Kraus, R. K.

The aim of this paper is to propose an alternative model for the Pliocene-Quaternary to present evolution of the Northern–Central Apennines by combining geometrical requirements (Riedel shear system) with existing structural and geological geometries (fault systems and their tectonic associations). We define three sectors characterized by different geological, seismological, geodetic and geothermal signatures: the North-Western Sector (NWS), the Western Central Sector (WCS) and the Eastern Central Sector (ECS). According to GPS data derived from literature the three blocks move independently. In particular, the NWS is bound between the ECS/WCS and the Alps; this constraint leads to a stress accumulation responsible for a fragmentation into further several blocks, which move either to the NE or SW. The WCS is relatively stable; the ECS moves towards NE and is characterized by the presence of numerous releasing and restraining bends, which can be related to the action of a main NNW–SSE left-lateral shear zone. Accordingly, the recent and active tectonic setting of the Northern–Central Apennines is rather related to the dynamics of the introduced blocks, caused by the push of the African plate against Europe, than to subduction processes.

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.