[M-TT45] Brand-new scope of coupling geophysics being established by infrasound and associated waves

[MTT45-P01] Short-term gravity changes observed in and around Kussharo Caldera, Eastern Hokkaido, Japan

★Invited Papers

*Kazunari Nawa¹, Yuichi Imanishi², Hiroshi Ikeda³, Ryo Honda⁴, Daisuke Oka⁵, Tatsuo Shirakawa⁶, Takuma Oi⁷, Hiroaki Takahashi⁸, Mako Ohzono⁸, Hiroshi Aoyama⁸, Kazumi Okada⁸, Teruhiro Yamaguchi⁸ (1.National Institute of Advanced Industrial Science and Technology, 2.ERI, Univ. Tokyo, 3.KEK, 4.MFRI, 5.HRO, 6.Kitami Inst. Tech., 7.Toho Mercantile Co., 8.Hokkaido Univ.)

We aim to detect changes in gravity due to subsurface magmatic activity, fault movement, and related changes in physical properties and crustal deformation around the Kussharo caldera by using an effective combination of a superconducting gravimeter which enables long-term stable observations, an absolute gravimeter which is drift-free, and a spring-type relative gravimeter which is portable and capable of continuous measurements. Continuous observation by iGrav superconducting gravimeter was started at Teshikaga Observatory, Hokkaido University in November 2018. As a result, seasonal changes in gravity were detected, mainly caused by changes in the mass of land water such as soil moisture and snow cover. However, the residual gravity time series after land water corrections indicated short-term changes other than hydrological signals. Possible sources of these short-term gravity changes include the effects of near- and far-field earthquakes, and ground vibrations caused by pressure fluctuations and/or lake water level changes. To investigate the causes of these changes, we have additionally installed field observations, such as a relative gravity meter deployed in the Kussharo caldera area, water pressure (water level) meters installed in Lake Kussharo, a microbarometer and a snow load gauge installed at the Teshikaga Observatory. We will present results of comparison of the data from these new observations with the gravity changes from the superconducting gravimeter.