Comparative Study of the Subsurface Thermal Structure in Northern Honshu, Japan, Based on Normalized Temperature Data and Solute Geothermometers

To promote geothermal development in Aomori Prefecture, Japan, this study compiled a database of the geothermal resources of the prefecture, which included chemical data for 786 hot springs, temperature data for 26 natural springs, and subsurface temperature data for 35 wells. A map of the activity index distribution for the entire prefecture was also developed using the Aomori Prefecture Geothermal Resource database, and its efficiency was discussed by comparison with the distribution of Quaternary volcanoes and the temperature distribution map calculated using quartz and Na-K solute geothermometers. The activity index distribution map for the entire prefecture showed a good fit with both the distribution map of a region with a sharp eastern edge of low-velocity zones in the mantle wedge and the volcanic front, as well as the temperature distribution map calculated using the quartz and Na-K geothermometers. This reflected the effectiveness of the developed map, which indicated the Hakkoda-san and Hiuchi-dake areas as promising for geothermal development. Given that the activity index distribution map is easy to use, it could become a method of assessment, in conjunction with temperature distribution maps calculated using solute geothermometers, for detecting promising areas in the early stages of geothermal exploration.