Pervasive Foreshock Activity Across Southern California
- Creators
- Trugman, Daniel T.
- Ross, Zachary E.
Abstract
Foreshocks have been documented as preceding less than half of all mainshock earthquakes. These observations are difficult to reconcile with laboratory earthquake experiments and theoretical models of earthquake nucleation, which both suggest that foreshock activity should be nearly ubiquitous. Here we use a state‐of‐the‐art, high‐resolution earthquake catalog to study foreshock sequences of magnitude M4 and greater mainshocks in southern California from 2008–2017. This highly complete catalog provides a new opportunity to examine smaller magnitude precursory seismicity. Seventy‐two percent of mainshocks within this catalog are preceded by foreshock activity that is significantly elevated compared to the local background seismicity rate. Foreshock sequences vary in duration from several days to weeks, with a median of 16.6 days. The results suggest that foreshock occurrence in nature is more prevalent than previously thought and that our understanding of earthquake nucleation may improve in tandem with advances in our ability to detect small earthquakes.
Additional Information
© 2019 American Geophysical Union. Received 14 MAY 2019; Accepted 25 JUL 2019; Accepted article online 30 JUL 2019; Published online 8 AUG 2019. The two earthquake catalogs analyzed in the manuscript are publicly available online. The QTM catalog and the SCSN catalog are both archived by the Southern California Earthquake Data Center (scedc.caltech.edu/). We use publicly available heat flow data from Blackwell et al. (2011). Our calculations use open source Python software packages, including a wrapper of original Okada (1992) code (Thompson, 28 May 2014/2019). D. Trugman acknowledges institutional support from the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under Project 20180700PRD1. We are grateful to P. Johnson, I. McBrearty, and N. Lubbers for discussions while formulating the study, and we thank two anonymous reviewers and editor Gavin Hayes for insightful comments and suggestions that improved the manuscript.Attached Files
Published - Trugman_et_al-2019-Geophysical_Research_Letters.pdf
Supplemental Material - grl59386-sup-0001-2019gl083725-si.pdf
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Additional details
- Eprint ID
- 98043
- Resolver ID
- CaltechAUTHORS:20190820-133631627
- 20180700PRD1
- Los Alamos National Laboratory
- Created
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2019-08-20Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Seismological Laboratory, Division of Geological and Planetary Sciences