Stress tensors with the aid of a large number of fault plane solutions provide important contributions for the evaluation of the seismotectonic setting of a region. In this study, earthquake activity between the dates of 02.09.2006 and 31.03.2011 at Eastern Ganos Offshore and Eastern Tekirdag Basin, which are located on the western branch of the North Anatolian Fault Zone, were analyzed using a current data set of fault plane solutions derived from a very dense seismic network. Earthquakes were selected with the following criteria; minimum local magnitude of 2.0, number of minimum P-wave first motion polarity of 10 and toleration of maximum misfit of 1. During the study 85 and 75 source mechanisms were determined in the Eastern Ganos Offshore and Eastern Tekirdag Basin areas, respectively. Through the determination of 3831 high quality P-wave first motion polarities for the selected 160 earthquakes, the number of average polarity per earthquake was 24. Average error depth, latitude, longitude, and GAP values were also obtained as 2.8 km, 1.1 km, 1.3 km and 62 degree, respectively. Furthermore, using the algorithm of Horiuchi et al., (1995), simultaneous focal mechanism solutions of individual earthquakes and recent stress regimes have been determined for the selected clusters. As a result, it was found out that the NW-SE trending transtensional stress structures leading mostly normal and oblique faulting systems are predominant in the Eastern Tekirdag Basin Cluster. Nevertheless, Eastern Ganos Offshore Cluster was presented as a dextral strike-slip deformation system through the transition from normal to reverse faulting system. Furthermore, 07.06.2012 Marmara Sea (ML5.1) and 25.07.2011 Marmara Sea (ML5.2) Earthquakes were also analyzed. It was stated that the stress tensor solutions obtained using mostly small size earthquakes fit the source mechanisms of these two moderate size earthquakes. Moreover, the orientations of the principal stress axes of the Eastern Tekirdağ Basin area have found close the ones for the Eastern Marmara Region. Consequently, in this research, a new and comprehensive approach to the fault geometries, present stress state, and seismotectonic structures of the Western Marmara Sea Region have been proposed by a detailed analysis of the results of the large number of fault plane solutions of earthquakes using the densest seismic network of Turkey. Earthquake focal mechanisms in the Eastern Ganos Offshore and Eastern Tekirdag Basin areas.