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 earthquake involved normal faulting along the northern margin of the Buyuk Menderes graben from west of Aydin to Nazilli. A detailed investigation along the northern margin of the graben showed the presence of faults cutting actively depositing graben floor deposits in the foot of Neogene hills. Along an E-W trend east of Aydin, a normal fault was located having an observable length 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 evidence 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 surface 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 and 22 February 1653 events: again south-side down-thrown by at least 1 m and 1.5 m, respectively. Keywords: Turkey, Holocene, faulting, earthquake, geomorphology.