GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.2 191 to seismotectonic issues. Indeed the brittle-ductile transition, though not exactly coinciding with, represents a fair approximation to the seismic-aseismic boundary, which is more precisely related to the velocity weakening-velocity strengthening transition (Tse and Rice 1986; Scholz 1988). During the interseismic period we can, in any case, consider the depth of the brittle- ductile transition (hereinafter BDT) as a reasonable indicator for the maximum depth extent of (seismogenic) faulting. Accordingly, a precise rheological modelling can help distinguishing the brittle, potentially seismogenic layer, also termed schizosphere (after Scholz 1988), from the undelying, ductilely deforming plastosphere . We then decided to apply the rheological modelling to the Aegean Region for a twofold reason: firstly, it represents one of the most seismically active area all over the world, and therefore it allows to compare and validate the rheological results with a totally independent data source, namely well-located seismicity. Secondly, the Aegean Region is characterized by a dense pattern of seismogenic faults, whose terminations at depths are not always well defined and therefore represent ideal candidates for applying the rheological modelling results, in order to help constraining the geometry and the seismogenic potential of such faults, with the final aim of improving their relative seismotectonic characterization. Data and Methods . We realized two rheological transects ( ca. 550 km long each) crosscutting each other, one being parallel to the Hellenides belt axis and the other orthogonal to it (Fig. 1). The latter is therefore WSW-ENE oriented, originates in Corfù (WSW) and terminates in Thrace (ENE), thus encompassing all the structural domains and tectonic nappes which constitute the Hellenic orogen. The former is, on the contrary, parallel to the main structures of the Hellenides belt and lies just to the east of the topographic watershed of the mountain chain, running from Albania/FYROM border to southern Peloponnesus. The rheological modelling has been carried out by realizing closely spaced (mean inter-distance around 10 km) 1D strength profiles and subsequently interpolating them. Yield strength profiles, which display the value of the maximum shear strength (expressed in terms of differential stress) of the rocks as a function of depth, have been produced following a simplified approach, which only takes into account two main rheological behaviours, namely the (brittle) frictional sliding and the (ductile) power-law creep. We decided to discard the semi-brittle rheological behaviours representative of the so called “brittle fracture” (Zang et al ., 2007) or “frictional- viscous” (Bos and Spiers, 2002) rheologies, because of the following reasons. First, since we are mainly interested in the BDT depth and only secondarily in the values of the associated Fig. 1 - Topographic and bathymetric map of the Aegean Region. The blue dots indicate the position of the 1D strength profiles along the WSW-ENE trending transect, purple ones are for the NNW-SSE trending transect.