Researches on historical seismicity at Vienna (France): from archaeoseismological observations to the archaeological identification of «Viennese» earthquakes in Antiquity and the Middle Ages
Bruno Helly (1), Alain Rideaud (2), Benoît Helly (3)
(1) Directeur de recherche au CNRS (émérite), Maison de l’Orient
(2) Architecte DPLG, 71100-Tournus
(3) Service Régional de l’Archéologie, DRAC Lyon
In Vienna, Roman city in south-East of France, the observations of archeosismology that we have made revealed a series of disorders, repairs and reconstructions characteristic of ground movements. On the temple of Augustus and Livia already well studied by archaeologists, the first state of Augustan period (around 20 BC) shows rotations, ruptures of alignments, veiling of the wall of the cella. On the Roman forum an arch dated from the end of 1 Century BC presents disorders such as rotations, block displacements and neighbor with an arc whose reconstruction made with re-used materials an partiular technics of vault manifests the aim to obtain a better resistance.
These observations led the archaeologist to reconsider with a more open attention a rich series of archaeological evidence, such as the interpretation of the two states of construction of the Temple of Augustus and Livia, as well as those that we have on the forum, the temporary stop of the construction of large horrea located along the Rhone river, the renovation of the urban plan and the development of the construction of large houses. The archaeologist has also taken over the exploitation of indirect sources of epigraphy and texts: the inscriptions relating to the repair of the aqueducts, the repair of fountains and of a clock, financed by execptional donations from rich citizens.
The research undertaken in association between archaeoseismologists and archaeologist has made it possible the hypothesis that it is most likely an earthquake that caused the almost total destruction of the city, leading to the reconstruction and transformation of monuments and houses. Given the means implemented and the speed of reconstruction after the event, which must date from the end of the reign of Tiberius, the archaeologist proposes to link this reconstruction with the granting of jus italicum to the city by Emperor Caligula in 35 or 36 AD. We sought to extend our observations on medieval constructions. Thus we have noticed disorders and typical reconstructions on the church and the cloister of Saint-André-le-Bas, on the cathedral church of Saint-Maurice and finally on the Château de la Bâtie, built by Jean de Bernin, archbishop Vienna at the end of the 12th Century.
Of the other hand we were able to confront our hypotheses with the observations from the geologists on the existence of a possible zone of tectonic disturbance in the lower valley of a tributary tiver, perhaps caused by an “orphan” fault, which crosses the city just before joining the Rhone valley, We think that the activation of this fault would have occurred three times in historical period, first at the beginning of the Roman imperial era, another time perhaps in the 5 Century AD, if one believes a testimony of Sidoine Apollinaire, and still in the course of the 14 Century AD. On the verification of these hypotheses, once again, archaeologists and archaeoseismologists will try to converge their respective researches.