AN AUDIO-FREQUENCY MAGNETOTELLURIC SURVEY AROUND THE CRATERS OF THE 2018 ERUPTION AT MT. MOTOSHIRANE, JAPAN

In 2018, a phreatic eruption occurred from the Kagami-ike-kita crater of Mt. Motoshirane in central Japan. Mt. Motoshirane is one of the pyroclastic cone groups of Kusatsu-Shirane volcano. Since most of the volcanic activities had occurred on the other pyroclastic cone group, few studies were conducted at Mt. Motoshirane. In this study, we report a three-dimensional resistivity structure around the craters that erupted in 2018 to clarify the shallow hydrothermal system of Mt. Motoshirane. For this purpose, we conducted an audio-frequency magnetotelluric survey around the 2018 craters in 2020. A three-dimensional resistivity structure model was constructed using an inversion code utilizing tetrahedral meshes to express the steep topography around the surveyed area. The obtained model was characterized by features similar to the apparent resistivity distribution: high resistivities near the surface and low resistivities in the deep. In the presentation, we showed the inferred shallow structure of Mt. Motoshirane and give an interpretation based on the previous studies.