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

摘要

Measurement of a stream offset and cosmogenic dating (10~Be) of the alluvial surface intowhich the stream incised yield a preferred late Holocene slip rate of 18.6 +3.5/-3.3 mm a-1for the central part of the North Anatolian fault (NAF) at TahtakOpru, Turkey; use ofvariable cosmogenic production rate (VPR) models yields a slightly slower rateof 16.4 +6.4/-4.5 mm a~-1. The offset drainage (Karanlik Dere), which flows southwardalmost perpendicular to the east-west trace of the NAF at the site, is displaced right laterally by55 ± 10 m, with no vertical displacement. A 10~Beage of –3 ka (-3.5 ka VPR) from the top of aboulder on the best preserved part of the incised alluvial surface provides the most reliablemaximum age for the onset of incision; 11 The ages from cobbles collected from thecultivated surface to the south yield younger ages, consistent with exhumation, erosion, andmechanical mixing during plowing. Our 18.6 +3.5/-3.3 mm a-1 rate is similar to othergeologic slip rates measured along the NAF, all of which cluster between 15 and 20 mm a-1over a wide range of (103-105) timescales. All of these geological rates, however, are slowerthan the ~25 ±2 mm a I short-term rate of elastic strain accumulation measured geodetically.This disparity suggests the possibility that the NAF is experiencing a strain transient inwhich the lower crust beneath the fault is deforming faster than its long-term rate.