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. We 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 (>5Hz) 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. Copyright 1990 by the American Geophysical Union.