Structural and stratigraphical data reveal that the basin was initially formed as a lacustrine basin bounded by a volcanic ridge from the west; it was subsequently uplifted and deformed probably as a result of Pliocene wrench-dominated strike-slip tectonics, which is characterised by NNW-SSE horizontal ¦Ò3 and vertical ¦Ò2. Post-Miocene strike-slip faulting along the ?BTZ occurred along a right-lateral shear zone in the Manisa Basin. This suggests that some branches of the right-lateral movement of the North Anatolian Fault Zone may continue into the WAEP. The youngest stage shows an extension-dominated transtension with a NE-SW trending ¦Ò3 and a vertical ¦Ò1. These results are consistent with progressive deformation developed during late Pliocene and onwards wherein the axis of minimum horizontal stress remained in the horizontal plane but the intermediate and maximum horizontal stress axes switched position in the vertical plane. In addition, available palaeostress data for the Gediz Graben are consistent with the pure extension in the eastern and middle part of the graben and with the wrench-to-extension-dominated transtension in the western part, where the Manisa Basin is located. This indicates a NE-SW trending segment boundary zone forming the western end of the E-W trending Gediz Graben.