The Buyuk Menderes Graben is a depression in the Menderes core complex of western Turkey. The region is one of the most rapidly deforming regions of continental crust in the world and has exceptionally high seismic activity. In this study, shallow and deep seismic studies were conducted at the Buyuk Menderes graben. These studies included surface geological mapping and two seismic reflection sections. Detailed modelling was performed with the seismic study. In addition to these, a moving windows power spectrum was applied to the Bouguer gravity profile data of the study area. Since no deep well is available in this area, the geological interpretation of the seismic stratigraphy is based on the correlation with the surface geology, this was combined with the major reflections and the seismic facies observed along the profiles, and, thus, four main seismic units can be distinguished in the basin fill. Structural features of the basin is driven by a complex extensional faults system, consisting of a low-angle, S-dipping Buyuk Menderes detachment and by its synthetic and antithetic splays, bordering the opposite flanks of the basin. As a result of conventional deep seismic reflection sections and gravity data, three layers were defined in the study area. The first layer occurs at a thickness of 6 km, and the second layer is between 13 and 18 km. The third layer is at similar to 33 km and may also emphasize Moho depth. The Buyuk Menderes graben has three clear reflectors which are base sediments, brittle-ductile transition, Moho and faults that show a half-graben floored by a detachment. The Moho depth is comparable with previous estimates. According to the results obtained, Bouguer gravity and seismic results are very much consistent with each other. It was observed that at the depths determined from seismic and gravity data, the distribution percentage of earthquake focal depths also rises.