New Chirp seismic data collected from the northern margin of the Marmara Sea in June 2015 and previous Sparker seismic profiles recorded. in 1999 suggest a change in tectonic regime in Messinian. New tectonic lineaments and fault segments were detected at offshore the cekmece lagoons region that is located on one of the possible water corridors with the Paratethys. The faults only affect the older seismic unit (U1), which can be best outlined on the Chirp data. The E-W trending fault offshore Avcilar (OAF) borders the northern edge of a tightly folded sedimentary zone. The NNE-SSW trending fault, namely the Buyukcekmece Fault (BF), passing through the Buyukcekmece Bay, follows a buried valley. Its evolution must be related to the development of the Early Miocene - Early Pliocene Thrace-Eskisehir fault zone (TEFZ). BF and OAF indicate old tectonic activities. in the region, which continued to the North Anatolian fault becoming the most dominant tectonic element in the region. The tappet surface of the stratigraphic unit U1 and its terraces define the thickness of younger deposits (U2), which is thinner in the middle of the shelf. The morphology of the tightly folded zone controls those terraces, which correspond to the Bakirkoy Formation and Kirac member on land. The topmost parts of the terraces must have been eroded during sea level low-stands and cutting of the paleo-valleys. There is no evidence of any tectonic deformation or active fault in the younger seismic unit (U2).