Paleoseismological Findings on the Ortakoy-Susehri Segment of the 1939 Erzincan Earthquake Surface Rupture, North Anatolian Fault Zone

The study area is located within the Susehri-Golova basin on eastern part of the North Anatolian Fault Zone (NAFZ). Great devastating earthquakes have been occurred on this highly active seismic fault zone in near historical period. The last great earthquake causing loss of many life and properties was occurred on 27 December 1939 in Erzincan along the eastern part of the NAFZ. This earthquake has created hundreds of kilometers surface rupture, and can also be traced in the study area. Significant information is obtained by early paleoseismological studies carried out especially on the middle and western parts of the NAFZ proving important data about earthquake return periods and magnitudes of seismic activity in the period. Paleoseismological studies on eastern part of the NAFZ are less than western part of the NAFZ. In this study, three trenches were excavated on the 1939 Erzincan earthquake surface rupture. These trenches are located from west to east, in Eskibag, Asagiyenikoy and Asagitepecik villages. Eskibag trench was excavated on a sag pond to the southeast of Sevindik and northeast of Eskibag villages. Asagi Tepecik trench was excavated on the same lineament to the northeast of Asagiyenikoy where a clear fault morphology is observed. The Asagi Tepecik was excavated 2.5 km southeast of the Lake Sut. These trench data are significant because of showing data of large earthquakes repeated during Holocene times. Beside the fact that 1939 surface rupture was observed, the earthquake ruptures formed before 1939 were also observed on trench logs. It is showed that 1939 earthquake surface rupture follows older ruptures and reveals the existence of several different seismic activities prior to 1939 earthquake.