Ground strains induced by the 2022 Hunga-Tonga volcanic eruption, observed by a 1500-m laser strainmeter in Kamioka, Japan

Abstract

Abstract In this study, we detected the horizontal ground strains, induced by the atmospheric Lamb wave emitted from the 2022 eruption of the Tong–Hunga Ha’apai undersea volcano, at an underground observatory in Kamioka, Japan. The observed strains were in the range of 10-11 to 10-10 and precisely measured using a 1500-m laser strainmeter with a high resolution of the order of 10-12. The strainmeter was constructed in a tunnel of KAGRA gravitational-wave telescope. Our observations showed that strain and atmospheric pressure were clearly correlated, resulting in a regression coefficient of -(2.3 –3.7) × 10-10 strain/hPa. This finding was compared with the responses under regular pressure conditions and the estimations by the local deformation model and the traveling wave model. The observed coefficients for the Lamb wave had smaller magnitudes than those under regular conditions and has a value between that of the two theoretical models. These results reflect the intermediate scale of pressure distribution of the Lamb wave between the assumptions of the simple models. The strain variations were also found to have started earlier than the corresponding pressure changes at the observation site with a characteristic time shifts ranging in 25–155 seconds. This finding indicates that the remote pressure loading caused the ground strains, and such interpretation was enabled by the specific pressure distribution of the Lamb wave.