1983 年4月8日浅間山の噴火に伴う長周期地震波の解析

抄録

An explosion earthquake associated with the explosive eruption of Mt. Asama on April 8, 1983 was recorded by long-period seismographs at Matsushiro Seismological Observatory, JMA. The long-period seismograms assist in examining the general dynamic process of the explosion earthquake. These data are interpreted as waves excited by counter forces of the eruption and a stress change associated with the eruption. As a source model of the stress change, we assume a double couple force. The general dynamic process inferred from the long-period seismograms is as follows : the counter forces were applied at the start of eruption and about 17 seconds later. These impulses are estimated as 8×10¹⁵ and 1×10¹⁶ dyne・sec, respectively. About 10 seconds later from the start of the eruption, the strike-slip type stress change of north-south compression occurred. The seismic moment of the stress change is estimated as 3.2×10²¹ dyne・cm. This type of stress change associated with the eruption may be interpreted as the stress release along tectonic faults around Mt. Asama.