Testing Fault Models in Intraplate Settings: A Potential for Challenging the Seismic Hazard Assessment Inputs and Hypothesis?

Active faults in intraplate settings, exhibiting slow deformation, rarely expose clear morphotectonic expressions. In many cases, their characterization relies only on rare neotectonic slip rates, often integrated over the Holocene, Quaternary or Plio-Quaternary. In addition, the strain accumulated along these tectonic structures and therefore their locking depth and associated slip deficit usually remains out of reach of geodetic measurements. Finally, the micro-seismicity located in the vicinity of most of these structures usually fails in delineating clear active fault segments geometry. The seismogenic potential therefore remains tainted with large uncertainties. It is one of the main reasons why very little attention has been paid to testing how French seismicity compares to the predictions of tectonic models. In this work, focused on South-Eastern France, we confront the potentially active faults database of the French metropolitan territory with a recently published catalog of historical and instrumental seismicity. Seismicity rates are corrected for completeness biases and are then compared to the predictions of several endmember tectonic models. The rates of earthquakes predicted by the tectonic models appear six to eighteen times higher than the historical and instrumental observations. Such a difference could be explained by an overestimation of the seismogenic potential of the faults or by different average seismicity rates at historical and longer-term timescales. This variation, if genuine, could be implied by spatiotemporally clustered seismicity due to tectonic or non-tectonic modulations suggesting non-poissonian behavior of the largest earthquakes.