Structural and Paleomagnetic Analysis of Geothermal Core, Akutan Alaska

Abstract

The Hot Springs Bay Valley geothermal area on Akutan Island, Alaska, showed an increase in the fluid output and temperature between 1981 and 2012 (Bergfeld et al., 2014). These increases were attributed to increased permeability along NW trending faults that were interpreted to have ruptured during a seismic swarm in 1996. In 2010 two unoriented drill cores were collected in Hot Springs Bay geothermal resource area. In this study we reorient sections of the highly fractured core with paleomagnetics to test this model of geothermal reservoir evolution at Akutan. The core is composed of interlayered island arc volcanics and shallow marine mudstones. Paleomagnetic plug samples were drilled from the volcanics. Continuous sections of the core were reoriented using the declination of the remanent magnetization as an indication of geographic north. Structure from motion software, Agisoft Photoscan, was used to create digital reconstructions of the core from photographs. The resulting models were then flattened with a cylindrical projection into a 2D depiction of the outside of the core. Fracture orientations and the relationship between fracture sets were measured from these projections. Preliminary results show the youngest set of open fractures trending NW and dipping to the NE. These structures may be related to NW trending, SW dipping, surface ruptures that were observed across the island after the 1996 seismic swarm.