The Magnetic Disturbances accompanying the Niigata Earthquake

Abstract

The magnetic variation accompanying an earthquake has been discussed by many investigators. However, the data hitherto obtained seem to be unsatisfactory in the density of stations and the frequency of revisions.
Magnetic surveys were repeated several times in Niigata area before and after the Niigata Earthquake by the Geographical Survey Institute. The analysis of the results of the surveys has clarified the following results.
(1) Magnetic field seems to be disturbed several tens of gammas by the Earthquake.
(2) There might occur more than one anomalous magnetic moments originating from the Earthquake. In the eastern part of Niigata, it seems likely that an upward anomalous magnetic moment had been created during ten years before the Earthquake and has turned downward after the Earthquake.
(3) Remarkable changes in declination are observed accompanying the Earthquake. It appears likely that the anomalous secular change returned to its normal tendency. It is felt that this fact may connect the variation of the earth's magnetic field with an earthquake.