Of single channel, 70 km, and 900 km of multi-channel seismic reflection data show that Izmir Gulf and surrounding regions are widely deformed by N-S to NE-SW trending active transpressional strike-slip faults, reverse faults and some E-W normal faults. Normal faults are mapped offshore Karaburun-Foqa, in inner part of Izmir Gulf; offshore Alacati-Teke and offshore Kusadasi delimiting the southern scarp of Lesvos basin, Izmir basin, northern scarp of Ikaria basin and continuation of Kucuk Menderes Graben, respectively. Normal faults are cut by strike-slip faults. The major strike-slip faults are the N-S oriented Karaburun reverse fault bordering Izmir Gulf on the west and uplifting the Karaburun Peninsula and the NE-SW oriented strike-slip Tuzla Fault extending from Doganbey Promontory towards Seferihisar ridge onland. This fault pattern can be explained by pure-shear model indicating that the area is under E-W compression, N-S extension, NE-SW and NW-SE strike-slip deformation. Moreover, Tuzla Fault has a regional importance. It separates NE-SW trending structures of the study area from E-W oriented Gediz and Kucuk Menderes grabens and probably continues towards to Iznik at north constituting a transition zone between northern transpressional region and southern extensional region in the western Anatolia-Aegean Sea. (c) 2005 Elsevier B.V. All rights reserved.