Gravity anomaly of the middle part of the Fossa Magna -- Matsumoto Bonchi Toen Fault

点击翻译按钮获取中文摘要

We measured gravity at 320 points around the Matsumoto-Bonchi Toen Fault (MBTF) which is located in the middle part of the Itoigawa-Shizuoka geotectonic line (ISGL), Honshu, Japan. Combining data published by the other institutes, we established homogeneous and dense distribution of gravity points. The total number of gravity points in this area exceeds 600. We would like to emphasize that our result is the first-class geophysical data essential to discuss the underground structure of the ISGL.The steep horizontal gravity gradient there clearly indicates the existence of a dipping slab along the MBTF. The density perturbation due to repeated faulting there successfully explains the observed gravity low. We conclude that the gravity data reflect the thrusting fault motion along the MBTF.We succeeded in using GPS (Global Positioning System) to determine 3-dimensional coordinates of gravity points. For the first time in Japan, we verified that the translocation GPS technique enables us to determine position of gravity points in less than 10 minutes with accuracy better than 1 meter. Our work leads a way to realize more homogeneous and denser distribution of gravity points in mountainous areas where conventional surveying technique was of little help to determine their positions.