16:00 〜 16:15
[STT34-03] 無人ヘリコプターによる草津白根山空中磁気測量
Kusatsu-Shirane volcano is one of the active volcanoes in Japan, and phreatic explosions have occurred in Mt. Shirane in 1983 and most recently, Mt. Motoshirane in 2018. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur.
Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data of high spatial resolution to map the magnetic anomaly and infer the magnetization intensity structure in the region, just after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously-driven-model that can fly along a programmed course. The flight height above the ground and a measurement line spacing were set to ~150 m and ~100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~1000 nT peak-to-peak.
The estimated magnetization intensity structure derived from measured data showed a magnetized surface layer with a normal polarity of a few hundred meters thick, composed of volcanic deposits of recent activities. Underneath, a structure with reverse-polarity magnetization was found. This probably corresponds to the Takai lava flow in the Early Quaternary period (~1 Ma) to which, it is believed that the basement rock of this region can be dated back to. Just beneath the crater lake of Mt. Shirane (Yugama) and Mt. Motoshirane, normally magnetized structures were inferred even at 1500 m depth from the surface. This may have been caused by the replacement of old lava with a new one because of frequent repetition of volcanic events which occurred through the two main pathways.
Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data of high spatial resolution to map the magnetic anomaly and infer the magnetization intensity structure in the region, just after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously-driven-model that can fly along a programmed course. The flight height above the ground and a measurement line spacing were set to ~150 m and ~100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~1000 nT peak-to-peak.
The estimated magnetization intensity structure derived from measured data showed a magnetized surface layer with a normal polarity of a few hundred meters thick, composed of volcanic deposits of recent activities. Underneath, a structure with reverse-polarity magnetization was found. This probably corresponds to the Takai lava flow in the Early Quaternary period (~1 Ma) to which, it is believed that the basement rock of this region can be dated back to. Just beneath the crater lake of Mt. Shirane (Yugama) and Mt. Motoshirane, normally magnetized structures were inferred even at 1500 m depth from the surface. This may have been caused by the replacement of old lava with a new one because of frequent repetition of volcanic events which occurred through the two main pathways.