5-12. Joint volcanological experiment on volcanic structure and magma supply system

 

   Since 1994, joint experiment has been conducted in several volcanoes in Japan to reveal the structure and the magma supply system by the scientist group of national universities under the National Research Project for Prediction of Volcanic Eruptions (Fig.1).  Volcano Research Center conducts and promotes this experiment.  The experiment was carried out by seismological, electromagnetic and other geophysical methods.

   Seismic explosion experiments succeed to determine a precise velocity structure up to 3km in depth by high-density observation network and newly developed seismic tracing method. In recent years, new method, which combines teleseismic and gravity data, succeeded in detecting some anomalous regions related to magmatic activity in Izu-Oshima Volcano. Similar technics will be applied in Fuji Volcano in 2003.

 Electromagnetic survey found that the deep low resistivity region about 10 km below the surface, and the shallow low resistivity region about 1 km below the surface.  Shallow low resistivity region, which is interpreted as a water-saturated porous layer, plays an important role in controlling types of eruption and in generating precursory phenomena of volcanic eruptions.

Fig. 1 Joint volcanological experiment on volcanic structure and magma supply system in Japan.

Fig.2 Shot point on the hoot of Hakkaido-Komagatake Volcano.