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.