Abstract: İzmir Bay, one of the recent structures of Westen Anatolia, is a marine basin controlled by NE, NW, N-Sand E-W trending active faults. The southern sector of the bay is bounded by the Izmir Fault, lying between Konak and Güzelbahçe village. The zmir Fault in this section is made up of two mainsegments trending approximately in an E-W direction, and is mapped on a 1/25000 scale from Balçova to Güzelbahçe Village. According to field studies, the İzmir Fault is an oblique-slip normal fault dippingto the north. The northern sector of the bay between Bayraklı and Karşıyaka districts is bounded by the Karşıyaka Fault, which is antithetic to the zmir Fault. In this section, the Karşıyaka Fault ischaracterised by an oblique-slip normal fault dipping to the North.The Seferihisar Fault, which is approximately developed and normal to the Izmir Fault, and hasbeen mapped from Sığacık Bay to Güzelbahçe-Yelki district, forms the eastern margin of the Urla basin.The segment of the Seferihisar Fault that lies between Sığacık Bay and Yelki Village is in the form of aN20E trending right-lateral strike-slip fault. The 5 km length of the fault segment lying between Yelkiand Güzelbahçe trends in a N50E direction and, beginning from Güzelbahçe village, is transformed in the zmir Fault toward the northeast. Within the excavated trenches on the fault segments mapped on a1/1000 scale, it is established that the strike-slip fault (Seferihisar Fault) is transformed by bending in the normal fault (the zmir Fault).Kinematic analysis carried out at 9 stations suggest that the paleostress forming the faults hascontrolled under an approximately N-S extensional direction associated with an E-W contraction. The data support that the kinematically linked Izmir Fault, Seferihisar Fault and Karşıyaka Fault contributed to the opening of Izmir Bay as a response to the transtensional forces.