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

我们测量了位于日本本州岩川-静冈大地构造线(ISGL)中部的松本-邦池托断裂(MBTF)周围320个点的重力。结合其他研究所公布的数据，我们建立了均匀密集的重力点分布。这一地区的重力点总数超过600个。我们要强调的是，我们的结果是讨论ISGL地下结构所必需的一流地球物理数据。那里陡峭的水平重力梯度清楚地表明沿MBTF存在倾斜板。那里的重复断层引起的密度扰动成功地解释了观测到的重力低。结果表明，重力资料反映了沿MBTF的逆冲断层运动，并成功地利用GPS确定了重力点的三维坐标。我们首次在日本验证了易位GPS技术使我们能够在不到10分钟的时间内确定重力点的位置，精度优于1米。我们的工作为在山区实现重力点更均匀、更密集的分布开辟了一条道路，在这些地区，常规测量技术对确定重力点的位置几乎没有帮助。

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.