Infrasonic precursors to a Vulcanian eruption at Sakurajima Volcano, Japan

The May 1998 eruption sequence of Sakurajima Volcano was monitored by ten infrasonic stations, ten seismometers, and a video camera. During this seismo-acoustic experiment, we recorded hundreds of infrasonic tremor and long-period events associated with seismic signals, and observed a progression from relative quiescence to a Vulcanian eruption. The number of infrasonic events increased with escalating volcanic activity, and the dominant character of the infrasonic signals changed from impulsive to emergent. At 22:17 of May 19, Sakurajima released ash and gases to a height of 2 km above the vent, an event that was recorded continuously by one infrasonic and two seismic stations. We present the experimental setup as well as a procedure through which infrasonic signals may be incorporated into future eruption monitoring and forecasting algorithms for open-vent volcanic systems. In addition, our recordings suggest that infrasonic signals are more representative of processes occurring within the volcanic interior than are seismic signals, which are strongly altered by diffraction and scattering in the volcanic edifice.