Consistency between a Strain Rate Model and the ESHM20Earthquake Rate Forecast in Europe: insights for seismic hazard

Most national and international seismic regulations require quantifying seismic hazard based on probabilistic seismic hazard assessment (PSHA) methods. The probabilities of exceeding ground-motion levels at sites of interest over a future time window are determined by combining a source model and a ground-motion model. Earthquake catalogs, merging instrumental and historical data, are usually used to establish earthquake recurrence models. Although these catalogs extend over several centuries, the observation time windows are often short with respect to the recurrence times of moderate-to-large events and in some regions the recurrence models can be weakly constrained.

In the present work, we take advantage of two new studies conducted at the scale of Europe: the latest release of the probabilistic seismic hazard model for Europe (ESHM20, Danciu et al. 2021); and the strain rate maps computed by Piña-Valdés et al. (2022). Our objective is to test the compatibility between the ESHM20 model and the geodetic dataset from a moment comparison perspective, examining how geodetically-observed deformation relates to seismic strain release.

We computed the seismic and geodetic moment distributions, as well as the overlap between them in polygons, called source zones, defined in ESHM20. We assume that an overlap higher than 35% indicates compatibility between the two models.

Our results show that in areas characterized by high activity, such as the Betics, the Apennines, the Dinarides, and the eastern Mediterranean, the moment rates derived by both methods are generally compatible. In these regions, the different spatial scales between geodesy and seismicity can trigger local incompatibility, but this effect can be neglected with the use of wider zones.

However, areas characterized by low to moderate activity show different behavior. In the Fennoscandia source zones affected by GIA, the two models are not compatible. In the rest of intracontinental Europe, the compatibility between the two models depends on whether they are well-constrained or not.

These findings contribute to understanding what portion of tectonic deformation results in earthquakes across different tectonic contexts, and how spatial scale and data constraints affect this assessment.