Determination of Upper Mantle Heterogeneity Beneath Aegean-Anatolian Region from Travel Time Tomography

Movement and the deformation of the continental lithosphere are not clear completely. In the first end-member model, the lithosphere consists of essentially rigid blocks (with most of the strength located in the upper crust) that float on the asthenosphere, are separated by lithospheric faults, and move because of forces applied to their edges. The second model holds that the lithosphere (including the upper mantle) deforms as a continuum, and that the upper crust moves in response to tractions applied to its base. Most elements of the debate are related to deformation at the surface or within the shallow crust (fault kinematics, geodetic displacements, or earthquake mechanisms). The Aegean Sea, the surrounding Greek coasts and the western Turkey, along with the Hellenic Arc, are the most active seismic areas of the Mediterranean Basin and of the whole Alpine-Himalayan chain. The catalogues of seismicity are certainly incomplete for low magnitude events (M<4.5), but the map permits to identify the active seismogenic zones in a broad scale. Several earthquakes with magnitudes greater than 6 occurred during the instrumental period. The seismicity distribution shown in Figure 1 and the trend of the focal mechanisms in Figure 1 are related to the major tectonic features. The earthquake depths are generally normal (<15 km), with exception for the subduction zones where the events occur at intermediate and high depths (>30 km). This happens along the Hellenic Arc and in the Antalya Gulf (southern Turkey). In the whole area, the frequency of events with magnitude greater than 4, is evident, but there are many events with lower magnitudes. Teleseismic tomography is a powerful tool used to obtain about the deep velocity perturbations in the Earth, using travel times recorded by a regional network from distant sources (usually at distances of more than 20°). This method has been developed since the seventies [1] and has been successfully used for the investigation of different regions (e.g. [2-5]). The images of seismic anomalies are then used for the estimation of the distribution of temperature, density and other parameters [6], which then can be used for geodynamic modeling, gravity inversion [2,7] and other applications. We expect to obtain a 3D image of the velocity structure of the Hellenic Arc Zone beneath Greece and Aegean region to a depth of about 300 km. The results might provide better constrains on the evolution of the slab beneath Anatolia and the Aegean. We will compare our results with previous works and regional data.