Identifying Faults and Fractures at Different Depths from Airborne Gravity Gradient Surveys over Kujyu and Kirishima Geothermal Areas, Japan

Abstract

Airborne gravity gradiometer surveys were carried out by JOGMEC (Japan Oil, Gas and Metals National Corporation) to investigate the Kujyu and Kirishima geothermal areas in Kyushu (southern part of Japan). An interpretation of the gD_FOURIER_2p3 component of the airborne gradiometer data (equivalent to the Bouguer gravity anomalies) was carried out using some geophysical filtering methods available in the Geosoft Oasis Montaj software.
Low pass filtering with upward continuation was used to separate components of anomalies related to sources at different depths. Another filtering technique, first vertical derivative (1VD) was applied to the processed airborne gravity data to make enhance lineaments.
The lineaments of gravity anomalies are inferred to be associated with fault and/or fracture structures. The final result of this work is a geological structure map of Kujyu and Kirishima area showing the intense fault/fracture zones at four different levels: close to ground surface, +1,000 mRL, +500 mRL, 0 mRL, and -2,000 mRL.