The North Anatolian transform fault: its age, offset and tectonic significance

The North Anatolian transform fault is a morphologically distinct and seismically active strike-slip fault which extends for about 1200 km from Karliova to the Gulf of Saros along the Black Sea mountains of N. Anatolia. It takes up the relative motion between the Black Sea and the Anatolian plates, thereby connecting the E. Anatolian convergent zone with the Hellenic Trench through the complex plate boundary zone of the Aegean. For most of its length, the transform has a typical strike-slip fault zone morphology, characterized by narrow ‘rift zone,’ offset, captured and dammed streams, sag ponds and other deformed morphological features. The fault zone is a broad region of extensively crushed country rock cut by a number of parallel and/or anastomosing strike-slip faults. The transform has periods of seismic activity the last of which, from 1939 to the present, is characterized by frequent 6 ≤ M≤7earthquakes; these are separated by quiet periods of about 150 years. The crust along the fault zone is thinner than normal. The transform probably originated some time between the Burdigalian and the Pliocene and has an offset of about 85 km. Whether the offset of the fault changes systematically along its strike is not known. The North Anatolian transform fault seems to have originated as a consequence of the Arabia-Anatolia collision durmg the late (?middle) Miocene, when the Anatolian Plate originated and was wedged out into the oceanic tract of the E. Mediterranean from the converging jaws of Arabia and Eurasia to prevent excessive crustal thickening in E. Anatolia. The westerly motion of Anatolia with respect to Eurasia and Africa caused a great change in the tectonic evolution of the eastern Mediterranean, giving rise to the Aegean extensional regime and to internal deformation of Anatolia.