Towards a Harmonized Operational Earthquake Forecasting Model for Europe.

We develop a harmonized earthquake forecasting model for Europe based on the Epidemic-type Aftershock Sequence (ETAS) model to describe the spatio-temporal evolution of aftershock sequences. We propose a method modification that integrates information from the European Seismic Hazard Model (ESHM20) about the spatial variation of background seismicity during ETAS parameter inversion based on the expectation-maximization (EM) algorithm. Other modifications to the basic ETAS model are explored, namely fixing the productivity term to a higher value to balance the more productive triggering by high-magnitude events with their much rarer occurrence, and replacing the b -value estimate with one relying on the b -positive method to observe the possible effect of short-term incompleteness on model parameters. Retrospective and pseudo-prospective tests demonstrate that ETAS-based models outperform the time-independent benchmark model as well as an ETAS model calibrated on global data. The background-informed ETAS variant achieves the highest score in the pseudo-prospective experiment, but the performance difference to the second-best model is not significant. Our findings highlight promising areas for future exploration, such as avoiding the simplification of using a single b -value for the entire region or reevaluating the completeness of the used seismic catalogs. [ABSTRACT FROM AUTHOR]