| Title | Testing Methods for Geothermal Exploration in the Pacific Northwest |
|---|---|
| Authors | Cashman, Patricia H.; Peterson, Christopher D.; Louie, John N.; Pullammanappallil, Satish K.; Pancha, Aasha; Sladek, Chris; West, L. Travis |
| Year | 2013 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Cascades; exploration; faults; geophysical methods; magnetic susceptibility; electrical resistivity; seismic refraction; refraction; microtremor surveys; water geochemistry |
| Abstract | The Cascade volcanoes are a potential heat source for geothermal energy in the Pacific Northwest, and both water for heat transport and fault-related fracture permeability are also present in the region. However, many of the geothermal exploration methods that are effective elsewhere (e.g., the Great Basin) are not applicable in areas with abundant moisture and thick soil cover. An efficient method is therefore needed for initial geothermal exploration in the Pacific Northwest; ideally, it must be portable, quick, and inexpensive. To address this problem, we did near-surface magnetic susceptibility, electrical resistivity, and refraction microtremor (SeisOpt? ReMi?) surveys across known fault traces near Mt. Hood to test the efficacy of these tools in identifying faults. As an independent test for evidence of geothermal water, we collected and analyzed spring samples from probable accommodation zone in these faults. None of the geophysical methods used in this study was as good as LiDAR imagery for identifying active faults cutting the ground surface. ReMi passive seismic surveys were the most effective geophysical technique for identifying faults, and also documented the vertical component of slip. Magnetic surveys are good for initial reconnaissance, to identify areas of interest for further studies. Electrical resistivity surveys were not effective for reconnaissance studies in this environment. Spring geochemistry at did not provide the independent evaluation of geothermal potential that we hoped, because of dilution by meteoric water. |