[SEM19-P04] Study on long-term variation of geoelectric field observation
Keywords:geoelectric field observation, electrical prospecting
Based on Morinaga and Toya (2015) and Fujii et al.(2007), we focus on geological structures around the electrode at the south end of the north-south line at Kakioka. We infer the geological structure from the distribution of the electrical resistivity.
The electrical prospecting was applied to an area of 20m x 20m with the south electrode as the center. Observations were conducted in March, May and October giving 7 observation lines around the south electrode, 2 lines around the east electrode, and 1 line around a boring hole (fig.1). Apparent resistivity was estimated from the observed currents and voltage differences.
We assume that the subsurface structure is one-dimensional and three layers are stratified. An optimal model of the resistivity distribution was obtained by inversion. All lines show a high resistivity layer at the surface followed by a low resistivity layer and then a high resistivity layer at the bottom. The thickness of the first layer is increased eastward from the south electrode.
The optimal model was compared with a boring profile obtained near the investigated area. We interpret that the resistive surface layer is permeable top soil and the second conductive layer is impermeable clay(Figure 2).We suspect that rain water flows on the top of clay to the east and the south electrode suffers from larger amount of water than the other electrodes.