LaCoste型相対重力計の重力連続観測で検出された2022年トンガ火山噴火の大気圧変動に伴う重力変化

抄録

　We detected the sub-microgal gravity change due to the air pressure change associated with the 15 January 2022 eruption of Hunga Tonga-Hunga Haʼapai volcano, by the continuous gravity observation using a spring-type portable relative gravimeter. We have been collecting the 1-Hz readout voltage value of the LaCoste & Romberg G31 gravimeter at the gravity measurement room in Kyoto University, along with the air pressure value using a MEMS pressure sensor. We obtained the time series of gravity residual on 15 January 2022, by correcting for the tidal gravity change in the gravity data which were converted from the original voltage data. We found that the gravity residual changed by approximately 0.5 and 1.2 μGal peak-to-peak in the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively, as the air pressure changed by approximately 2 hPa due to the propagation of the atmospheric Lamb waves generated by the Tonga volcanic eruption. The gravity changes can be explained by the the acoustic-gravity-wave theory within 0.1 μGal root-mean-square error, if the elastic parameters at the depths of 30 and 10 km of the PREM model were used in calculating the theoretical gravity changes for the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively.