Modelling of Deep Geological Structure Estimated From Gravity Pattern with Density Measurement in the Hatchobaru Geothermal Field

Abstract

A detailed gravity survey with station intervals of about 120- 250 meters was carried out in the Hatchobaru geothermal field in centd Kyushu to estimate the deep geological structure. A Bouguer anomaly map was compiled from 475 gravity measurement data which included previously recorded data. The density correction factor, p , was determined to be 2.25 g/cm3. The Bouguer anomaly ranges from - 28.7mgal to - 7mgal. The Hatchobaru power station is situated in a local low-gravity anomaly zone. Seven gravity lineaments are estimated from the detailed Bouguer anomaly map. The NW-SE lineament in the eastern part of the survey area is considered to be a large-scale fault dipping towards the east, which is a main passage for the deep geothermal fluids in the Hatchobaru area. Detailed gravity surveys with closely spaced stations are found to be effective to estimate deep geothermal structures.