Effects of tectonic structures and long-term seismicity on paraglacial giant slope deformations: Piz Dora (Switzerland)

• Published in: Engineering geology 2019-12, Vol.263, p.105353, Article 105353
• Main Authors: Agliardi, Federico, Riva, Federico, Barbarano, Marta, Zanchetta, Stefano, Scotti, Riccardo, Zanchi, Andrea
• Format: Article
• Language: English
• Subjects: Deep-seated gravitational slope deformation; Deglaciation; Earthquake-induced landslides; FEM modelling; InSAR; Paraglacial slope failure
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2019.105353

•Analysis of DSGSD mechanisms in seismically-active areas.•Integrated structural, geomorphological, InSAR and 2D FEM modelling analysis.•Inherited structure associated to slope-scale folding pre-conditions slope evolution.•Deglaciation-related perturbations promoted DSGSD onset but not its full development.•Long-term seismicity stimulated DSGSD by recurrent earthquakes with Tr < 475yr. The interplay of tectonic and climatic forcing in the development of Alpine deep-seated gravitational slope deformations (DSGSD) is still poorly understood. We investigate a giant DSGSD affecting the Piz Dora slope (Val Müstair, Switzerland) by geological, structural and geomorphological analyses, spaceborne SAR interferometry and numerical modelling. The DSGSD affects Permian terrigenous and volcanoclastic successions folded into a kilometre-scale asymmetric anticline during the Alpine orogenesis. The area is characterized by active tectonic uplift and widespread shallow seismicity with dominant dip-slip fault mechanisms, experienced fast deglaciation after the Last Glacial Maximum and periglacial conditions between the Lateglacial and Holocene. The slope is affected by morpho-structural features testifying to the deep-seated gravitational sliding of 1.85km3 of rock along a basal shear zone over 400m deep. Analysis of rock glaciers and DInSAR data show that the DSGSD was active in Lateglacial times and is presently deforming at rates ö 15mm/yr. Integrated kinematic analysis of field and radar data outlines a key control of the inherited fold structure on the DSGSD, with a transition from deep compound sliding to the West, controlled by massive conglomerates (Chazforà Formation), to shallower roto-translational sliding to the East, controlled by volcanoclastic foliated rocks (Ruina Formation). 2DFEM stress-strain numerical models, simulating the post-LGM slope evolution in static, pseudo-static and dynamic conditions allowed evaluating the contribution of long-term seismicity to DSGSD in a paraglacial setting. Dynamic modelling was performed starting from the characterization of a real earthquake, representative of the recent local seismotectonic activity, and scaled to obtain dynamic scenarios with different return periods. Results suggest that deglaciation-related perturbations promoted the inception of the DSGSD but not its complete development, that was likely stimulated by the long-term contribution of recurrent, small earthquakes. Our results suggest that inherited str