[DM-P-05] High-resolution velocity image beneath Hachijojima Island from dense seismic observation data
Hachijojima Island, one of the 50 active volcanoes that is continuously monitored its activity by Japan Meteorological Agency is located near the boundary between Pacific Plate and Philippine Sea Plate. There have been no eruptions since 1605, and volcanic activity has been relatively low in recent years. However, a volcanic earthquake swarm and a crustal movement were observed in 2002. In order to interpret volcanic activity correctly, it is essential to understand the subsurface structure beneath the volcano by means of geophysical method.
In this study, therefore, we have installed 46 stations of seismograph on Hachijojima Island and Hachijo-kojima Island and conducted temporary seismic observation from September 2019 to March 2020 (182 days) to image the velocity structure beneath Hachijojima Island in higher resolution.
We used the travel time tomography program, SIMULPS12 (Evans et. al., 1994) to estimate the velocity image from high density seismic data. As the results, we obtained high-resolution three-dimensional velocity image up to the depth of 8km just beneath Mt. Nishiyama. There are two high Vp anomalies at the depth of 2-5km just beneath Mt. Nishiyama. These anomalies are continuous from deeper area and could represent the detailed structure of dykes penetrated in 2002. We compared our results with previous studies, confirmed the validity of the analysis results and discussed the subsurface structure of Hachijojima Island.
In this study, therefore, we have installed 46 stations of seismograph on Hachijojima Island and Hachijo-kojima Island and conducted temporary seismic observation from September 2019 to March 2020 (182 days) to image the velocity structure beneath Hachijojima Island in higher resolution.
We used the travel time tomography program, SIMULPS12 (Evans et. al., 1994) to estimate the velocity image from high density seismic data. As the results, we obtained high-resolution three-dimensional velocity image up to the depth of 8km just beneath Mt. Nishiyama. There are two high Vp anomalies at the depth of 2-5km just beneath Mt. Nishiyama. These anomalies are continuous from deeper area and could represent the detailed structure of dykes penetrated in 2002. We compared our results with previous studies, confirmed the validity of the analysis results and discussed the subsurface structure of Hachijojima Island.
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