Abstract
At Kuchinoerabujima Volcano located in southwest Japan, eruptions occurred on August 3, 2014, and May 29 and June 18, 2015. We evaluated the seismic and acoustic waves excited by these eruptions to characterize the eruptions. First, we estimated the eruption durations at a single station. The durations were 50 s, 6 min, and 6 min for the eruptions on August 3, 2014, and May 29 and June 18, 2015, respectively. The seismic and acoustic waveforms of the 2014 eruption have spindle shapes, while the waveforms of the 2015 eruptions have initial impulsive phases followed by weak arrivals. These three eruptions were phreatomagmatic in nature, as suggested by geological surveys. Second, we estimated the seismic and acoustic energies of the eruptions. The seismic and acoustic energies of the 2014 eruption were 1.88 GJ and 0.21 GJ, respectively. The seismic and acoustic energies of the eruption on May 29, 2015 were 0.36 GJ and 2.2 GJ, respectively; and the seismic and acoustic energies of the eruption on June 18, 2015 were 0.3 GJ and 0.06 GJ, respectively. Third, we estimated the counter single force excited by the eruptions on May 29 and June 18 by using seismic waveform matching at a broadband station. The pulse width and amount of the counter force were lined on the scaling line for a conduit pressure of 6 MPa. For the 2014 eruption, the short duration and spindle-like waveforms may reflect that the eruption was short lived and initially weak, gradually becoming violent and forming fissures, while the 2015 eruptions did not form new fissures.
