GEOPHYSICAL CHARACTERIZATION OF THE GEOTHERMAL SYSTEM IN PAGOSA SPRINGS AREA, UPPER SAN JUAN BASIN, ARCHULETA COUNTY, COLORADO

Pagosa Springs is on top of a complex geothermal system that has not yet been fully characterized. The town would like to develop its geothermal use but is unsure of the sustainable capabilities of the reservoir. In 2013, Colorado School of Mines and Imperial College of London conducted geophysical surveys to improve the knowledge of the geothermal system. It is likely that meteoric water enters through fault systems, traveling down through fractures to the basement rock. The water is then heated as it travels through the basement rock and then returns to the surface through fractures associated with faults running through the main hot springs.

Geophysical surveys at Pagosa Springs were developed with the understanding that faults would be the primary mechanism for water transport. In order to best image such faults, surveys were conducted along a 6.7km long survey line south of Pagosa Springs, running from west to east. Deep seismic and direct current resistivity surveys along the line imaged both known faults and new faults as possible sources of water transport. Near the eastern end of the survey line, additional faults were detected with the use of electromagnetics and direct current resistivity methods. Additionally, a series of self-potential surveys provided a two dimensional map of water flow, providing a fault location near the eastern end of the survey line that was likely to be source of water flow to the near surface.