Evaluating the Statistical Significance of Foreshocks in Southern California Using the ETAS Model
Abstract
Events preceding large earthquakes are often referred as foreshock events. They may be the first precursory "grinds" before a large magnitude rupture and may help to understand the mechanism behind earthquake nucleation. Such foreshock sequences may also be explained by random cascades of events. The recent publication of a low completeness magnitude catalogue of Southern California (Quake Template Matching catalogue) is a motivation to reevaluate the variations of seismicity before mainshocks. A recent study suggested that 33 % of M ≥ 4 magnitude earthquakes in Southern California were preceded by an anomalous seismic productivity when considering a Poisson distribution of events (Trugman and Ross, 2019). When confronting these sequences against a Gamma distribution of inter-event times, Van Der Ende and Ampuero (2020) re-evaluated that only 18 % of earthquakes are preceded by an anomalous seismic productivity. These two studies use stationary models of seismicity and thus neglect the interactions between earthquakes. They do not consider the possibility of a cascade triggering scheme to explain the sequences observed. In this study, we confront the QTM catalogue against the non-stationary ETAS (Epidemic Type Aftershock Sequence) model of seismicity. In addition to simulating a background seismicity, this model takes into account the seismicity variations induced by the earthquake interactions. We use the temporal version of the ETAS model to detect anomalous seismic productivity before 47 mainshocks between 2008 and 2017. Productivity anomalies in the full 10-year local catalog were also investigated to evidence regions with a seismicity generally poorly explained by ETAS and adjust the significance of the foreshock detection. We find that only 4 out of the 47 foreshock sequences (9 %) present a significant ETAS anomalous productivity. All other foreshock sequences are well explained by cascades of foreshocks and background seismicity or occur in regions with recurrent productivity anomalies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT004.0005M
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 4317 Precursors;
- NATURAL HAZARDS;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS