5:15 PM - 6:30 PM
[SVC28-P16] Vault-housed extensometers and tiltmeters recorded continuous crustal movement during the eruption of Kirishima Shinmoe-dake in 2018
Keywords:Shinmoe-dake, Extensometers, Tiltmeter, Ground deformation
Shinmoe-dake is one of the volcanoes constituting the Kirishima volcanic group in southern Kyushu, and it is an active volcano with major eruptions in 2011 and 2018 in recent years. In this study, we use vault-housed extensometer and tiltmeter data to analyze the ground deformation recorded during the Shinmoe-dake eruption in 2018. The purpose of this study is to clarify what occurred underground during the eruption with high spatial and temporal resolution.
We used the vault-housed extensometer data installed at the Isa Observatory (ISA), Kyoto University. The ISA consists of tunnels in three directions, E1, E2, and E3. Each extensometer made up of 30m lengths of super-invar rods. E1 extends in the direction of the presumed contraction source of the 2018 eruption, and E2 in the direction orthogonal to E1. The tiltmeter data were obtained from three stations: Takachihokawara (KITK) station of the Japan Meteorological Agency (JMA), Hinamoridai (KRHV) station and Manzen (KRMV) station of the National Research Institute for Earth Science and Disaster Resilience (NIED). We resampled the original data at 1 hour by simple averaging and removed tidal components from the original time series using the tidal analysis software BAYTAP-G (Ishiguro et al., 1984). According to the Japan Meteorological Agency (JMA), the deep point source of the 2018 eruption contracted at the beginning of March, and we focused this period and compared each data and arranged its character.
The tilt at the KITK and the KRHV started to change around 9:00 a.m. on March 6, while the strain at Isa and the tilt at KRMV started to change in the morning of March 5. New lava was found in the crater on March 6, and the changes in Isa and KRMV were detected earlier than that. Strain variations in ISA were characterized by an extension in the E1 component and by contraction in the E2 component, which can be interpreted as the contraction of the pressure source estimated by the JMA to be located about 6 km northwest of Shinmoe-dake. In addition, the tilt in KRMV changed in the direction of subsidence from north to northeast until 9:00 a.m. on the 6th, and the strain rate in ISA also changed after 9:00 a.m. on the 6th.
In summary, we think that the first contraction occurred at depth on the morning of the March 5th, before new lava was found in the crater, and the second contraction occurred at a shallower depth on the northeast side during the 2018 eruption.
We used the vault-housed extensometer data installed at the Isa Observatory (ISA), Kyoto University. The ISA consists of tunnels in three directions, E1, E2, and E3. Each extensometer made up of 30m lengths of super-invar rods. E1 extends in the direction of the presumed contraction source of the 2018 eruption, and E2 in the direction orthogonal to E1. The tiltmeter data were obtained from three stations: Takachihokawara (KITK) station of the Japan Meteorological Agency (JMA), Hinamoridai (KRHV) station and Manzen (KRMV) station of the National Research Institute for Earth Science and Disaster Resilience (NIED). We resampled the original data at 1 hour by simple averaging and removed tidal components from the original time series using the tidal analysis software BAYTAP-G (Ishiguro et al., 1984). According to the Japan Meteorological Agency (JMA), the deep point source of the 2018 eruption contracted at the beginning of March, and we focused this period and compared each data and arranged its character.
The tilt at the KITK and the KRHV started to change around 9:00 a.m. on March 6, while the strain at Isa and the tilt at KRMV started to change in the morning of March 5. New lava was found in the crater on March 6, and the changes in Isa and KRMV were detected earlier than that. Strain variations in ISA were characterized by an extension in the E1 component and by contraction in the E2 component, which can be interpreted as the contraction of the pressure source estimated by the JMA to be located about 6 km northwest of Shinmoe-dake. In addition, the tilt in KRMV changed in the direction of subsidence from north to northeast until 9:00 a.m. on the 6th, and the strain rate in ISA also changed after 9:00 a.m. on the 6th.
In summary, we think that the first contraction occurred at depth on the morning of the March 5th, before new lava was found in the crater, and the second contraction occurred at a shallower depth on the northeast side during the 2018 eruption.