Twin sources of high-frequency volcanic tremor of Izu-Oshima Volcano, Japan

The 1986 fissure eruption of Izu-Oshima volcano was preceded and followed by strong volcanic tremor activities. The post-eruption tremor activity consists of an alternating sequence of a tremor episode lasting about 10 min and the subsequent quiescence of about 40-50 min. The authors observed this post-eruption activity by a 24-channel seismic array deployed on the caldera floor. The semblance analysis of the recorded data revealed that high frequency (>5 Hz) components of the tremor were radiated from two separated sources beneath the caldera. The tremor first occurred at one source and then migrated to the other source in a transition time of about a few minutes during each tremor episode. This transition suggests that the two sources are dynamically linked with each other in a magma-filled crack or conduit.