Magnetic Anomaly and its change in the proposed site of new standard magnetometer in the Kakioka Magnetic Observatory
Construction of new modernized system of standard magnetic observation is now going on in our observatory. New site, in which new houses of standard magnetometer will be built, was reconstructed in Autumn, 1970 to widen the flat area. Repeated magnetic surveys have been made in and near the flattened ground after the reconstruction. A part of the result of the survey is reported preliminarily in this paper. First, the distribution of total intensity is compared with that of the survey made by Ochi before the reconstruction. His complicated local anomalies due to topography and old house removed by the reconstruction have disappeared.
Then it is ascertained that sufficient area of small field gradient is obtained in the central part of the flattened ground to construct the new system. Next, the change of the total intensity with time after the reconstruction is examined using weekly measurements at 19 observation points in the ground. At all 19 points, the total intensity decreases gradually and its amount reaches 1-2γin 2.5 months. The susceptibility of the soil at the central part of the ground, which is newly exposed after the overburden soil were removed by the reconstruction, is smaller than the expected from the old surface soil. This gives a favourable result to construct the base of the house or pillar in the soil.