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, footwall 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.