諏訪之瀬島火山における火口に近接した地震計アレイ観測 -2010年10月～11月実施-

Abstract

We conducted a small-aperture seismic array observation at Suwanose-jima volcano for the period from 1 October to 18 November 2010. The seismic array consists of 13 elements of short-period seismometers and 5 data loggers. We perform array analysis for continuous seismic records observed during this period to investigate the wave-field properties of several episodes of volcanic tremors and 30 explosion earthquakes. Averages of the slowness values and back azimuths of volcanic tremors are estimated to be 0.8-1.4 s/km and 0°-40°, respectively. This suggests that the tremor wave consists of body and surface waves that propagate from the active crater. The array analyses and particle motions of explosion earthquakes indicate that the initial parts of the waveforms of explosion earthquakes are S waves that come from the direction of the active crater. The slowness values of the S waves of the explosion earthquakes are 0.3-0.5 s/km. Variation of the slowness value reflects the depth change of the explosion sources.