2. 噴火地震活動(V. 秋田駒ケ岳 1970-71 年の噴火現象)

概要

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About 33, 000 eruption-type and 30 A-type earthquakes were observed during the whole activity. The analysis of the observed data shows that the eruption activity may be affected by the occurrence of an earthquake (M=6.2), which was located at distance of 60km from the volcano. The m value of the Ishimoto-Iida's relation for eruption earthquakes is evaluated to be 2.5-2.9 by the three authors. Two authors reported that the relation between number and amplitude differed for large and small amplitude parts, whereas another author adopted a single relation for whole range of amplitude. The discrepancies may be due to the difference in instruments and procedure of analysis. The initial motion was always compression except for a few number of earthquakes. One author estimated the depth of hypocenter to be less than 50m, while another reported that the depth reached down to about 700m and the vent may be inclined to north of the crater. The partition of eruptive seismic energies may have changed with time.
1971-12-01