高分解能な3次元地震波速度構造解析による姶良カルデラ下のイメージング

抄録

We obtain a three-dimensional seismic velocity structure below the Aira caldera at a depth shallower than 15 km, southwest Japan, applying seismic tomography inversion method to analyze 14,652 P-wave onsets and 10,935 S-wave onsets of natural earthquakes observed by 45 seismic stations, and 3,121 P-wave onsets generated by artificial explosions. An anomalous zone of low S-wave velocity is discriminated at depths deeper than 12 km below the center of the Aira caldera. The S wave velocity is 18-55 % lower than the surrounding area. The volume of the anomalous zone is 139～255 km³ at shallower depths than 15 km, and the anomalous zone includes about 7 % melt (10～18 km³). Accumulation of magma in the anomalous zone activates a pressure source at the top of the zone, where velocity contrast of the S-wave is intense, and the pressure source induces inflationary ground deformation around the Aira caldera.