Transition of the North Anatolian Fault Zone (NAFZ) in the Sea of Marmara

Abstract

The North Anatolian Fault Zone (NAFZ), with a total length of ca. 1500 km, is one of the worlds important active strike-slip fault. It is a seismically active right-lateral transform, which takes up the relative motion between the Anatolian and Eurasian plates. This fault zone became first active in the Late Miocene to Pliocene and its lateral displacement is about 20 mm/year, and it consists along most of its length essentially of a single fault; however it splits first into two branches near Bolu and then into three branches near Adapazan-Izmit region. In order to determine the situation of the NAFZ in the Sea of Marmara some geophysical studies were carried out. Over 1670 km long of airgun seismic and magnetic profiles were run in the Sea of Marmara in 1989, and over 300 km long of seismic profiles in the Bay of Izmit in 1994 with using R/V K. Piri Reis of Dokuz Eylul University (Izmir). As a result of the seismic studies the Sea of Marmara is dissected by two major fault systems. One of the first system consists of E-W striking, transtensional boundary faults and a number of secondary fault system subparallel to them. The second system showing NE-SW trending subvertical strike-slips, and their conjugates oriented NW-SE direction. According to our data all these fault systems segment the deep part of the Sea of Marmara into 5 tectonic blocks. Three of these 5 blocks are interpreted as pull-apart basins characterized by transtension. They are separated by trans-pressional push-up structures. However, the new data obtained from recent studies in the Sea of Marmara are interpreted that the northern branch of the NAF is going mostly as a single dextral strike slip fault system across the Sea of Marmara.