A TEST OF GEOPHYSICAL METHODS FOR GEOTHERMAL EXPLORATION IN THE PACIFIC NORTHWEST: MT. HOOD, OREGON
Although the Cascade volcanoes clearly represent a potential source of geothermal energy, the high rainfall, meltwater from glaciers and permanent snowfields, and resulting thick soil cover and dense vegetation in the region rule out many of the exploration methods that are effective in other environments. This study entailed a series of near-surface, small-scale geophysical surveys across Q fault traces that had been previously identified on LiDAR imagery. The study area spanned an accommodation zone between the west-dipping normal faults of the Q Blue Ridge fault zone, and the east-dipping normal faults of the Q Gate Creek fault zone. The pervasive fracturing associated with accommodation zones makes them favorable structural settings for geothermal activity. Surface water samples for geochemical analysis were collected at Blowdown Ridge, in the accommodation zone.
Although none of the geophysical tools used in this study provide direct evidence of geothermal resources, some of them could be useful in reconnaissance exploration in the Pacific Northwest. In this study, shallow refraction microtremor (SeisOpt® ReMi™) surveys were second only to LiDAR imagery in their ability to locate faults. Magnetic surveys are promising for initial reconnaissance, to identify areas of interest for further studies. Both are portable, quick and relatively inexpensive.