4 - 5 Designing and manufacturing of penetrator-type seismographs

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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.

Conceptual illustration of seismic observation by use of a penetrator-type seismograph.

The trial piece used for testing at Unzen Volcano.
The body of penetrator is made of aluminium alloy. The penetrator-type seismograph consists of a seismograph, a thermometer, a battery, a set of signal amplifier and transmitter.

The helicopter from the Nagasaki Prefecture Disaster Prevention Office is heading for the test site of the Mt. Fugen with a trial penetrator beneath it.
The trial penetrator dropped from the helicopter well penetrated into pyroclastic deposits.

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