Spatial variations in catchment-averaged denudation rates from normal fault footwalls

Abstract

We test the spatial correspondence between rock uplift in active normal fault footwalls in the western USA, and catchment-averaged denudation rates from cosmogenic radionuclide (CRN) analysis. We find that denudation rates vary along strike, depending on the fault length and displacement. For the 18-km-long Sweetwater fault, foot-wall relief is largely inherited from the prefaulting topography, and denudation rates are only partly reflective of fault displacement. For the 130-km-long Wassuk fault, all inherited topography has been removed by erosion in response to fault displacement. Denudation rates, however, show little along-strike consistency and no correlation with catchment size or morphology. We argue that, in the early stages of fault growth, CRN-derived denudation rates reflect inherited prefaulting relief, with an overprint of fault-controlled erosion. In later stages of fault growth, rates are decoupled from fault displacement through the impact of stochastic landsliding events, and longer term measures of denudation (such as low-temperature thermochronometry) that integrate over multiple earthquakes may provide a better record of spatial variations in rock uplift.