THE SEGMENT STRUCTURE OF SOUTHERN BRANCH OF THE NORTH ANATOLIAN FAULT AND PALEOSEISMOLOGICAL BEHAVIOUR OF THE GEMLİK FAULT, NW ANATOLIA

The North Anatolian Fault (NAF), which is an intra-continental transform fault, is divided into two branches as Northern and Southern branches in Marmara Region. The southern branch which separates from each other by rightward stepovers between Bandırma and Dokurcun valley is formed by three main fault segments as Geyve, İznik and Gemlik from East to West. The length of fault segments ranges between 40 and 57 km and GPS data in Southern branch propose a 5 mm/year slip rate. Two surface faulting events were observed during paleoseismological excavations which had been carried out on 40 km long Gemlik segment and these can be correlated with earthquakes that occurred in 1857 and 1419. The recurrence interval between the last two earthquakes in Gemlik Fault is 438 years. Findings indicate that Gemlik fault was also included into surface faulting of the earthquake in 1419 which its presence is known in İznik fault. At least 95 km long multi-segment surface faulting developed in this earthquake. Based on 5 mm/years slip rate, the cumulative offset amount slip rate of NAF was approximately estimated as 3 meters in 595 years in region between İznik Lake and Dokurcun Valley. Accordingly; it can be stated that the southern branch of the North Anatolian Fault has a potential to trigger a large earthquake as well as the Northern branch.