Palaeoearthquakes on the Kelkit Valley Segment of the North Anatolian Fault, Turkey: Implications for the Surface Rupture of the Historical 17 August 1668 Anatolian Earthquake

The 26 December 1939 Erzincan (M-s = 7.8) and 20 December 1942 Erbaa-Niksar (M-s = 7.1) earthquakes created a total surface rupture more than 400 km between Erzincan and Erbaa on the middle to eastern sections of the North Anatolian Fault. These two faulting events are separated by a 10-km-wide releasing stepover, which acted like a seismic barrier in the 20(th) century. To understand the rupture behaviour in this structurally complex section of the North Anatolian Fault, we undertook palaeoseismological trench investigations on the Kelkit Valley segment where there is little or no palaeoseismic information. We found evidence for three surface faulting earthquakes predating the 1939 event during the past millennium in trenches excavated in Resadiye and Umurca. In addition to the 1939 Erzincan earthquake, prior surface ruptures are attributed to the 17 August 1668, A.D. 1254 and A.D. 1045 events. Surface rupture of the 17 August 1668 Anatolian earthquake was previously reported in palaeoseismological studies, performed on the 1944, 1943, and 1942 earthquake fault segments. We suggest that the surface rupture of this catastrophic event jumped the 10-km-wide releasing stepover in Niksar and continued eastward to near Koyulhisar. The existence of different amount of off sets in field boundaries (sets of 4 m, 6.5 m, and 10.8 m) was interpreted as the result of multiple events, in which the 1939, 1668, and 1254 surface ruptures have about 4, 2.5, and 4 metres of horizontal coseismic slip on the Kelkit Valley segment of the North Anatolian Fault, respectively.