Terrestrial Heat Flow Determinations in Central Kyushu, Japan

Abstract

Ten new heat flow values were determined by using geothermal well data and water well data in central Kyushu in addition to one new value in southern Kyushu. As a result, the existence of the high heat flow zone (higher than 2 HFU) became clear. Almost all the volcanoes, hot springs and other geothermal manifestations in central Kyushu exist in this high heat flow zone. Underground temperatures were calculated based on the equation of heat conduction in the steady state. Generally, temperatures amount to 330℃ at 10 km deep, 620℃ at 20 km and 940℃ at 30 km deep. Accordingly there may exist a zone of partial melting of rocks beneath the Moho discontinuity in central Kyushu. In the Kuju area, which is located in the eastern half of central Kyushu, there is a possibility that partial melting occurs at such a shallower depth as 10 to 15 km.