The Study of Eruptions and Earthquakes originating from Volcanoes : Part I. Some Statistical Relations between Explosive Eruptions and Earthquakes of Volcano Asama

Abstract

On the basis of seismometrical investigations, the writer studied the relations between the eruptions and the earthquakes from various volcanoes in Japan. Judging from reports with respect to volcanic eruptions and earthquakes originating from volcanoes, it seems that seismic activities preceding the eruption depend not only on the magnitude of eruption and the structure of volcano but also on the viscosity of lava at the time of eruption. This is rather natural because higher viscous lava will receive larger resistance in the course of its elevation from the magma chamber to the earth’s surface, and as a result, larger stress will be produced inside and under the volcano. In this paper, the writer reports in a condenced form a statistical relation concerning the frequency of earthquakes and explosive eruptions of Volcano Asama. The Asama earthquakes dealt with in the report are mainly those observed by comparatively low magnificatian (T = 1.0sec, V = 350) at the Asama Volcano Observatory which is situated at 4.2km E from the center of the summit crater. From the present investigation, it was made clear that most of the explosive eruptions were preceded by an increase in unfelt earthquakes. In addition, an experimental formula useful for predicting volcanic eruptions was given by the statistical relations based on the frequency of earthquakes originating from the volcano and the occurrence of explosive eruptions of Asama. In the forthcomming report (Part II), the same problem will be discussed on the basis of observations made by means of seismographs of higher magnification which were set nearer the summit crater.