Seismic exploration at Fuji volcano with active sources : The outline of the experiment and the arrival time data

Fuji volcano (altitude 3,776m) is the largest basaltic stratovolcano in Japan. In late August and early September 2003, seismic exploration was conducted around Fuji volcano by the detonation of 500 kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an eigenfrequency of 2 Hz were used for observation, positioned along a WSW-ENE line passing through the summit of the mountain. A total of 469 seismic stations were installed at intervals of 250-500 m. The data were stored in memory on-site using data loggers. The sampling interval was 4 ms. Charges were detonated at 5 points, one at each end of the observation line and 3 along its length. The first arrival times and the later-phase arrival times at each station for each detonation were recorded as data. P-wave velocities in the surface layer were estimated from the travel time curves near the explosion points, with results of 2.5 km/s obtained for the vicinity of Fuji volcano and 4.0 km5/s elsewhere

A fundamental study to detection of magma transfer from Aira caldera

本報告書中の、桜島火山における反復地震探査(2013年観測)(2014-06) 京都大学防災研究所年報. 57(B): 138-149の最終版はhttp://hdl.handle.net/2433/196150からご覧いただけます。関連リンクをクリックしてください

Active Seismic Source Experiment in and around Sakurajima Volcano in 2013 and Comparison with the Experiment in 2008

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.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