A seismic source model for continental France probabilistic seismic hazard assessment

Probabilistic seismic hazard assessment (PSHA) requires the definition of seismic source models (SSM) that describe the spatial variations of the seismic activity over the region of interest. They can include and combine active faults, seismotectonic area source polygons as well as zoneless, continuous descriptions of the seismicity. In this contribution, we present the different components of the source model we developed to update the probabilistic seismic hazard model for continental France that was published by Drouet et al. (2020).

Particular effort was dedicated to produce a new historical and instrumental catalogue, homogenized in moment magnitude, with location and magnitude uncertainty estimates. The three area source models used in the previous study were also revised in order to extend them up to 300 km away from the political borders so as to allow seismic hazard calculations at longer return periods. The recently published SSM of the ESHM20 was used to that end. We also explored new methodologies to build zoneless models with less arbitrary choices. Whenever possible, we involved Bayesian methodologies for the estimation of model parameters. Finally, a new feature for the updated seismic hazard map calculations is the introduction of active faults in the source model.

We present preliminary depth distributions, style of faulting, maximum magnitude and frequency magnitude estimates for the various elements of this source model. Location, but more importantly magnitude uncertainties are carefully taken into account and propagated at each stage to properly honor epistemic uncertainties in the subsequent seismic hazard calculations.