GNSS観測による姶良カルデラ下へのマグマ供給率の推定

Abstract

We applied a composite analysis of spherical pressure source at around Aira caldera, Kyushu Japan. Horizontal displacements obtained from GNSS observations and vertical displacements from leveling survey, during 2017 to 2019, were used for the analysis. A volume increase source of 15.2 × 10⁶ m³ was estimated at a depth of 11.2 km near the central part of Aira Caldera. The volume change during the last 10 years was calculated based on the location of the source and change in horizontal distance of a baseline which crosses the central part of Aira caldera. The amount of magma supplied to Aira caldera was estimated by adding the amount of volcanic ash ejected from Sakurajima volcano, to volume change of pressure source. Estimated magma supply during the last 10 years are 70 × 10⁶ m³ and 93 × 10⁶ m³, respectively, assuming equivalent densities of 2.5 g/cm³ and 1.0 g/cm³. The average magma supply rate is close to the 10 × 10⁶ m³/yr obtained in previous studies. This suggests that the magma reservoir beneath Aira caldera has been stable for a long period and magma supply to the reservoir has continued up to the present.