Numerical investigation of the long-term influence of seismicity on the development of the Piz Dora DSGSD (Val Müstair, Switzerland)

The Piz Dora deep-seated gravitational slope deformation (DSGSD), located in Val Müstair (Eastern Switzerland), involves Austroalpine metasandstones, meta-conglomerates and phyllites folded into a slope-scale closed anticline. The surrounding area underwent significant deglaciation after the Last Glacial Maximum (LGM) and is subject to active tectonic uplifting and seismicity. While geological structure likely constrained DSGSD kinematics and size, the contribution of seismicity to rock slope instability in a deglaciating valley setting remains unclear. In this perspective, we performed series of numerical, 2D Finite- Element dynamic models. We accounted for the long-term effects of seismicity by testing different hypotheses, including aseismic conditions or dynamic loads corresponding to different hazard scenarios (i.e. reference peak ground accelerations corresponding to distinct return periods), applied at different stages during slope deglaciation and considering realistic earthquake inputs. Modelling results are consistent with field observations and suggest that long-term seismic action may have been required, in combination with post-glacial debuttressing, to lead complete development of observed mechanisms and magnitudes of gravitational deformations in a lithological and topographic context not completely favourable to DSGSD.