Temporal changes of acoustic and seismic wave radiations: Preliminary results of application on Vulcanian eruptions at Sakurajima Volcano, Japan

Volcanic eruptions generally excite seismic and acoustic waves during their activities. Investigation of relationship between seismic and acoustic waves excited by volcanic eruptions is necessary to understand their mechanism. In this preliminary study, we examine temporal changes of the radiations of acoustic and seismic waves during the Vulcanian eruptions at Sakurajima volcano, giving attention into the energy distributions in time between the acoustic and seismic waves. The results show the characteristics of ratios of acoustic to seismic wave radiation, which can be described as follows: the ratios rapidly decrease for 10 s from the onset, and keep the minimum values for about 10-15 s with gradual increases. Since then, the seismic waves are dominant because the acoustic waves are not well recorded beyond the noise level. These results suggest that the volcanic fluid motions are strong in the shallow parts in the beginning, and the active zone gradually becomes deep.