On the Results of Geomagnetic Observations for Earthquake Prediction Research in the Eastern Part of Hokkaido
Mori, T., Mizuno, Y. & Hasegawa, K.
Abstract
Memambetsu Magnetic Observatory has made the observations of the geomagnetic absolute values once a year since 1971 at three temporary stations (Attoko, Kamishunbetsu and Midori) in the eastern part of Hokkaido, for the earthquake prediction research.
At each station an undisturbed site where the gradient of the geomagnetic field was negligible were selected and a portable proton precession magnetometer and a GSI-type first order magnetometer were employed for the observation. In order to reduce the position error at resetting of the magnetometers, a permanent mark made of non-magnetic material was buried for each one of the magnetometer position, and brass rods were also buried around the mark for the tripod of the magnetometer to help to reset at the right position.
On June 17, 1 973, the Earthquake off the Nemuro Peninsula occurred. Then, at three stations the observations were made soon after and at Attoko again on July 17 and Nov. 6. In order to eliminate the local differences of solar daily variation, the observations were carried out at night.
The weighted differences between the observed values at each station and those at Memambetsu were computed. Changes of the difference are nearly within the observational error except D component at Attoko. The change of the weighted difference of D at Attoko amounted to about 0.8' just after the earthquake. This is anomalous and seems to be the seismo-magnetic effect of the Earthquake off the Nemuro Peninsula.
