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Because of very frequent
occurrence of pyroclastic
flows of which deposits
covered almost the whole part
of the slope of the volcano,
setting up of
observation sites was limitted
within very narrow areas during the
eruption.
This made us difficult
to keep high-level observations
of the volcano.
Therefore we designed
and developed penetrator-type
seismographs
in cooperation with
the Institute of Space
and Astronautical Science (ISAS)
to execute high-level observations
in dangerous zones close
to the active crater
and lower reaches of
pyroclastic flow deposits.
This seismograph can
penetrate deep into
the ground when it is
droped from a helicopter.
This seismograph should
withstand the impact schock
sevral thousnads times
the graviational acceleration,
when it penetrates into the ground.
Accordingly it should show
the high achievement of
shockproof performance.
We repeated tests of
dropping from the air
to improve it for the practical
use at Unzen Volcano.
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