Abstract
An airborne gravity gradiometry survey was conducted by the Japan Oil, Gas and Metals National Corporation (JOGMEC) in the western part of Kirishima volcano, Kagoshima prefecture, Japan. The density structure modeling was conducted using the six components (Gxx, Gxy, Gxz, Gyy, Gyz, and Gzz) of gravity gradiometry data. The high-density areas were estimated in the northern part of the study area at a depth of 1500 to 1000 m below sea level. These high-density areas correspond to the distributions of the older Kirishima volcano sediments. Moreover, the high-density areas were detected between the Ogiri geothermal power plant and Shiramizugoe geothermal field, which are dominated by geothermal activity. According to the distributions of the isotherm and pressure data at 300 m below sea level, this high-density area divides aforementioned geothermal fields. The low-density areas, which have the WSW-ENE trend, were detected in and around Ginyu and Shiramizugoe geothermal field. These trends agree with the faults that found in the geothermal reservoir. It is possible that these low-density areas indicate the fractured areas that have formed the geothermal reservoir.
