Gravity Anomaly Distribution and 3-D Density Structure in the Chugoku and Shikoku Districts, Southwest Japan

Abstract

Gravity data measured at '9, 500 stations in the Chugoku and Shikoku districts, south west Japan, were used to construct a detailed contour map of the regional Bouguer anomaly . We performed a crustal density inversion of the Bouguer anomaly data by means of a damped least squares method combined with singular value decomposition over a 280 km×180 km area. The resultant three-dimensional density structure reveals the following features: a low density, elongate belt along the Median Tectonic Line from Kyushu to east Shikoku; a high density structure beneath the central Seto Inland Sea; a lowdensity structure with local minima distributed widely beneath Chugoku; high-density belts beneath Shikoku corresponding to known geologic structures of the Sanbagawa and Mikabu belts.