Spatial Scales in Topography and Strain Rate Magnitude in the Western United States

Spatial spectral analyses of topography and strain rate magnitude across the western United States reveal the presence of at least two separable spectral peaks, representative of characteristic length scales, one short (~10–50 km) and one long (~150–250 km). Less spectral power at intermediate wavelengths aside from that expected for a red, or power law, spectrum occurs in either data set. These results quantify previous qualitative observations that the topography of western North America contains both short and long characteristic wavelength features. Comparing the spectral results to simplified bounding solutions for elastic, viscous, and layered models under tension shows that multiple spectral peaks of comparable power can be reproduced only by mechanical models with more than one layer. Therefore, the simplest model of lithospheric architecture capable of generating the observed dominant characteristic length scales is an elastoplastic lid over a viscous layer.