Impact of far-field glacially-induced stresses on fault stability in the eastern Paris Basin

Abstract

Stable Continental Regions (SCR) feature very low seismicity levels, but historical seismicity reveals that these areas can experience large damaging earthquakes of magnitude up to Mw ≈ 7, on faults that were previously undocumented or thought to be stable. Glacial Isostatic Adjustment (GIA) is commonly considered as a factor of SCR deformation and stress perturbations that can trigger fault failure in formerly glaciated areas. Studies suggest that fault reactivation due to GIA may not only be restricted to glaciated areas, but could also occur in their periphery, several hundreds of kilometers away from the former glaciations. In this study, we model GIA associated to the Alpine, Massif Central, Celtic and Scandinavian glaciations from the last glacial cycle, in order to estimate the impact of this process on fault stability in the eastern Paris Basin, an area featuring very low strain rates and seismic activity, but of particular interest due to the proposed construction of a radioactive waste disposal facility. Our computations predict stress perturbations far (hundreds of kilometers away) from the ice loads, of similar amplitude to those in areas where fault reactivation has been observed (1–8 MPa at LGM, 0.8–2 MPa at present-day in our study area). We also show that the interaction between several GIA systems can impact the timing of maximum fault destabilization in a different way than common models considering only a single ice load. The computed far-field glacially-induced stress perturbations remain small compared to ambient crustal stresses, but they are large enough to potentially destabilize faults close to Andersonian geometries, with known faults in the eastern Paris Basin meeting these criteria, mainly in the Marne and Saint-Martin-de-Bossenay fault systems. Yet, there is no known evidence of Quaternary fault activity in the Paris Basin, and discrepancies between the localization of potentially unstable faults due to GIA and seismically active areas in northern France suggests that other processes must be at play.