11:00 〜 13:00
[MTT45-P06] 伊豆諸島の火山観測網で捉えられた火球シグナル
キーワード：火球、空振、衝撃波
Infrasound induced by falls of fireballs are occasionally recorded by microphones, barometers, and seismometers located at volcanic observation stations. The fireball signals are possibly misunderstood as signals generated by volcanic activities such as opening vent and emission of volcanic gas and rocks. Also, they may cause errors for determining source locations of volcanic earthquakes, so that understanding the characteristics is required to distinguish them from volcanic signals. On the other hand, if fall of a fireball generates atmosphere-to-ground signal near volcanoes, the data are useful as references to identify volcanic infrasound in the method proposed by Kurokawa and Ichihara (2020).
Based on the background, we analyzed two fireballs fallen on July 2 (FB1) and August 21 (FB2) in 2020. The both fireballs were observed in skies over a wide stretch of Japan. FB1 meteorite registered as “Narashino” in the Meteoritical Bulletin Database (Gattacceca et al., 2021), hit Japan and landed on a condominium in Chiba prefecture, while FB2 meteorite was burned up in the atmosphere and/or fell in the ocean (Fujii, 2020). We investigate the seismic and infrasonic characteristics of the signals recorded by volcano observation networks along Izu Islands by reference to the trajectories estimated by M. Yamada (2020). One of the unique characteristics found in the seismic signals is the amplitude, which does not decay with distance from the trajectory but increases with the distance on both Izu-Oshima and Miyakejima in the case of FB2, while the infrasonic data recorded shock wave signals as a shape of “N” at all stations. In this presentation, the characteristic of seismic amplitude is discussed and compared with the site amplification factors (Ogiso et al., 2015). We also confirmed that FB1 and FB2 signals show clear infrasonic patterns in the cross-correlation analysis (Ichihara et al., 2012), and ranges of the spectral amplitude ratios between seismic records and infrasonic records are included in the observed values for atmosphere-to-ground signals, 0.1-10 μm s-1/Pa, from various sources like volcanoes (Nishida and Ichihara, 2015; Ichihara 2016; Matoza and Fee 2014) and thunder (Lin and Langston 2007, 2009).
Based on the background, we analyzed two fireballs fallen on July 2 (FB1) and August 21 (FB2) in 2020. The both fireballs were observed in skies over a wide stretch of Japan. FB1 meteorite registered as “Narashino” in the Meteoritical Bulletin Database (Gattacceca et al., 2021), hit Japan and landed on a condominium in Chiba prefecture, while FB2 meteorite was burned up in the atmosphere and/or fell in the ocean (Fujii, 2020). We investigate the seismic and infrasonic characteristics of the signals recorded by volcano observation networks along Izu Islands by reference to the trajectories estimated by M. Yamada (2020). One of the unique characteristics found in the seismic signals is the amplitude, which does not decay with distance from the trajectory but increases with the distance on both Izu-Oshima and Miyakejima in the case of FB2, while the infrasonic data recorded shock wave signals as a shape of “N” at all stations. In this presentation, the characteristic of seismic amplitude is discussed and compared with the site amplification factors (Ogiso et al., 2015). We also confirmed that FB1 and FB2 signals show clear infrasonic patterns in the cross-correlation analysis (Ichihara et al., 2012), and ranges of the spectral amplitude ratios between seismic records and infrasonic records are included in the observed values for atmosphere-to-ground signals, 0.1-10 μm s-1/Pa, from various sources like volcanoes (Nishida and Ichihara, 2015; Ichihara 2016; Matoza and Fee 2014) and thunder (Lin and Langston 2007, 2009).