11:30 AM - 11:45 AM
[STT49-04] Study on the extracting dangerous area for shallow landslides in the Nachi River basin using the airborne electromagnetic survey
Keywords:Airborne electromagnetic survey, Shallow landslide, Boring survey
As features of the airborne electromagnetic survey, it is possible to estimate the vertical change of the underground geological structure, and can estimate the height of the groundwater level. Therefore, in this research, we conducted the airborne electromagnetic survey in 2012 in the Nachi River Basin (13.4km2). Then, from 2016, in order to verify the results of the airborne electromagnetic survey, we chose two points where longitudinal distribution of resistivity value is greatly different and conduct the boring survey and investigate the change of the groundwater level. We examined the difference in the resistivity distribution between where it is easy to collapse and where it is not likely to collapse.
From this study, it is pointed out that the area where the resistivity value greatly changes is distributed in the basement as a feature of the collapsible slopes in the Nachi River basin. In the case of the Nachi River basin, these areas are presumed to be the geological boundary between granite porphyry (Kumano acidic rocks) and sedimentary rock (Kumano group). Depending on the direction and the angle of the geological boundary, the sedimentary rock has a property that it is difficult for water to pass through, so the flow of water on the slope is hindered and the slope may collapse. For this reason, it was suggested that the underground geological structure has a great influence on the flow of water, and the risk of the shallow landslide is influenced.