In order to evaluate the geothermal potential of a project area on Adak Island, Aleutian Islands, Alaska, a high gain (40-750K), high frequency (5-30hz) microseismic network was operated for a period of ten days in late October, 1974. The detection threshold determined from the recurrence curve was found to be below magnitude 0.0. Over 35 local events (S-P time less than four seconds) were detected, of which 26 events can be associated with a postulated fault in Andrew Bay near Mount Adagdak on the north side of Adak Island. First motion studies indicate that this fault is a right-lateral strike-slip fault with a small thrust component. Temporal and spatial variations of Poisson's Ratio within the interpreted fault zone (derived from velocity ratios and Wadati diagrams) have led to the derivation of a theoretical model of a dilatant region near Mount Adagdak. This region is interpreted as having the largest potential of the area surveyed for producing commercial earth steam