HR: 1340h
AN: G53A-0869    [Abstracts]
TI: A 2000-year geologic slip-rate for the North Anatolian fault using cosmogenic ³⁶Cl dating
AU: * Kozaci, O
EM: kozaci@usc.edu
AF: University of Southern California, Department of Earth Sciences, ZHS 117, Los Angeles, CA 90089-0740 United States
AU: Dolan, J F
EM: dolan@usc.edu
AF: University of Southern California, Department of Earth Sciences, ZHS 117, Los Angeles, CA 90089-0740 United States
AU: Finkel, R
EM: finkel1@llnl.gov
AF: Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry, Livermore, CA 94550 United States
AU: Hartleb, R D
EM: hartleb@lettis.com
AF: University of Southern California, Department of Earth Sciences, ZHS 117, Los Angeles, CA 90089-0740 United States
AU: Hartleb, R D
EM: hartleb@lettis.com
AF: current address: WLA, 25050 Avenue Kearney, Suite 108, Valencia, CA 91355 United States
AU: Gurcan, M
EM: gurcan@iu.tr
AF: Istanbul University, Department of Geology, Istanbul, 1 Turkey
AB: Understanding the temporal and spatial distribution of strain storage and release on major faults is a key aspect of modern geodynamics. Over the past 15 years GPS measurements have provided increasingly detailed velocity fields along numerous plate boundaries. In contrast, in many locations too few intermediate- and long-term geologic fault slip rates exist to allow for meaningful comparisons between long- and short-term rates. We are using cosmogenic radionuclide dating of offset geomorphic features to generate slip rates for the North Anatolian fault (NAF) in Turkey at a range of time scales ranging from <2,000 to >10,000 years. One of our primary study sites is located along the central part of the fault near the village of Eksik. At the site several major south-flowing drainages have incised >30 m into a well-developed fluvial terrace. These terraces have been offset right-laterally by the east-west fault, which is manifested as a very simple, narrow zone across the study site. The terrace deposits consist almost entirely of distinctive, white limestone cobbles that contrast markedly with the underlying dark grayish-green bedrock. The inner edge of the fluvial terrace is geomorphically well defined over most of the site, facilitating mapping of the fault offset. In addition, the inner edge of the distinctive terrace gravels is exposed in 3D in several natural side drainages. We also excavated three trenches to expose the terrace inner edge adjacent to the narrow fault zone. These exposures and our geomorphic mapping demonstrate that the inner edge of the fluvial terrace is offset by 50 m across the NAF. The age of the terrace is constrained by ten ³⁶Cl cosmogenic radionuclide dates, which yield an age of 2ka. These data indicate a slip rate for the NAF over the past 2,000 years of 24.5+6/-4 mm/yr. This rate is indistinguishable from geodetic (GPS) rates of elastic strain storage across the fault, suggesting that strain storage and release have been relatively constant across the NAF, at least over the past 2 ka. Our ongoing studies of the NAF include sites with larger offsets, which should provide longer-term records of slip rate along the NAF. These longer-term rates will, in turn, allow us to assess the degree to which strain storage and release have been constant (or non-constant) throughout the Holocene.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 7205 Continental crust (1219)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005