[S-VC35] Hydrothermal systems of volcanoes

[SVC35-P02] Examination of the causes of geomagnetic changes observed during periods of volcanic unrest based on numerical modeling

*Wataru Kanda¹, shunki tamura^2,3 (1.Multidisciplinary Resilience Research Center, Institute of Integrated Research, Institute of Science Tokyo, 2.Division of Earth and Planetary Sciences, School of Science, Tokyo Institute of Technology, 3.Unito Inc.)

Keywords:geomagnetic field changes, magnetization structure, thermal demagnetization, andesite

Geomagnetic observations around the active craters of volcanoes provide information on the underground thermal conditions, which is extremely useful for understanding volcanic activity. This aims to measure changes in the magnetization structure inside the volcanic edifice caused by the heat supply from the deep as geomagnetic changes. However, when continuous observations are performed, there are cases where geomagnetic changes remain unchanged, even though other mechanical observations indicate increased activity or are observed at a different time from the increased activity. For example, at the Kusatsu-Shirane Volcano, ground deformation suggesting underground inflation was continuously monitored in association with increased seismic activity since March 2014. However, geomagnetic changes were observed only for a short period in May 2014. In this study, we numerically examined the difference in the timing of activity from the perspective of changes in the magnetization structure around the assumed source of ground deformation. As a result, it was found that in volcanoes composed of weakly magnetized andesitic rocks, such as the Kusatsu-Shirane Volcano, even if thermal demagnetization occurs, no changes can be observed depending on the depth at which it occurs, and that the speed of change differs depending on whether demagnetization is caused by thermal conduction of the rocks or advective heat transfer due to high-temperature fluids.