DISTRIBUTION AND CHARACTERISTICS OF NON-VOLCANIC GEOTHERMAL RESOURCES IN THE SOUTHERN PART OF THE TOHOKU ARC, JAPAN

Abstract

A geothermal resources map of the Tohoku volcanic arc was compiled on a scale of 1:500,000, allowing a better understanding of the geothermal resources and heat sources of the area, according to geology and hot spring geochemistry. The map was created using "ARC/INFO" . Some interesting features in the distribution pattern of the geothermal resources are indicated. Non-volcanic geothermal areas are geographically classified into two types. One is the geothermal areas occurring far from Quaternary volcanoes in mountain and hilly countries, and the other the deep-seated hot water resources in late Neogene to Quaternary sedimentary basins. Most hot springs of the former are closely related with active faults, geologic faults, topographic margin of basins, buried old calderas and intrusive rocks, and those of the latter with topographic margin of basins and active faults. The representative hot springs are selected from each geothermal area as the most productive or the highest temperature springs, and compared each other in terms of related geologic structures, chemical characters, temperatures, total dissolved matters and flow rates of hot springs. Most hot springs are classified into three types: simple hot springs, chemically mixed hot springs and chloride rich hot springs. The temperature and total dissolve matters tend to increase from simple hot springs to chloride rich hot springs, but flow rate slightly decrease. Statistic analyses results in the following relationship. The hot spring temperature increases slightly with total dissolved matters and flow rate, but total dissolved matters decrease with flow rate in certain degree.