Strain localization in the Sea of Marmara: Propagation of the North Anatolian Fault in a now inactive pull‐apart

Abstract

The Sea of Marmara is presently the site of pure dextral strike‐slip faulting that connects the Izmit Fault in the east to the Ganos Fault in the west along a linear strike‐slip fault that is part of the northwestern branch of the North Anatolian Fault. This active Main Marmara Fault (MMF) cuts across a succession of depocenters and highs. Analysis of a large data set that includes multichannel seismic lines, sparker and deep towed high definition seismics, shows that most of the N120°E trending normal faults framing these depocenters are now inactive as they are sealed by an average thickness of 300 m of sediments. The highs correspond to a series of NE‐SW trending anticlines and reverse faults blanketed by a thin cover of undeformed sediments. We interpret these structures as inverted former transfer faults of the now inactive Sea of Marmara pull‐apart system. Depocenters and highs are the relicts of a former pull‐apart basins and transfer faults system that accommodated the North Anatolian Fault motion within the Sea of Marmara prior to the formation of the MMF. We propose that a relatively short (a few hundreds of thousands of years) period of basin inversion accompanied the localization of strain along the present Main Marmara Fault, until it was fully formed, 200 ± 100 Kyr ago. The preexisting pull‐apart basin system accounts for about 30 km of motion along this fault system and thus probably appeared sometime in late Pliocene or early Pleistocene as a reactivated portion of the old Thrace basin. During the Plio‐Quaternary the Sea of Marmara has been the site of progressive localization of strain.