Evolution of the middle strand of North Anatolian Fault and shallow seismic investigation of the southeastern Marmara Sea (Gemlik Bay)

The Gemlik Bay is developed as a pull-apart basin during the late Pliocene-early Pleistocene mainly controlled by west-trending dextral strike-slip faults along the middle strand of the North Anatolian Fault zone, with the NW-trending Thrace-Eskişehir Fault playing secondary role. The North Anatolian Fault reached the eastern Marmara Sea ∼3.5 Ma ago, where its middle strand intersected the Thrace-Eskişehir Fault. GPS slip vectors measured on the Armutlu and Mudanya blocks show a displacement of 7-8 km during the last 3.5 Ma. The middle strand of the North Anatolian Fault zone has lower tectonic activity than the northern strand. Because uplift of the southeast Marmara Sea region has been continuous since the late Pliocene, the presence of fluviatile, lacustrine and deltaic environments in the Gemlik pull-apart basin over the same period supports a lower lever of tectonic activity. The transgressive Marmara Formation was deposited on top of these fluvio-lacustrine deposits following the Mediterranean inundation at ∼600 ka via the Strait of Çanakkale. The Gemlik basin was affected both by two major sea-level falls at 160-132 and 24-11 ka, and minor short-lived sea-level variations, as a result of becoming a lacustrine setting five times since ∼600 ka. During these lowstands, stacked delta successions were deposited around the lake and on the transgressed shelves of the Marmara Sea.