2017年の南岳爆発に前後する傾斜ひずみ変化

Abstract

Deformation source associated with each eruption at Sakurajima have been estimated beneath Minami-dake for each eruption. Deformation sources for mid-long term magma intrusion event were estimated beneath Aira caldera, Kita-dake and Minami-dake. A new observation tunnel was installed at Komen in August 2016. On November 13, 2017, an explosion with an infrasound occurred at Minami-dake at 22:07. Ground deflation was accompanied and kept for approximately five hours. Most tilt vectors showed radial pattern of deflation at Minami-dake, whereas that at Komen showed deflation at northern part of Sakurajima. We modeled the tilt and strain change except Komen. At first, we modeled the deflation based on the Mogi model. A deflation source was located beneath Minami-dake. Directions of observed and calculated tilt vectors were slightly different at western and northern stations. We then applied a sill model. A sill was located between Minami-dake and Kita-dake. Magma may migrate wider area than it has been considered during each eruption at Sakurajima. This sill model cannot explain tilt change at Komen. There might be a local displacement around Komen.