Anomalous foreshock activity in southern California is associated with
zones of high heat flow
Abstract
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.