Subsurface Structural Mapping Using Gravity Data of Hohi Geothermal Area, Central Kyushu, Japan

Abstract

Hohi area is located in central Kyushu island of Japan and is known as a volcano-tectonic depression region. The area is characterized by its potential geothermal resources. In this study, we attempt to delineate the subsurface structures of the area using integrated interpretation of existing gravity data. The gravity survey of Hohi area is about 500 km2. The total number of gravity stations was up to 1500 and average distribution of stations was approximately 3 per km2. Interpretation of horizontal gradient of the gravity data indicated that the area is characterized by the existence of high gradient anomalies associated with existing geothermal fields and manifestations. Horizontal gradient analysis also enabled tracing several faults that are mainly striking in the S-N, NW-SE, and NE-SW directions. Euler deconvolution method has been applied to the gravity data and provided fast information about both the depth and trends of the shallower subsurface structures in the area. Depth to deeper structures, based on modeling of the gravity data, is found to be about 5.4 km.