2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 8
Presentation Time: 3:40 PM

Late Holocene Slip Rate for the North Anatolian Fault, Turkey, from Cosmogenic 10Be Geochronology: Implications for the Constancy of Fault Loading and Strain Release Rates


ABSTRACT WITHDRAWN

, kozaci@usc.edu

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 19 ± 3.5 mm yr-1 for the central part of the North Anatolian fault at Tahtaköprü, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of ~16.5 ± 4.5 mm yr-1. The offset drainage (Karanlık Dere), which flows southward almost perpendicular to the east-west trace of the NAF at the site, is displaced right-laterally by 57.5 ± 7.5 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; eleven 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 19 ± 3.5 mm yr-1 rate is similar to other geologic slip rates measured along the NAF, all of which cluster between 15-20 mm yr-1 over a wide range of (103-105) time scales. All of these geological rates, however, are slower than the 25 ± 1 mm yr-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, possibly in response to long-lived effects of the 20th century sequence of large magnitude NAF earthquakes.