Permalink : http://hdl.handle.net/2115/38163

JaLCDOI : 10.14943/gbhu.72.331

Meakandake volcano is located southwest on the Akan caldera rim, the eastern part of Hokkaido. Four small eruptions occurred at Meakandake from January to February, 1988. Seismic activity was higher for one year including this eruption stage. Research Center for Earthquake Prediction of Hokkaido University (RCEP) installed temporal seismic array on the northwest flank of the volcanic edifice twenty days before the first eruption in order to clarify characteristics of seismicity associated with volcanic activity. Daily number of earthquakes became suddenly decreased, three days before the first eruption. And hypocenters were estimated to be very shallow by seismic amplitude ratios. After March 1988, deep low frequency events occurred frequently. During the observation, so various types of waveforms were recorded that we classified seismograms broadly in two groups. One is "simple event" and the other is "complex event". Mechanism of "complex event" is not so simpler than that of "simple event". "Simple event" is subclassified into three; HF, LF and PT. "Complex event" is subclassified into four; TD, TS, LD, and T. Dominant frequency of waveforms of "simple event" splits to 6 - 8 Hz and 10 - 13Hz, which correspond to LF and HF, respectively. There were four seismic swarms after eruptions. Waveforms in every swarm were so similar one another. Although they were, namely, earthquake family, they were able to be classified to LF and HF. And their first motions of seismograms were the same direction. In order to explain these characteristics, we proposed the tensile crack model with Doppler effect.