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

摘要

Measurement of a stream offset and cosmogenic dating (10Be) 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 Tahtak?prü, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of ～16.4 +6.4/?4.5 mm a?1. The offset drainage (Karanl?k Dere), which flows southward almost perpendicular to the east-west trace of the NAF at the site, is displaced right laterally by 55 ± 10 m, with no vertical displacement. A 10Be age of ～3 ka (～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 10Be 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 (103–105) timescales. All of these geological rates, however, are slower than the ～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.