日本列島の重力異常陰影図

(II) フォッサマグナ周辺の重力異常陰影図と地質構造

抄録

With an aid of geophysical and geological information, we discussed relationships between characteristic patterns of the shaded relief maps of gravity anomalies and subsurface structures in and around the Fossa Magna region, central Japan. Lineament-like distributions of gravity anomalies are one of the characteristic patterns in the shaded relief gravity anomaly maps in this area. Such lineaments of gravity anomalies are presumably caused by fault like structures which are covered by thick sediments or volcanic products. A very large (about 80km) gravity depression is also clearly appeared over the Kanto-Plain. This depression represents a basin structure in this area. The shaded relief maps are also suggesting a number of pull-apart structures of basement rocks. We also examined relationships between distribution of shallow earthquakes and lineament-like patterns of gravity anomaly. Although we could not find apparent correspondence between the linearment-like patterns and smaller earthquakes, better correspondence for larger, magnitude grater than 6.0, ones. These results presumably indicate that the shaded relief maps provides new tool for exploring hidden faults and other subsurface geologic structures.