Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

I N T R O D U C T I O N The Montagne du Vuache Fault (MVF) is a major fault system extending over ~80 km long from the edge of the Alpine range to the Jura Mountains (calcareous rocks), through the southernmost Swiss Molasse basin (sandstones and siltstones). The recent tectonics of the MVF have been studied in its southeastern part, following the damaging Epagny earthquake near Annecy (13/07/1996; MI = 5.3;(Thouvenot et al., 1998)) (Fig. 1). While theQuaternary left-lateral faultinghasbeenconfirmedthere (e.g. displacement of small valleys, syn-depositional deformation, etc.) (Baize et al., 2011; De La Taille, 2015), these studies have not yet demonstrated the occurrence of surface-rupturing events during the last thousands of years. As the fault extends northwesterward into the Jura mountains, it splits into multiple segments. In this area, the youngest evidence of fault activity at the surface relies on syntectonic mineralized calcites which were dated with U-Pb method, indicating a main phase at around 10 Myr, followed by a reactivation phase at ~5 Myr (Smeraglia et al., 2021). To improve our knowledge of the recent seismotectonic activity in this area, we have conducted a multidisciplinary and multiscalar approach combining structural geology, geomorphology, and analysis of the deformation on archeological remains. At the distance of ~60 kmwest of Geneva, on the prolongation of the MVF in the Jura Mountains, are the Gallo-Romain sanctuaries of Villards d’Héria (Jura, France). The sanctuary provides the ideal archaeological context for studying the cause-and- effect relationship between a faulted bedrock and deformation of archaeological remains. The sanctuaries are spread over two sites (Fig. 2). The upper site, near Lake d’Antre (802 m asl) is bounded by the Antre fault. The lower site, “Pont-des-Arches”, in the Héria Valley (712 m asl) consists of a worship area and bathing facilities. The two sites are connected by karstic conduits (Nouvel et al., 2018), whose flow is driven by a dense fracture network. Excavations have provided evidence of continuous occupation from the first century BCE until the last decades of the third century.