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On the statistical significance of foreshock sequences in Southern California

van den Ende, M. P. A. and Ampuero, J.-P. (2020) On the statistical significance of foreshock sequences in Southern California. Geophysical Research Letters, 47 (3). Art. No. e2019GL086224. ISSN 0094-8276.

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Earthquake foreshocks may provide information that is critical to short‐term earthquake forecasting. However, foreshocks are far from ubiquitously observed, which makes the interpretation of ongoing seismic sequences problematic. Based on a statistical analysis, Trugman and Ross (2019, suggested that as much as 72% of all mainshocks in Southern California is preceded by foreshock sequences. In this study, we reassess the analysis of Trugman and Ross (2019,, and we evaluate the impact of the assumptions made by these authors. Using an alternative statistical approach, we find that only 15 out of 46 mainshocks (33%) are preceded by significantly elevated seismicity rates. When accounting for temporal fluctuations in the background seismicity, only 18% of the analyzed foreshock sequences remain unexplained by the background seismicity. These results imply that even in a highly complete earthquake catalog, the majority of earthquakes do not exhibit detectable foreshock sequences.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper Script
Ampuero, J.-P.0000-0002-4827-7987
Additional Information:© 2019 American Geophysical. Received 12 NOV 2019; Accepted 15 JAN 2020; Accepted article online 21 JAN 2020. The authors thank D. Trugman for sharing the details of the procedure and for in-depth discussion. MvdE thanks W. Ellsworth for discussion. The editor G. Hayes and two reviewers, A. Michael and D. Marsan, are gratefully acknowledged for their encouraging and constructive comments. This project is supported by French government through the UCA^(JEDI) Investments in the Future project managed by the National Research Agency (ANR) with the reference number ANR-15-IDEX-01. Python script that reproduce the data figures in this paper can be accessed at:
Group:Seismological Laboratory
Funding AgencyGrant Number
Agence Nationale pour la Recherche (ANR)ANR-15-IDEX-01
Subject Keywords:foreshocks; background seismicity; Southern California
Issue or Number:3
Record Number:CaltechAUTHORS:20191223-134941949
Persistent URL:
Official Citation:van den Ende, M. P. A., & Ampuero, J.‐P. (2020). On the statistical significance of foreshock sequences in Southern California. Geophysical Research Letters, 47, e2019GL086224.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100415
Deposited By: Tony Diaz
Deposited On:23 Dec 2019 21:54
Last Modified:05 Oct 2020 16:34

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