SLIP RATES ALONG ACTIVE FAULTS ESTIMATED WITH COSMIC-RAY-EXPOSURE DATES - APPLICATION TO THE BOGD FAULT, GOBI-ALTAI, MONGOLIA

Dating morphological features displaced along active faults presents a major difficulty in evaluation of slip rates. We used insitu-produced Be-10 to calculate minimum ages for alluvial surfaces misaligned by m ovement along a major active fault in the Gobi-Altai (western Mongolia ). The maximum slip rate of similar to 1.2 mm/yr suggested by this met hod contrasts strongly with rates of similar to 20 mm/yr that we estim ated by correlation of alluvial deposition with warm humid periods ass ociated with the last glacial termination estimated to have occurred a bout 12 ka in western Tibet. The Be-10-based slip rate indicates that strong earthquakes can occur along faults with low slip rates and demo nstrates the contribution of cosmic-ray-exposure dating in Quaternary tectonic analyses.