Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name


Department or School/College

Department of Geosciences

Committee Chair

Rebecca Bendick


Geophysics, tectonics, spatial scaling


University of Montana

Subject Categories

Geophysics and Seismology | Tectonics and Structure


Deformation of continental lithosphere can extend great distances laterally from tectonic plate boundaries. This extent has been used to argue for a variety of constitutive laws for continental materials, based on the underlying principles in continuum mechanics that identify a relationship between characteristic spatial scale and material properties. Although the relationship between observed deformation and material models is always non-unique, quantifying one or more characteristic scales of deformation in a region can rule out some models of how the lithosphere deforms. In the western United States active deformation occurs at the plate boundary between North America and either the Pacific or Farallon plates, and extends east as far as the Rocky Mountains, a distance greater than 1000 km, hence further than any elastic dislocation plate boundary model allows. This study seeks to identify spatial patterns in the deformation as a means of quantifying characteristic scaling using two different observational datasets: topography and strain rate constructed from GPS velocities and earthquake focal mechanisms. Methods from the field of Fourier analysis are used to extract the characteristic scales of deformation and map the relative prominence of the characteristic scales spatially. Power spectra of the datasets, strain rate and topography, shows two distinct characteristic frequency bands (the inverse of spatial wavelength). Two frequency bands are identified, one covering 0.02-0.1 km-1, interpreted as an elastic frequency band, and the second covering scales from 0.004-0.006 km-1, interpreted as a viscous frequency band. A summation of power from each frequency band within a windowing function allows for the creation of power summation maps that show the relative prominence of each frequency band. From the power spectrum summation maps, dominant frequency maps are also created to show which processes are more prominent regionally. From the analysis of the power spectra and power summation maps we find that topography in the western United States is generated through a combination of elastic and viscous processes with past tectonics and erosion altering some of the elastic frequency features.



© Copyright 2016 Cody W. Bomberger