Operation Test of Artificial Seismic Prospecting around Active Crater in Aso Volcano

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The two observation experiment in November and December 1998 had been clarified. a basic structure of the magma system in Aso Volcano.1.Initial Motion Reading : Reading work of initial phases of artificial earthquake was composed by the expert researchers, and selected the most appropriate value individually examining two or more reading values. Because the Naka-Dake crater is now active, and the subsurface structure near the crater especially is showed to be complicate, and the volcanic tremors always occur, and the initial phase amplitude was small, the reading of the initial motion was difficult. As a result, the anomalies of travel time have been recognized near the crater and the reflective waves have been read from the crater to Kusasenri region.2.Refraction Method Analysis : The 2-dimension velocity structure has been analyzed, and have been compared with the traditional model.3.About the reflective plane : The travel times of reflective waves have showed the shape of magma reservoir at the region of 3km in depth of 3km west from the crater. This result is thought to be a reflection wave from the head of the magma reservoir of Aso Volcano, which centers on Kusasenri about 6km depth in the underground of 2-3km in the radius.4.About the Observation of Volcanic Tremors : At this experiment, the volcanic tremors was observed. A lot of volcanic tremors were observed with the deliberate observation stations, which had been developed around the crater. The hypocenter of volcanic tremor has been presumed to be just beneath the crater. The focal mechanism of tremor have been included the element of double couple.5.Reflection Method near the Crater : By the mini-vibrator the western subsurface region of the crater has been analyzed.These results were printed as a report and distributed.