THERMOLUMINESCENCE DATING OF FAULT-SCARP-DERIVED COLLUVIUM - DECIPHERING THE TIMING OF PALEOEARTHQUAKES ON THE WEBER SEGMENT OF THE WASATCH FAULT ZONE, NORTH CENTRAL UTAH

The timing of middle to late Holocene faulting on the Weber segment of the Wasatch fault zone, Utah, is constrained by thermoluminescence (TL) and radiocarbon age estimates on fine-grained, fault-related colluvial sediments. The stratigraphy in two trenches excavated across fault scarps is characterized by a stack of three colluvial wedges, deposited in response to three separate faulting events, the oldest of which buried a soil developed on a middle Holocene debris flow. Thermoluminescence age estimates by the partial and total bleach methods and the regeneration method on fine-grained colluvium from the trenches agree within 1 sigma and are concordant with the radiocarbon chronology. A synthesis of the TL and C-14 age estimates indicate that these three faulting events occurred sometime between 4500 and 3500, between 3200 and 2500, and between 1400 and 1000 years ago. Detailed investigation of a sequence of fine-grained, scarp-derived distal colluvium shows that much of the sediment was deposited during < 600-year intervals immediately after faulting. The sedimentation rate of colluvium is inferred to increase shortly after faulting, and TL dating of these sediments provides additional information to constrain the timing of faulting events.