Estimation of near-surface porosity distribution using Bouguer anomaly

Abstract

　We proposed a method for estimating porosity using the Bouguer anomaly by replacing the density structure with a porosity–density contrast combination between the pore fluid and host rock. We applied this method to Bouguer anomalies obtained in Jigoku-dani, which is located in Midagahara volcano, and it was predicted that low-density areas filled primarily with volcanic gas and/or water would have a porosity contrast 0.06 – 0.35 higher than the surrounding host rock. Comparisons with effective porosities based on existing well data in geothermal areas and analyses of the relationship between porosity and density revealed that the estimated porosities in this study would be distributed across a range of realistic values.