Tectonic Setting of the Eastern Marmara Sea

Abstract

The westward escape of Anatolian plate by dextral strike-slip motion produces large earthquakes along the right-lateral North Anatolian Fault Zone and plays an important role on the tectonic evolution of the Marmara Sea region. On August 17, 1999, a devastating earthquake occurred on the northern strand of the North Anatolian Fault Zone with a Mw=7.4 and struck the eastern Marmara Sea region. The main fault, which was well defined and mapped for 100 km, from Duzce to the east to the Izmit Bay, went offshore at the southeast corner of this bay. Following the earthquake, its extension at sea was investigated by high-resolution shallow seismic survey. In general, the area can be characterised by a negative flower structure controlled by a single master fault, the northern branch of the North Anatolian Fault Zone. The bending of the master fault gives rise to en echelon faults, opening the sub-basins in the Izmit Bay as releasing bend basins. In addition, due to dextral shearing mechanism, many synthetic dextral faults which are oblique at low-angle to the master fault were developed. Short and dextral synthetic faults strike ENE-WSW in the south, while dextral faults (remnants of the Thrace-Eskicehir Fault Zone) strike WNW-ESE in the north. These faults absorbed the deformation at the western end of the fault ruptured during the 17 August 1999 Earthquake.