A review of the Epidemic Type Aftershock Sequences (ETAS) model: 30 years of modeling seismicity

Earthquakes seldom come alone. They occur in temporal and spatial clusters, occasionally preceded by foreshocks, always followed by aftershocks, and sometimes they occur in complex multi-mainshock earthquake cascades that can last decades. Although individual earthquakes remain unpredictable, the average properties of earthquake clustering are well described by empirical relations, such as the Omori law for the decay of aftershocks with time, the Utsu-Seki scaling law for the aftershock productivity with mainshock magnitude, and the Gutenberg-Richter distribution of magnitudes. The Epidemic Type Aftershock Sequences (ETAS) model combines these and other empirical relations in a flexible stochastic point-process model, first conceived in 1988 by Yosi Ogata to describe secondary aftershock triggering. Over the past thirty years, the ETAS model has become the most popular model of clustered seismicity. Beyond academic research, the model is now also used for public earthquake forecasting by several national government agencies. In this talk, I will introduce the model, review some of its applications, and highlight current seismological and methodological controversies. Parameter estimation and the influence of calibration data quality remain thorny issues, which data assimilation techniques may be able to help address.

Invited by Gert Zöller.