Le problème de l'activité des failles de Nîmes, de Salon-Cavaillon et de la moyenne Durance (SE de la France) : apports de la géomorphologie structurale/The problem of tectonic activity along the Nîmes, Salon-Cavaillon and moyenne Durance fault zones: evidence from structural geomorphology

Abstract

Abstract The tectonic activity along the main faults of western Provence is studied by the means of structural geomorphology. This activity is demonstrated by seismotectonic analysis in the western Provence and lower Rhône regions. Mainly focused on the Moyenne Durance, Salon-Cavaillon and Nîmes fault zones and along a few compressive zones, it follows a complex tectonic history which has interfered all along the Cenozoic times with alternate stages of erosion, planation, sedimentary infilling of basins and incision. Together with the low rates of recent tectonism, this history explains why the geomorphic indices of activity along the fault zones are faint or ambiguous. Medium (hectometric to kilometric) scale landforms are the only geomorphic features that can be used for the purpose of tectonic analysis, but they result from a longer tectonic history than the short period of activity revealed by seismic and palaeoseismic analysis. Their study does not show any significant post-Pliocene activity along the Nîmes fault, suggests only a moderate and poorly characterized post-Pliocene activity along the Moyenne Durance fault zone, and may indicate some post- Miocene normal or strike-slip movements along parts of the Salon-Cavaillon fault zone, with a weak subsidence west of it (Carpentras basin). These results are in fairly close agreement with those of geodetic and seismic studies. Therefore, structural geomorphology is useful for validating geophysical and geological interpretations of tectonic movements in weakly active zones, particularly by giving upper limits to the amplitude of cumulate movements during given periods.