5-13. Comprehensive Observations at Specific Volcanoes

 

   Under the national project for prediction of volcanic eruptions, we have conducted comprehensive joint surveillance at a specific volcano per year in order to obtain basic data for the better understanding of eruption mechanisms and current volcanic activities.  The target volcanoes during the sixth 5-year plan (1999-2003) include Iwate, Satsuma-Iwojima/ Kuchinoerabu-jima, Unzen, Fuji and Kusatsu-Shirane volcanoes. At Unzen volcano, we detected a re-inflation centering beneath the western foot of the volcano after the cessation of lava effusion in 1995. We also detected the temporal variations of the activities of Iwate volcano that started in 1998. We could detect essential data on precursors to the recent eruptions in 2000 of Usu and Miyakejima volcanoes. Especially after the beginning of the activity of Miyakejima, we detected a large amount of deflation whose source was located at the same position as that of the inflation before the eruption, and could estimate the magma storage zone.

   In the joint observation at Fuji volcano in 2002, we started a dense seismic observation by installing 30 seismometers around the volcano in addition to the permanent stations operated by several institutions, in order to clarify the mechanism of low-frequency earthquakes originating deep beneath the volcano and to make 3D seismic imaging of the subsurface structure (see, 4-4 Fuji). We also conducted an advanced hybrid gravity survey by integrating absolute and relative gravity measurements, and self-potential and MT surveys across the volcano.

Fig. 1. VSAT telemetry system installed within the fight-exercise field of Self Defense Force at the eastern foot of Fuji volcano.