Publication Date

12-2013

Date of Final Oral Examination (Defense)

7-11-2013

Type of Culminating Activity

Dissertation

Degree Title

Doctor of Philosophy in Geophysics

Department

Geosciences

Supervisory Committee Chair

Kasper van Wijk

Supervisory Committee Member

Lee M. Liberty

Supervisory Committee Member

Mila Adam

Abstract

We use an array of existing and modified geophysical techniques to investigate the active Seattle thrust fault zone in western Washington and a geothermal system at Mt. Princeton Colorado. Through the integration of different geophysical methods, we can extend our observations of the surface geology to beneath the subsurface, thereby giving us a greater understanding of the structures and their kinematic interplay.

We find geophysical evidence through the use of potential field and seismic data for the Seattle fault zone extending further to the west than previously thought. We also find evidence that the Seattle fault zone may be linked to active fault systems further to the south and west. These findings suggest a larger magnitude earthquake can be sustained on the Seattle fault zone and this has implications for earthquake hazard assessment in the region, as these systems pass under the densely populated urban developments of both Seattle and Tacoma.

The second part of this work is based at the Mount Princeton Hot Springs located in the Upper Arkansas basin in central Colorado. These springs are the result of a lateral offset in the basins major range-front normal fault, termed the Sawatch fault. Imaging and characterizing the near surface of this lateral offset through the use and development of near surface geophysical methods improves our understanding of this geothermal resource. Faults in these geothermal systems can form rapid transport pathways for deep-heated geothermal fluids to migrate upwards into the near surface. We chose two separate field sites that exhibited high geothermal activity hypothesized to be a result of the lateral offset across the Sawatch fault. Both sites are on the order of 0.1 km2.

At the first site, we used a 3D refraction survey in conjunction with self-potential and resistivity surveys to determine the near surface structure and underground hot water pathways of the Mt. Princeton geothermal system. We find a number of northwest to southeast striking faults that at our site that suggest the Mt. Princeton hot water springs are being fed from a system to the northwest. These structures are likely connected to the main Sawatch normal fault that bounds the western margin of the Upper Arkansas valley.

At our second site, we acquired a 440 m long multi-component, high resolution seismic survey. The purpose of this survey was to both explore a modification of a surface wave analysis technique, called the Spatial Autocorrelation Method (SPAC) and map the near surface structure. The seismic survey was selected to be coincident with a 160 m deep well that showed a hot water source at a depth of 150 m. We conducted a vertical seismic profile on this well to help constrain our surface seismic survey. We found that adding extra components to the SPAC method improves both signal-to-noise and our spatial resolution of the 2D subsurface velocity profile.

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