[SVC45-28] Recent seismic activities at Miyake-jima volcano
Keywords:volcanic earthquakes, volcanic activity, Miyake-jima volcano
From relocated hypocenters, we can find out the following features in the present seismicity in Miyake-jima;
1. Almost all earthquakes concentrate at the region beneath southern part of the summit crater from the ground surface to the depth of 3km below sea level. Earthquakes are classified as BH, BL and A types from the point of the features in waveforms.
2. More than 50% of the events are classified as BL type, more than 20% as A type, and less than 20% as BH type.
3. Focal depths of BL type earthquakes are shallower than 1km below sea level. On the other hand, those of A type are greater than the depth. The boundary of their distributions are very sharp. The focal depths of BH are concentrated very shallow and partly overwrapped with those of BL type.
4. The distribution boundary of BL and A types agree with the depth where high resistivity zone changes to low resistivity zone inferred from MT survey carried out 2012.
5. In addition, epicenters of A type linearly extends to southwestward to the point 2km far from the summit crater. It is the “node point” where direction of dike intrusions changed from south-westward to north-westward in the first stage of 2000 eruption, and might be also the center of sources of VLP events occurring just before the summit collapse in August 2000.
In the 2000 eruption, the “node point” might play important role, but detailed process is still unsolved. From the present seismic activity, the “node point” is still alive and may play important role again in future eruption.
In this study, we grateful to JMA, NIED and Tokyo Metropolitan Government for providing data. This research is partly supported by Integrate Program for Next Generation Volcano Research and Human Resource Development sponsored by MEXT.