A late Holocene slip rate for the central North Anatolian fault, at Tahtakopru, Turkey, from cosmogenic 10Be geochronology: Implications for fault loading and strain release rates

Measurement of a stream offset and cosmogenic dating (Be-10) of the alluvial surface into which the stream incised yield a preferred late Holocene slip rate of 18.6 + 3.5/-3.3 mm a(-1) for the central part of the North Anatolian fault (NAF) at Tahtakopru, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of similar to 16.4 + 6.4/-4.5 mm a(-1). The offset drainage (Karanlik Dere), which flows southward almost perpendicular to the east-west trace of the NAF at the site, is displaced right laterally by 55 +/- 10m, with no vertical displacement. A Be-10 age of similar to 3ka (similar to 3.5 ka VPR) from the top of a boulder on the best preserved part of the incised alluvial surface provides the most reliable maximum age for the onset of incision; 11 Be-10 ages from cobbles collected from the cultivated surface to the south yield younger ages, consistent with exhumation, erosion, and mechanical mixing during plowing. Our 18.6 + 3.5/-3.3 mm a(-1) rate is similar to other geologic slip rates measured along the NAF, all of which cluster between 15 and 20 mm a(-1) over a wide range of (10(3)-10(5)) timescales. All of these geological rates, however, are slower than the similar to 25 +/- 2 mm a(-1) short-term rate of elastic strain accumulation measured geodetically. This disparity suggests the possibility that the NAF is experiencing a strain transient in which the lower crust beneath the fault is deforming faster than its long-term rate.