Ground deformation in and around Jigokudani valley, Tateyama volcano, Japan, during the period of 2021-2022 revealed from combined data of leveling surveys and GPS observations

Abstract

Abstract Ground deformation in and around Jigokudani valley during the period from September 2021 through September 2022 detected from leveling surveys and GPS observations was modeled to interpret what occurred beneath the Jigokudani valley accompanied by volcanic activities. Most leveling benchmarks showed uplift of up to 0.9 cm during the one-year period. Some benchmarks located west part of Jigokudani valley showed subsidence. Two GPS stations in the valley also showed uplift up to 1.4 cm. These two GPS stations showed horizontal displacements up to 1.6 cm. The GPS station locates out of fumarolic areas of the valley showed very small displacement. A dislocation source was applied to the deformation. Assuming a Poisson’s ratio of 0.45, the optimal parameters were searched using Adam. A crack with a length of 348 m, a width of 1.4 m and a dip of 86.7° is located at a depth of 6.8 m near Koya jigoku and the new fumarolic area, which has recently become highly activated. The strike of the crack is N239°E. The opening of the crack of 36.2 cm yields a volume increase of 173 m3. The obtained crack is considered to correspond to the shallow aquifer, and the aquifer pushed out by hot volcanic gas and generated water vapor. Further investigation, such as seismic prospecting, is needed to confirm the result and interpretation of the present study. Although overall deformation can be broadly explained by opening of the crack, there is some differences between observation and calculation probably because actual shape of the crack is more complex. In addition, it is necessary to construct a unified model, combining not only geodetic data but also other data such as seismic prospecting as raised above.