Studies on the Bouguer anomaly of active faults along the western margin of the Kanto plain

在东京都西部约1,700平方公里的范围内，用LaCoste和Romberg重力仪在约1,500个测站进行了重力观测，以弄清那里的断层结构。结果表明：（1）本次调查新发现的儿玉断层、串比木断层和春日川断层为一条连续的断层线。1931年的西琦玉地震可能是由这些断层的联合运动引起的。(2)从地形学的观点来看，立川断层被认为是一个向西南方向沉降的垂直断层，然而，目前的重力测量得出的结论是，该断层可能是一个左旋走滑断层，包括垂直位移。

Gravity observations were made at about 1,500 stations with a LaCoste and Romberg gravimeter over an area of about 1,700 km_2 in the western part of the Tokyo metropolisphere for the purpose of clarifying fault structure there. Our conclusion is as follows:(1) The Kodama fault (newly discovered by the present survey), the Kushibiki fault and the Kasukawa fault stand continuously in a single fault-line. The 1931 Nishi-Saitama earthquake may have been caused by a joint motion of these faults.(2) From the topographical point of view the Tachikawa fault is considered to be a vertical fault subsiding southwestward the present gravity survey concludes, however, that this fault may possibly be a left-lateral strike-slip fault including vertical displacements.