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Anomalous foreshock activity in southern California is associated with zones of high heat flow
  • Ester Manganiello,
  • Marcus Herrmann,
  • Warner Marzocchi
Ester Manganiello
University of study Naples Federico II, University of study Naples Federico II

Corresponding Author:ester.manganiello@unina.it

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Marcus Herrmann
University of Naples 'Federico II', University of Naples 'Federico II'
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Warner Marzocchi
The University of Naples Federico II, The University of Naples Federico II
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Foreshock analysis is expected to shed new light on the earthquake nucleation process and could potentially improve earthquake forecasting. Well-performing clustering models like the Epidemic-Type Aftershock Sequence (ETAS) model assume that foreshocks and general seismicity are generated by the same physical process, implying that foreshocks can be identified only in retrospect. However, several studies have recently found higher foreshock activity than predicted by the ETAS model. Here, we revisit the foreshock activity in southern California using different statistical methods and find anomalous foreshock sequences, i.e., those unexplained by ETAS, mostly for moderate mainshock magnitudes (magnitude 5.5 or smaller). The spatial distribution of these anomalies reveals that they preferentially occur in zones of high heat flow, which are known to host swarm-like seismicity. Outside these regions, the foreshocks generally behave as expected by ETAS. These findings may contribute to real-time detection of swarm-like activity and improve forecasting of large earthquakes.