The Büyük Menderes Graben is an active rift basin in western Turkey, part of the Western Anatolian Extension Zone. [1] It is about 140 km long and 2.5–14 km wide with a west–east trend. [2] It was formed during the early Miocene and remains active, as shown by historical earthquakes, the largest of which was the M7.5 1653 East Smyrna earthquake. [1] Another event, the 1899 Aydın–Denizli earthquake, also occurred on a fault associated with the graben. [3] The graben forms a rift valley, through which the Büyük Menderes River drains into the Aegean Sea.