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Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution

Inbal, Asaf and Clayton, Robert W. and Ampuero, Jean-Paul (2015) Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution. Geophysical Research Letters, 42 (15). pp. 6314-6323. ISSN 0094-8276. http://resolver.caltech.edu/CaltechAUTHORS:20150917-080641646

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Abstract

We use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in Long Beach, California. Poor signal-to-noise ratio due to anthropogenic activity is mitigated via downward-continuation of the recorded wavefield. The downward-continued data are continuously back projected to search for coherent arrivals from sources beneath the array, which reveals numerous, previously undetected events. The spatial distribution of seismicity is uncorrelated with the mapped fault traces, or with activity in the nearby oil-fields. Many events are located at depths larger than 20 km, well below the commonly accepted seismogenic depth for that area. The seismicity exhibits temporal clustering consistent with Omori's law, and its size distribution obeys the Gutenberg-Richter relation above 20 km but falls off exponentially at larger depths. The dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area. Because the event size distribution above 20 km depth obeys a power law whose exponent is near one, this improvement yields a hundred-fold decrease in the time needed for effective characterization of seismicity in Long Beach.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/2015GL064942DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2015GL064942/abstractPublisherArticle
ORCID:
AuthorORCID
Inbal, Asaf0000-0001-8848-7279
Clayton, Robert W.0000-0003-3323-3508
Ampuero, Jean-Paul0000-0002-4827-7987
Additional Information:© 2015 American Geophysical Union. Received 13 JUN 2015; Accepted 24 JUL 2015; Accepted article online 29 JUL 2015; Published online 13 AUG 2015. We thank Dan Hollis of Nodalseismic Inc for supplying the data used in this study and Signal Hill Petroleum for giving permission to use it. Comments from two anonymous reviewers have helped improve this manuscript. This work was supported by the NSF award EAR-1214912 and a THOR award that funded the mass-storage system for data archiving. The Editor thanks two anonymous reviewers for their assistance in evaluating this paper.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-1214912
Terrestrial Hazards Observation and Reporting CenterUNSPECIFIED
Record Number:CaltechAUTHORS:20150917-080641646
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150917-080641646
Official Citation:Inbal, A., R. W. Clayton, and J.-P. Ampuero (2015), Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution, Geophys. Res. Lett., 42, 6314–6323, doi:10.1002/2015GL064942
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60294
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:17 Sep 2015 19:53
Last Modified:24 Jan 2017 23:53

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