2013年桜島人工地震探査の概要と2008年探査との比較

Abstract

We conducted an active seismic experiment in and around Aira caldera in December 2013, five years after a similar experiment conducted in 2008 in order to detect temporal changes of seismic structure beneath Sakurajima volcano and Aira caldera. We deployed 280 temporary seismic stations, 90% of which were at the same locations used in 2008. Six explosions (S1 to S6) of 200 kg or 300 kg of dynamite were sequentially detonated during the night of 5 December 2013. All of the shot locations expect S3 are less than 60 m from the 2008 locations. We undertook continuous seismic recording for 9 h during the night: the obtained records contain both the waveforms excited by the six shots and those from an explosive eruption and volcanic tremor. To evaluate the changes of subsurface structure beneath Sakurajima volcano since 2008, we calculated cross-correlations of waveforms recorded at all of the recording stations that duplicated those of 2008. The most cross-correlations are equal to or greater than 0.7.