Co-Seismic Geomagnetic Variations Observed at the 1995 Hyogoken-Nanbu Earthquake

抄録

Impulsive co-seismic geomagnetic variations were observed at two stations nearly 100 km apart from the source region of the 1995 Hyogoken-Nanbu earthquake (M= 7.2). The maximum amplitude at the main shock was 0.6∼1.0 nT and the duration was 20∼30 seconds. These variations seem to have commenced at the origin time and before the arrival of the seismic waves to the observation site of 17 seconds later. A superposed epoch analysis for the aftershocks also reveals similar geomagnetic variations though the amplitude of them is one order of magnitude smaller than that of the main shock. A crustal dynamo mechanism is discussed as a possible cause of such co-seismic geomagnetic variations.