17:15 〜 19:15
[SEM15-P08] 桜島火山噴火時に記録された地磁気地電流データのパルス状変動に関する初期解析結果
キーワード：噴火に伴う地磁気地電流パルス、桜島火山
Sakurajim, an andesite-dacite composite volcano of approximately 80km² in land area, is a post-caldera volcano on the southern rim of the Aira caldera. This caldera was formed by a massive eruption of roughly 29 ka, making it 22 kilometers in diameter and 200 meters deep in Kagoshima/Kinkowan Bay. Additionally, Sakurajima volcano is a prominent feature of the dense Quaternary volcanic edifices along the N30°E–S30°W volcanic front associated with the subduction of the Philippine Sea Plate, which characterizes the island of Kyushu, the southernmost and third-largest of Japan's four main islands. According to a report by the Japan Meteorological Agency, Sakurajima has experienced between 99 and 1,252 eruptions (explosions or eruptions of a particular scale or larger) per year over the last 10 years, up to 2024. Sakurajima volcano consists of three peaks: Kita-dake at 1,117m above sea level, Naka-dake at 1,060m above sea level, and Minami-dake at 1,040m above sea level, with Minami-dake having two active craters (Showa Crater, located near the 8th station on the eastern slope of Minami-dake, and Minami-dake Summit Crater). These craters alternate in eruptive activity, and the Minami-dake Summit Crater is particularly active as of 2025.
From October 2024 to February 2025, we conducted broadband Magnetotelluric (MT) surveys of 35 sites, 17 sites of full-component MT (magnetic and electric fields) and 18 sites of two-component MT (electric field), distributed throughout all accessible areas of Sakurajima. Even during this observation period, Sakurajima experienced more than 150 eruptions, including the eruption on December 23, 2024, when volcanic ash and smoke rose to 3,400 meters above the summit crater. The primary purpose of the surveys is to elucidate subsurface heterogeneity beneath Sakurajima Volcano. In this study, however, we focus on comparative investigations of the correlations between syn-eruption pulse-like variations in the MT data and volcanic phenomena. Several geoelectromagnetic studies have reported coupling between electromagnetic field changes and seismic motion, as well as between electromagnetic field fluctuations and infrasound (an acoustic wave propagating through the air) [e.g., Mogi et al., 2000; Aizawa et al., 2010]. On the other hand, there are still uncertainties regarding the correlation between the eruption phenomena and the recorded electromagnetic field variations. Sakurajima volcano is one of the most well-monitored active volcanoes in Japan. Therefore, multiparametric observations, including geophysical observations such as seismic motion, ground deformation, and infrasound (an acoustic wave propagating through the air), are acquired in and around Sakurajima to monitor volcanic activity. Therefore, we investigated the MT, infrasound, and seismic motion data in order to clarify the correlation between syn-eruption pulse-like fluctuations in the MT data and volcanic phenomena.
From October 2024 to February 2025, we conducted broadband Magnetotelluric (MT) surveys of 35 sites, 17 sites of full-component MT (magnetic and electric fields) and 18 sites of two-component MT (electric field), distributed throughout all accessible areas of Sakurajima. Even during this observation period, Sakurajima experienced more than 150 eruptions, including the eruption on December 23, 2024, when volcanic ash and smoke rose to 3,400 meters above the summit crater. The primary purpose of the surveys is to elucidate subsurface heterogeneity beneath Sakurajima Volcano. In this study, however, we focus on comparative investigations of the correlations between syn-eruption pulse-like variations in the MT data and volcanic phenomena. Several geoelectromagnetic studies have reported coupling between electromagnetic field changes and seismic motion, as well as between electromagnetic field fluctuations and infrasound (an acoustic wave propagating through the air) [e.g., Mogi et al., 2000; Aizawa et al., 2010]. On the other hand, there are still uncertainties regarding the correlation between the eruption phenomena and the recorded electromagnetic field variations. Sakurajima volcano is one of the most well-monitored active volcanoes in Japan. Therefore, multiparametric observations, including geophysical observations such as seismic motion, ground deformation, and infrasound (an acoustic wave propagating through the air), are acquired in and around Sakurajima to monitor volcanic activity. Therefore, we investigated the MT, infrasound, and seismic motion data in order to clarify the correlation between syn-eruption pulse-like fluctuations in the MT data and volcanic phenomena.