Combining updated structural and geophysical data into earthquake recurrence models for the SE of France

South-East France is found in a continental active tectonic domain where seismic activity is low to moderate and crustal deformation is slow, nevertheless historical seismic catalogs (Rovida et al., 2022) present about 10 Mw 5 and 1 Mw 6 events per century. In a region of such seismic activity the identification and characterisation of active faults is a challenging task, as neither seismicity nor surface deformation records (~ 1000 years of macroseismic data, ~ 60 years of instrumental seismicity, and ~ 25 years of GNSS acquisitions) provide conclusive evidence for larger events with long recurrence intervals (> 1000 years). Moreover the geological structure is complex due to the diverse tectonic history of the region. This results in the presence of a dense network of compound fault systems and difficults the identification of which faults are accommodating the deformation. This region has however been one of the most densely instrumented in France for over 20 years with seimic (Sismalp, Langlais et al., 2024)  and GNSS networks (Walpersdorf et al., 2018), hence, presenting a notable resolution of geophysical observations.

The aim of this study is to constrain earthquake recurrence models which exploit the vast amount of up-to-date geophysical and geological data with a culminating objective of PSHA (Probabilistic Seismic Hazard Assessment) for SE France. We present 2 earthquake source models. The first integrates main faults, in which we determine the geometry, potential maximum magnitude after empirical scaling relationships (Leonard et al., 2014) based on maximum length, potential slip rates based on a systematic analysis of local GNSS velocities and the resulting magnitude-frequency distributions. Fifteen faults are considered, critically selected from the newly built SEFPAF (South-East France Potentially Active Faults) catalog and combined with a smoothed seismicity model for off-fault earthquakes. The second source model is a 3 dimensional tectonic zonation which takes into account not only static criteria (geological maps and structures) but also dynamic criteria such as seismogenic depth (Sismalp; SIHex, BCSF-Rénass, 2022), seismic flux and maximum observed magnitudes (FCAT, Manchuel et al., 2017; ESHM20, Danciu et al., 2024), focal mechanisms (Mathey et al., 2020), surface strain derived from GNSS and InSAR (Piña-Valdés et al., 2022, Mathey et al., 2021), local stress derived from gravimetric models (Camelbeeck et al., 2014), the Moho depth derived from tomographic studies (Nouibat et al., 2022) and 3D geological models (Bienveignant et al., 2024). Once combined with ground motion models, these different source models will then be analysed in terms of resulting seismic hazard levels to better understand the impact of the hypotheses and assumptions underlying PSHA in this region.