Interpretation of earthscope magnetotelluric data for Northwestern United States

In this dissertation, I present the results of large-scale three-dimensional magnetotelluric (MT) inversion, based on the nonlinear conjugate gradient algorithm and the contraction integral equation forward modeling method, applied to data collected in Northwestern United States for part of the EarthScope project. It is shown that the most noteworthy anomalies within the inverse geo-electrical model are resistive structures associated with oceanic lithosphere and cratons, and conductive features associated with mantle upwelling. Density estimations from seismic data analysis show upwelling phenomena in the upper mantle where Yellowstone is the present-day surface expression of the deep heat source. Comparison of MT results to approximately 400 km depth have reasonable correlation with P-wave and S-wave velocity models obtained from seismic tomography. The MT inversion demonstrates that strong resistive zones line up along the northwest coast correlating to recent seismic interpretations of old oceanic slabs at 100 km depth believed to be remnants of the Farrallon oceanic plate. This dissertation shows that access to multiple physical properties within the subsurface increases our ability to understand complexities in geological interpretations resulting from the interplay of transforming quanta at differing pressure and temperature regimes with depth. Therefore, EarthScope is proving true to the founding philosophy that the bold, new experiment will fundamentally change our view of the planet.