A 3D rheological model for the Aegean Region: Mechanical layering and seismotectonic implications

We implemented a 3D thermo-rheological model for the broader Aegean Region, with special focus on determining the depth of the brittle-ductile transition (BDT) and the thickness of the brittle, potentially-seismogenic layers. In order to gain a more precise and comprehensive view on the thermo-physical characteristic of the main rheological transition, the model provides strength and temperature distribution along depth, as well as the relative values at the BDT depth. In particular, the reconstruction of a 3D model, allows to identify major trends and peculiarities, and to characterize the BDT depth, temperature and strength variations within this sector of the Mediterranean realm. The results indicate that a shallow transition (10–15 km) is common in the internal Aegean Region and most of continental Greece, while the external regions geodynamically associated to the Hellenic subduction show much deeper BDTs (around 30–35 and 40–45 km in continental and oceanic lithosphere sectors, respectively). The numerical modelling factors appearing to exert the greatest control on the BDT depth, and more in general on the spatial distribution of the rheological properties, at the scale of the whole study area, are the surface heat flow (as a proxy for the geothermal gradient) and the nature of the considered crust (continental vs oceanic). As a direct application of the results, the reconstructed 3D model of the shallower BDT is then exploited within the Aegean Region for defining the thickness of the seismogenic layer and its lateral variations. This in turn allows to independently constrain the maximum width of GreDaSS seismogenic sources and, by applying empirical relationships, to better quantify the maximum magnitudes expected on these sources.