earthquakes suggest that postseismic slip following small (M ≾ 4) earthquakes could be much larger—up to 10 or 100 times the coseismic moment. We use borehole strain data from U.S. Geological Survey strainmeter SJT to analyze deformation in the days before and after 1000 1.9 < M < 5 earthquakes near San Juan Bautista, CA. We find that on average, postseismic strain is roughly equal in magnitude to coseismic strain for the magnitude range considered, suggesting that postseismic moment following these small earthquakes is roughly equal to coseismic moment. This postseismic to coseismic moment ratio is larger than typically observed in earthquakes that rupture through the seismogenic zone but is much smaller than was hypothesized from modeling repeating earthquakes. Our results are consistent with a simple, self-similar model of earthquakes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Simons, M.0000-0003-1412-6395
Ampuero, J.-P.0000-0002-4827-7987
Additional Information:© 2016 American Geophysical Union. Received 25 APR 2016; Accepted 8 OCT 2016; Accepted article online 12 OCT 2016; Published online 9 NOV 2016. Strain and creep data are provided by the United States Geological Survey and are available at The NCSN earthquake catalog is available at, through the Northern California Earthquake Data Center and the Berkeley Seismological Laboratory, doi 10.7932/NCEDC. Earthquake relocations were taken from Waldhauser [2009], also available through the NCEDC. The plotted fault traces are taken from the Quaternary fault and fold database for the United States, provided by the USGS and the California Geological Survey, and accessed from the USGS website Modeled atmospheric values are from the ECMWF model, available at [Dee et al., 2011]. Local atmospheric pressure data are from the Plate Boundary Observatory station B058, operated by UNAVCO with support from NSF, and available at This work was supported by a Caltech Division of Geological and Planetary Sciences Texaco postdoctoral fellowship to J.C.H. We thank Nadia Lapusta for interesting discussions. We are grateful to the Associate Editor, Andy Barbour, and an anonymous reviewer for comments that improved the paper.
Group:Seismological Laboratory
Funding AgencyGrant Number
Caltech Division of Geological and Planetary SciencesUNSPECIFIED
Subject Keywords:postseismic slip; repeating earthquakes; aseismic slip
Record Number:CaltechAUTHORS:20170201-153456109
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Official Citation:Hawthorne, J. C., M. Simons, and J.-P. Ampuero (2016), Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA, J. Geophys. Res. Solid Earth, 121, 8254–8275, doi:10.1002/2016JB013120
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73960
Deposited By: Tony Diaz
Deposited On:02 Feb 2017 01:02
Last Modified:02 Feb 2017 01:02

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