PALEOSEISMOLOGY OF THE NORTH ANATOLIAN FAULT, TURKEY: A 2,000 – 2,500 YEAR RECORD OF LARGE, INFREQUENT EARTHQUAKES
HARTLEB, R.D. and DOLAN, J.F., Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, email@example.com, firstname.lastname@example.org
Turkey's long historic earthquake record and the relative mechanical simplicity of the fault system combine to make the central North Anatolian fault (NAF) a model opportunity to study long-term behavior of continental transform faults. We excavated trenches at three sites along the central and eastern NAF. The Cukurcimen site, near Refahiye in north-central Turkey, yielded a complete record of surface ruptures for the past 2,500 years; five events occurred during this time. These are interpreted as: (1) the historic 1939 Mw 7.9 earthquake; (2) the historic 1254 earthquake; (3) the historic 1045 earthquake; (4) an earthquake that probably occurred late in the interval between 250 and 540 A.D., possibly the historic 499 earthquake; and (5) an earthquake that probably occurred sometime between 770 and 200 B.C. The Alayurt site, near Ladik in north-central Turkey, yielded a record of earthquakes for the past 2,000 years; four, and possibly five, events occurred during this time: (1) the historic 1943 Mw 7.7 earthquake; (2) the historic great 1668 earthquake; (3) a late 8th to early 13th c. A.D. event (possibly part of the historic 967 – 1050 sequence that ruptured most of the NAF); (4) a 1st to 3rd c. A.D. event, possibly the historic 236 earthquake; and (5) a possible late 4th to early 11th c. A.D. event. The Ulaslar site, near Gerede, yielded a record of three earthquakes: (1) the historic 1944 Mw 7.5 earthquake; (2) the 1668 earthquake; and (3) an as-yet poorly dated, earlier event. Our findings, when coupled with other published results and the historical record, enable us to construct a preliminary space-time history of earthquakes along the NAF. The most striking aspects of this analysis are: (1) the rarity of earthquakes at any given place along the fault, suggesting that the fault typically ruptures in large, infrequent events; (2) quasiperiodic earthquake occurrence; inter-event times range from approximately 200 to less than 900 years, and vary by a factor of 3 to 4; (3) almost the entire length of the NAF ruptured in short-lived clusters of activity in the 16th to 18th c. and in the 10th to 12th c., similar to the 20th c. sequence; and (4) historical data from the East Anatolian fault (EAF) suggest a temporal anti-correlation of earthquake activity on the NAF and EAF.