Abstract
Four types of volcanic earthquakes and two types of volcanic tremors are observed at Asamayama volcano. They are named A-type earthquake, B-type earthquake, T-type earthquake, explosion earthquake, short period type volcanic tremor and long period type volcanic tremor, respectively.
Relations betw e en amplitudes (A) and durations (t) of the vibrations of each type of volcanic earthquake are expressed in the form of t=kAα, but the two types of volcanic tremors are not explessed by this equation. In this equation, a is 0.4 for every type of volcanic earthquake, and the value of k is 104.7 for T-type,37.8 for A-type and 35.5 for B-type earthquakes.
The value of m in Ishimoto-Iida's relation is calculated to be 1.9 for A-type earthquakes,3.2 for B-type earthquakes and 1.0 or 3.2 for T-type earthquakes.
The spectra of seismic waves for each type of volcanic earthquake are compared, using the data of three component seismograms at three observation stations. The maximum value of the spectrum is detected at 4 Hz for A-type, at 2--3 Hz for B-type and at 1.5 Hz and 2-4 Hz for T-type earthquake. The prevailing periods of seismic waves of the explosion earthquakes are 1 sec., and those of the short period type volcanic tremors are 0.3-0.5 sec., and of the long period type volcanic tremors are 0.6-0.8 sec.
The above-mentiond different values for each type of volcanic earthquake and volcanic tremor clearly show the features of different types.
The frequency of occurrence in percentag e of each type of volcanic earthquake during the period from 1966 to 1977 was 99.60% for B-type,0.20% for A-type,0.13% for T-type and 0.06% for explosion earthquakes.
The relation between the vo l c anic eruption and the A-type earthquake is remote, and that between the B-type earthquake and the short period type volcanic tremor is close. But the T-type earthquake and long period type volcanic tremor are not so closely related to volcanic eruptions.
