Investigation of upper mantle structure of marmara and its surrounding regions using teleseismic tomography

The main scope of this research is the investigation of the lithosphere and deeper mantle structure of the Marmara and its surrounding regions . We present highresolution teleseismic tomographic results using the travel time of far-field earthquakes. Investigation of the heterogeneous mantle structure, the delineation of fast seismic velocity anomalies in the mantle, delineation of possible subducted oceanic lithospheric slabs, the identification of mantle upwelling zones can be achived using seismic tomography. In this study, we used 15,624 direct P phase arrival times from 126 earthquakes recorded at a variety of permanent seismic networks (Boğazici University, Kandilli Observatory and Earthquake Research Institute and Disaster and Emergency Management Authority). In order to increase the station coverage and increase the resolution, we selected arrivals from earthquakes with moment magnitude 5.5 and greater (Mw>5.5) at distances between 28° and 90° from the stations for direct P phases (126 earthquakes). After combining data sets, relative arrival time residuals and errors were determined with respect to the ak135 one dimensional global velocity model using the Adaptive Stacking Method. These results were used in the fast marching teleseismic tomography inversion and we have obtained new threedimensional (3-D) P-wave velocity perturbations of the mantle beneath Western Anatolia down to about 700 km depth. The tomographic results show the existence of two distinct high velocity anomalies in the mantle. Seismic tomographic cross-sections clearly show the northward subducting African slab as well as the low-velocity subduction wedge located between this slab and the Aegean continental lithosphere. This low-velocity wedge can be interpreted as the mantle source region of the active Aegean arc volcanism. The obtained tomographic results also indicate the presence of a distinct, southward subducting, high-velocity zone in the north. This high-velocity zone, which is located beneath the Marmara Sea, extends down to 350 km and it consists of two oceanic lithospheric pieces that are detached at about 200 km depth. This high-velocity zone can be interpreted as the remnant of the southward subducting Black Sea oceanic lithosphere. A high velocity zone that would be expected from the İzmir Ankara-Erzincan suture zone was not clearly observed in this study.