Abstract: The NW-trending Datça Graben, E-W trending Reşadiye Horst, Gökova and Hisarönü Grabens are the mostimportant morphologic and structural units ofthe SouthwestAnatolia on which, tectonic evolution was controlledby NW-SE, NE-SW and E-W trending faults. The Datça Graben has been started to develop as a halfgraben on theLycean Nappes ofthe central part ofthe Reşadiye Peninsula under the control ofNW-trending southern marginalfault during early Pliocene. Lagoonal-fluvial environment connected with shallow marine has evolved itsevolution as a graben till late Pliocene (late Piacenzian). E-W trending Gökova Graben and Hisarönü Graben,started to develop under the effect of N-S directed extension, ends the development of the Datça Graben. TheGökova Graben is about 140 km long and enlarges from about 5 km to 30 km westward, and activeYali andNisyrosvolcanic centers are located at the western tip ofthe peninsula. E-W trending southern marginal faults of thisgraben and northern marginal faults of the Hisarönü Graben cut the late Pliocene deposits of Datça Graben,forming Reşadiye Horst between these two grabens. This is an important evidence for the development ofGökovaand Hisarönü Grabensstarting from early Quaternary.This region is one of the seismically active regions of the southeast Aegean Sea. The records of historic andinstrumental period shows the presence ofthe strong earthquakes with magnitudes of7.7 (Ms) and intensity ofX,and the effect of important tsunamies in the region. Based on the focal depth and fault plane solutions of theearthquakes (MsS4) occurred in the region between 2000-2006, it is observed that shallow earthquakes associatewith E-W trending normal fault planes, where as the deep earthquakes associate with oblique to strike-slip faultplanes. The concentration of earthquake epicenters in the central and northern part of Gulf of Gökova is animportant evidence for the seismic activity of the central part and northern margin of the Gökova Graben.However, the increase in the density ofdeep focused earthquakes at the south and SW ofReşadiye Peninsula mustbe related with northward subduction along theAegean trench. Based on the earthquakes ofthe historic period andseismic activity ofthe region, we can conclude that the seismic risk and tsunami probability ofthe region is stillvery high.