Geological and geomorphological observations in relation to the 20 September 1899 Menderes earthquake, western Turkey

The 20 September 1899 Menderes earthquake was the most damaging event that has occurred in the Buyuk Menderes graben in the last 100 years. The earthq uake involved normal faulting along the northern margin of the Buyuk Mender es graben from west of Aydin to Nazilli. A derailed investigation along the northern margin of the graben showed the presence of faults cutting active ly depositing graben Boor deposits in the foot of Neogene hills. Along an E -W trend east of Aydin, a normal fault was located having an observable len gth of at least 3 km and a maximum vertical displacement of about 3.5 m. A stream entering to the graben changed its cause due to this fault. Field ev idence suggests that, in addition to south-side down-throw by as much as 2 m during the 1899 event, there was also at least 1.5 m opening along the su rface break. Field evidence also showed that the 1899 surface break follows a pre-existing break which might have ruptured during the 26 (or 25) BC an d 22 February 1653 events; again south-side down-thrown by at least 1 m and 1.5 m, respectively.