Enlighten the Triassic geological setting favourable to large gypsum dissolution-related collapses through geophysics. Case study of the Peyrui collapse (SE France).
Résumé
As part of an interdisciplinary scientific program aiming at analysing the phenomenon of gypsum dissolution and proposing risk management solutions, we used geophysics to answer the following question: what is the Triassic geological setting favourable to large gypsum dissolution-induced collapses? For that purpose we carried out two perpendicular ERT profiles around a major collapse occurred in 1992 in the area of the Peyrui (Var department, France). The interpretation of the geophysical results led us to better constrain the geological and structural scheme of the Peyrui collapse area. The collapse is located at the intersection of a N110° anticline and a major N10°-20° fault. We now considered this geological setting as a favourable context of both gypsum accumulation (anticline) and dissolution (water infiltration by the faults). The geophysical results also showed that the collapse might have modified the mechanical properties of the shallow depth formations that would be locally decompressed. Although we still poorly understood the mechanisms triggering the collapse, especially the role of the water, highlighting the favourable geological context constitutes a major step for risk management purposes. Through this case study, we clearly highlight that the geophysical imaging is a key tool for mapping areas prone to collapses formation.
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