Structure of the Marmara Sea Basin in the North Anatolian Fault Zone

Abstract

The Marmara Sea basin should be considered to form part of the North Anatolian Fault (NAF) and the Aegean crustal regime in which a listric-faulted upper crustal section overlies a lower crust that was thinned in a ductile manner, the overall crustal thickness being about 25-30 km. The local Moho upbulge of about 5 km is consistent with Bouguer gravity anomalies as shown by modelling. As the North Aegean area, the Sea of Marmara is undergoing a combination of right-lateral strike-slip and north-south extension with the formation of pull-apart basins. As a result of the collision of the Arabian and Anatolian land masses during the Middle Miocene, the westward escape of the Anatolian block gave rise to E-W compression in western Turkey, the relief of which was produced by N-S extension. In northern Turkey and towards the North Aegean Sea: the NAF splits into several fault strands defining a broad tectonic zone with associated high swarmlike seismic activity. The Marmara Sea basin is the extension of the Thrace basin in the north and northwest. During the Middle Eocene, the subsidence of basement occurred, creating the Thrace basin. Therefore it could be assumed that the extensional basins of the Sea of Marmara have existed since the Eocene. According to interpretation of geological, geomorphological and geophysical data, the Sea of Marmara can be divided into five different blocks which are controlled by two sets of fault systems: (i) almost E-W trending normal faults (the Northern and Southern Boundary faults); and (ii) NE-SW oriented subvertical strike-slips. The blocks are undergoing relative vertical motions and rotations. The Marmara Sea basin accommodates strike-slip and extensional movements. The east-west trending normal fault systems of the Sea of Marmara is a diffuse zone of crustal thinning associated with an estimated 30 percent of north-south extension since the Tortonian.