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Paleoseismologic evidence for the relatively regular recurrence of infrequent, large-magnitude earthquakes on the eastern North Anatolian fault at Yaylabeli, Turkey

Paleoseismologic trenches excavated across the eastern part of the North Anatolian fault at Yaylabeli, Turkey, provide evidence for five surface ruptures during the last 2000 yr. We interpret these events as: (1) the historical 1939 M w 7.9 earthquake; (2) the historical 1254 A.D. earthquake; (3) the historical 1045 A.D. earthquake; (4) an earthquake that occurred between 660 A.D. and 1020 A.D., most probably between 717 A.D. and 844 A.D.; and (5) an earthquake that occurred between 302 A.D. and 724 A.D., possibly the historical 499 A.D. event. Although one of the interevent intervals we document is 685 yr long (between the 1254 A.D. and 1939 A.D. earthquakes), the other three intervals are between 200 and 350 yr long. Our results, which facilitate a rare opportunity to test the completeness of the paleoseismologic record at multiple sites, are generally similar to those from the nearby Cukurcimen trench site, located 2 km to the east, demonstrating reproducibility of the paleoearthquake record. However, the eighth- to ninth-century event (E4) that we document at Yaylabeli was not observed at Cukurcimen. The addition of this event facilitates the recognition of a previously unnoticed North Anatolian fault earthquake cluster, during which at least the eastern and central parts of the fault appear to have ruptured during a brief sequence in the eighth and ninth centuries. Addition of this possible cluster suggests that the North Anatolian fault commonly ruptures in brief, systemwide sequences, although the individual earthquakes in each sequence differ from cluster to cluster in terms of location, magnitude, and rupture sequence. These paleoearthquake data reinforce the idea of relatively regular recurrence of infrequent, large-magnitude earthquakes on the eastern section of the North Anatolian fault. We attribute this relatively simple behavior to the structural maturity of the North Anatolian fault and its relative isolation from other major seismic sources within the Anatolia-Eurasia plate boundary.