Effect of mainshock selection, earthquake catalog and definition on foreshock rate estimates in Southern California

Khan, R. Azad, Werner, M. J., Biggs, J. and Fagereng, A. ORCID: https://orcid.org/0000-0001-6335-8534 2025. Effect of mainshock selection, earthquake catalog and definition on foreshock rate estimates in Southern California. Journal of Geophysical Research -Solid Earth 130 (7) 10.1029/2024JB030733 Item availability restricted.

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Abstract

Large earthquakes are sometimes preceded by smaller earthquakes (foreshocks), which may reveal the physical processes leading to large earthquakes. Identifying foreshocks in real-time might alert us to impending large earthquakes, potentially enabling short-term warning. Clear, accepted definitions of foreshocks, however, are lacking: Recent studies estimated that between 19% and 72% of large earthquakes in Southern California have foreshocks, each using different methods. Moreover, one study found a large increase in the foreshock rate in an “enhanced” catalog with many more small events, suggesting that foreshocks are detectable before more mainshocks with denser seismic networks and improved methods. In this study, we first recreate and explain this wide range of foreshock rates as a result of different definitions of foreshocks, different mainshock selection methods and several other method choices and data restrictions. Only one combination of choices leads to a large increase in the foreshock rate between the standard and enhanced catalog. Instead, our new preferred method, based on more robust choices, estimates ∼25% of mainshocks have foreshocks in the standard and enhanced catalog, respectively. Enhanced catalogs may thus not reveal foreshocks before significantly more mainshocks, placing new constraints on what controls foreshocks and the processes leading to large earthquakes.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Wiley
ISSN:	1934-8843
Funders:	NERC GW4+ Doctoral Training Partnership studentship from the Natural Environmental Research Council
Date of First Compliant Deposit:	20 June 2025
Date of Acceptance:	17 June 2025
Last Modified:	03 Jul 2025 09:52
URI:	https://orca.cardiff.ac.uk/id/eprint/179228

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