Active transpressive surface faulting in north-eastern calabria, southern Italy: early results of geomorphological, stratigraphic and paleoseismological analyses

Abstract

We here first described field evidence of Holocene transpressive faulting in north-eastern Calabria, about 15 km east of Rossano, in the area of Mirto. There, we analysed a stratigraphic sequence exposed along a WNW-ESE trending, 4-km-long scarp, anomalous in the local geomorphic context. The sequence was made of marine deltaic sediments with embedded colluvial deposits, daylighted by an excavation for a building. The excavation occurred on top of a fluvial terrace at ~15 m a.s.l., that was embedded in a MIS 5a marine terrace. Micropaleothological analysis and 14C radiometric dating defined an Early(-Middle) Pleistocene age for the marine sequence and a Holocene age for the overlain colluvial deposits. The whole sequence was back-tilted, warped and offset along shear planes showing an evident reverse sense of motion. The uphill sense of displacement, the local geomorphic setting and the available literature allowed to exclude any other cause (e.g. deep-seated or shallow landsliding, salt diapirism) than tectonics for the observed deformations. By considering the current knowledge about the structural and active tectonic framework of the northern Calabrian Arc, the observed reverse fault planes can be the surface expression of either local active compressional deformations (i.e. restraining bend) along the Rossano-Cirò Marina strike slip shear zone, being part of the regional, left-later strike-slip Pollino Line, or an inland splay of the active transpressional tectonic structures offshore of the Sibari Plain and the Rossano area. Even if at an early stage, our observations can represent a new piece in the active tectonics puzzle of the boundary region between the Calabrian Arc and the southern Apennines. They also provide new hints for seismotectonic evaluations, taking into thorough consideration that the ob-served tectonic features occur in the epicentral area of the 1836 (Mw 6.2) earthquake, the causative fault of which is still debated. Ultimately, the present study raises new questions about reverse surface faulting hazard assessment for this region.