Fluvial terrace riser degradation and determination of slip rates on strike-slip faults: An example from the Kunlun fault, China

The use of displaced fluvial terrace risers to determine slip rates along strike-slip faults depends on knowing when risers become passive markers. Typically, chronologic constraints from terrace deposits only place bounds on this age; consequent slip rates may be highly uncertain. Along the Kunlun fault, in northeastern Tibet, we demonstrate that consideration of riser degradation can augment terrace chronology and improve the precision of slip-rate estimates. Multiple offset risers and C-14 age determinations from terrace treads yield a narrow range of slip rates of 4.5 +/- 0.5 m/kyr at one site, but permit a wide range of allowable rates (3 - 10 m/kyr) in an adjacent drainage. Using a locally calibrated sediment transport rate of 3.2-5.4 m(2)/ka, we show that riser morphology at this latter site is consistent with degradation since abandonment of the upper terrace tread. Our analysis indicates that slip rates at this site are similar to 5 +/- 2 m/kyr.