5:15 PM - 6:30 PM
[SVC28-P10] Three-Dimensional Crustal Structure beneath Hachijojima Island using dense seismic observation data
Keywords:natural earthquake tomography, velocity structure, dense seismic observation, Hachijojima Island
Hachijojima Island is a volcanic island belonging to the Izu Islands, and in 2002, a volcanic earthquake swarm and a crustal movement were observed. Because of these volcanic activity, Hachijojima Island has been monitored by JMA. In order to interpret volcanic activity correctly, it is effective to understand the underground structure of the volcano by means of geophysical method.
Hagiwara and Watanabe (2019) have estimated the underground structure beneath Hachijojima Island from earthquakes data observed by permanent stations. In this study, in order to estimate the underground structure of Hachijojima Island in more detail, we installed 46 stations of 1Hz velocity seismograph (LE-3Dlite) on Hachijojima Island and Hachijo-kojima Island and conducted temporary seismic observation from September 2019 to March 2020 (182 days). We have picked P-wave and S-wave first arrivals manually on the seismic waveform data processing system, WIN system (Urabe and Tsukada, 1992), and the hypocenter determination by hypocenter determination program hypomh (Hirata and Matsu'ura, 1987).
We used the tomography program, SIMULPS12 (Evans et. al., 1994) to estimate the underground velocity structure. As a result of 3D analysis, we found that the high Vp anomaly at the depth of 2-5km just beneath Nishiyama. In particular, P-wave velocity structure was estimated with high resolution up to the depth of 4km. We compared our results with previous studies and discussed the validity of the analysis results and the effect of dense seismic observation on the resolution.
Hagiwara and Watanabe (2019) have estimated the underground structure beneath Hachijojima Island from earthquakes data observed by permanent stations. In this study, in order to estimate the underground structure of Hachijojima Island in more detail, we installed 46 stations of 1Hz velocity seismograph (LE-3Dlite) on Hachijojima Island and Hachijo-kojima Island and conducted temporary seismic observation from September 2019 to March 2020 (182 days). We have picked P-wave and S-wave first arrivals manually on the seismic waveform data processing system, WIN system (Urabe and Tsukada, 1992), and the hypocenter determination by hypocenter determination program hypomh (Hirata and Matsu'ura, 1987).
We used the tomography program, SIMULPS12 (Evans et. al., 1994) to estimate the underground velocity structure. As a result of 3D analysis, we found that the high Vp anomaly at the depth of 2-5km just beneath Nishiyama. In particular, P-wave velocity structure was estimated with high resolution up to the depth of 4km. We compared our results with previous studies and discussed the validity of the analysis results and the effect of dense seismic observation on the resolution.