Strike-slip geometry inferred from the seismicity of the Northern-Central Apennines (Italy)

The aim of this paper is to draw attention to the real number and distribution of strike-slip earthquake focal mechanisms that are displayed in the recent seismicity of the Northern-Central Apennines. Their relation to the superficial normal fault plane solutions and thrust front along the Eastern side of the Apenninic chain can be described by a geometrical model (Riedel-System, also Riedel shear model). First we define three sectors characterized by their different seismological signatures: the North-Western Sector (NWS), the Western Central Sector (WCS) and the Eastern Central Sector (ECS). These three blocks, according to the available data, act independently from each other as a consequence of interaction among themselves, the forces induced by plate tectonics in the Mediterranean area and the blocking effect of the Alpine Chain, leading to an increased amount of transpressional, pure strike-slip and transtensional tectonics below 10 km depth.

► Seismicity hints three sectors with different seismotectonic characteristics.
► Focal mechanisms indicate prevalence of transpressive and transtensive regimes.
► Riedel shear system validates the evidences therefore it is proposed as an alternative geometrical model.