EXPLOSION SEISMIC STUDIES IN SOUTH KYUSHU ESPECIALLY AROUND THE SAKURAJIMA VOLCANO

A series of seismological observations of explosions from 1972 to 1977 has been worked out to study underground structure and possible anomaly of wave propagation beneath and around the Sakurajima Volcano and the Aira Caldera as well as regional structure of south Kyushu. Results described in this report are summarized as follows:1. Name, velocity and bottom depth of the identified layers are, L-1, 3.7-3.8km/sec, 0.7-1.8km; L-2, 4.7-4.9km/sec, 3.3-5.6km; L-3, 5.6-6.1km/sec, 22km; L-4, 7.0km/sec, (40km); L-5, (7.8km/sec).2. Two fan-shooting observations revealed following anomalies of wave propagation.1) A large attenuation of the amplitude of seismic waves occurs under the Sakurajima Volcano and the Aira Caldera.2) Wave velocity is likely to decrease under the Sakurajima Volcano.3) These anomalies of wave propagation occurs at the 6km/sec layer.