GNGTS 2014 - Atti del 33° Convegno Nazionale

Calabria, shows a completely different structure (Fig. 2b), with a more elevated accretionary wedge, 500-600 m shallower than in the western region, characterized by steeper topographic slopes and higher deformation rates. The two lobes are delimited by a NW-SE deformation zone (Fig. 3) crossing the entire subduction complex from the abyssal plain to the Messina Straits. This newly proposed structure, might represent the shallow expression of different stages of subduction and plate fragmentation in the Ionian Sea, and reflects a recent phase of plate re-organization in the central Mediterranean. In particular, it bounds sectors of the WL where the slab is already detached, and regions in the EL where local earthquake tomographic maps image a continuous slab penetrating into the mantle (Neri et al. , 2009). Along this tectonic boundary the WL is down-dropped relative to the EL. Margin segmentation occurs along a second NNW-SSE trending crustal discontinuity running from the Alfeo seamount to the Etna volcano and already described by many authors (Nicolich et al. , 2000; Chamot-Rooke et al. , 2005; Del Ben et al. , 2008; Argnani and Bonazzi, 2005; Polonia et al. , 2011, 2012; Gallais et al. , 2013) and described as related to deeply rooted processes (Govers and Wortel, 2005; Rosembaum et al. , 2007). We propose that margin segmentation reflects a recent plate boundary re-organization in the Ionian Sea, connecting the compressive belt in northern Sicily to the Hellenic Arc system and dissecting the CA subduction complex. ���� �������������� �� �� ��������� ���� �������� ���� This reconstruction is in agreement with geodetic data and earthquake slip vectors observations which suggest the existence of a microplate in the central Mediterranean. The discontinuity between the two lobes would thus represent a major component of the southwestern (hitherto poorly constrained) boundary of this microplate. The motion of Africa relative to Eurasia would be accommodated along this structure by relative rotations between the different blocks resulting from African plate fragmentation. Active faults offshore the Messina Straits and seismic hazard. If, on one hand, it is well known that the Messina Straits region is the locus of active deformation and destructive Fig. 3 – Tectonic map of the westernCAareawithmajor seismogenetic structures indicated (STEP, Splay -1, -2, -3, and Messina Straits fault systems). Filled circles mark earthquake epicenters in the region during the period 1981- 2011. Radius of the circles is proportional to estimated magnitude (from 1.2 to 5.9), while colors represent depth intervals (from 0 to 50 km; black > 50 km). The directions of maximum and minimum horizontal contractional strain rates described are represented in three key sites of the western CA (black and white arrows): they are in agreement with the proposed seismogenic fault systems. Modified from Polonia et al. (2012). 166 GNGTS 2014 S essione 1.2