SUBMARINE ACTIVE TECTONISM AND SEISMIC STRATIGRAPHY IN THE GULF OF IZMIT, MARMARA SEA-TURKEY

The North Anatolian Fault (NAF) is an E–W trending right-lateral strike-slip transform fault running across northern Turkey with a length of 1,600 km and accommodates ~23-25 mm/yr of present-day right-lateral motion between the Anatolian and Eurasian plates. The fault zone is one of the most tectonically active regions of the world. The fault passes close to population centers in northern Turkey (e.g., Istanbul), and recent large earthquakes have had disastrous consequences (e.g., the 17 August 1999 7.4 Izmit earthquake). NAF splinters into multiple strands, some of which are submerged under the Marmara Sea.

The Gulf of Izmit is located in the eastern part of Marmara Sea and the northern strand of the NAF enters the Marmara Sea through this gulf. Three connected basins, the western (Darıca), central (Karamursel) and eastern (Golcuk) basins, form the Gulf of Izmit. Multi-channel seismic (MCS) reflection data were acquired with the R/V MTA Sismik-1 along 63 lines totaling 348 km in September 1999, just after the 17 August 1999 earthquake. The seismic data were processed with Focus (5.0) software in data processing laboratory of the Department of Geophysics, Istanbul Technical University with a conventional data processing stream. The seismic stratigraphy and structural observations are made by using the stacked and time migrated seismic sections.

The main branch of the dextral NAF enters the Gulf of Izmit from its eastern part and crosses the gulf mainly in an E–W direction and connects to deep troughs of the Sea of Marmara in the west. The fault causes an active tectonic stratigraphic setting for the Gulf of Izmit and it mainly forms a nearly vertical fault surface from sea bottom to about 1,000 m depth. To the south of the NAF three seismic sequences are classified from the seismic sections. Mapping of these seismic horizons give knowledge for a westward-migrated depocenter in Karamursel basin. The overall average sedimentation rate is 0.4 mm/year according to these three youngest seismo-stratigraphic units.