5:15 PM - 6:45 PM
[HDS08-P08] Drone magnetic survey for geothermal alteration areas to evaluate the risk of slope failure
Keywords:drone magnetic survey, hydrothermal alteration, clay, Yoshioka area, Aso volcano, risk of slope failure
Aeromagnetic surveys can be applied to map hydrothermal alteration areas to evaluate the risks of slope failure of volcanoes as clay minerals caused by the hydrothermal alteration show low magnetization. A case study in the western flank of central cones of Aso volcano was conducted using high-resolution aeromagnetic data obtained by Ministry of Land, Infrastructure, Transportation and Tourism in 2014. According to 3D magnetic imaging of the study area, magnetization lows are dominant in three fumarole and hot spring areas, Yunotani, Yoshioka and Jigoku-Tarutama, showing a capability of mapping of hydrothermal areas.
Based on the case study, an ultra-high resolution aeromagnetic survey using a multicopter (DJI Matrice 600 Pro) was conducted in March 2023 in the Yoshioka area, one of the three fumarole and hot spring areas above to clarify the detail relationship between the magnetic structure and hydrothermal alterations. While flying, an airborne magnetometer (Geometrics MagArrow) was suspended 3 m below the multicopter to keep away from the magnetic noise caused by the drone. MagArrow has been developed mainly for drones and is very light (1 kg) and 1 meter in length with a flat shape and can measure magnetic field at 1 kHz. The survey was successfully flown with narrow flightline spacing of 25 m and low flying altitude of 25 m above ground. Data processing of the observed magnetic data were conducted using the data processing software developed by the Geological Survey of Japan, AIST (Nakatsuka, 2016). Magnetic anomalies were, then reduced to the smoothed observation surface, assuming equivalent anomalies below the observation surface. According to the compiled magnetic anomaly map, a broad magnetic low occupies a U-shaped valley edged by the cliffs on which the Nagano ranch lies and corresponds to the fumarole and hot spring area. Magnetic highs lie along the cliffs and correspond to the outcrops of the Kusasenrigahama welded tuffs. As the magnetic anomalies seem to be affected strongly by topographic undulations, terrain-correction was applied to the observed total magnetic intensity anomalies and then reduction to the pole anomalies were calculated from the terrain-corrected anomalies. According to the reduction to the pole anomalies, magnetic highs were also distributed along the cliffs and some perturbations of magnetic anomalies were observed over the plateau with a gentle slope on the cliffs. In this presentation, the result of 3D magnetic imaging of the study area will be discussed by a comparison with a distribution of hydrothermal alteration areas.
Based on the case study, an ultra-high resolution aeromagnetic survey using a multicopter (DJI Matrice 600 Pro) was conducted in March 2023 in the Yoshioka area, one of the three fumarole and hot spring areas above to clarify the detail relationship between the magnetic structure and hydrothermal alterations. While flying, an airborne magnetometer (Geometrics MagArrow) was suspended 3 m below the multicopter to keep away from the magnetic noise caused by the drone. MagArrow has been developed mainly for drones and is very light (1 kg) and 1 meter in length with a flat shape and can measure magnetic field at 1 kHz. The survey was successfully flown with narrow flightline spacing of 25 m and low flying altitude of 25 m above ground. Data processing of the observed magnetic data were conducted using the data processing software developed by the Geological Survey of Japan, AIST (Nakatsuka, 2016). Magnetic anomalies were, then reduced to the smoothed observation surface, assuming equivalent anomalies below the observation surface. According to the compiled magnetic anomaly map, a broad magnetic low occupies a U-shaped valley edged by the cliffs on which the Nagano ranch lies and corresponds to the fumarole and hot spring area. Magnetic highs lie along the cliffs and correspond to the outcrops of the Kusasenrigahama welded tuffs. As the magnetic anomalies seem to be affected strongly by topographic undulations, terrain-correction was applied to the observed total magnetic intensity anomalies and then reduction to the pole anomalies were calculated from the terrain-corrected anomalies. According to the reduction to the pole anomalies, magnetic highs were also distributed along the cliffs and some perturbations of magnetic anomalies were observed over the plateau with a gentle slope on the cliffs. In this presentation, the result of 3D magnetic imaging of the study area will be discussed by a comparison with a distribution of hydrothermal alteration areas.