[H-TT17] New Developments in Shallow Geophysics

[HTT17-09] Differential tomography of continuously repeated measurement data using electrical exploration method - Application to monitor changes in soil moisture content due to rainfall

*Ryota Watatani¹, Koichi Suzuki² (1.Cooperative Program for Resources Engineering, Graduate School of Engineering, Hokkaido University, 2.Research Group of Geoenvironmental Engineering, Division of Sustainable Resource Engineering, Faculty of Engineering, Hokkaido University)

Keywords:electrical exploration, differential tomography, RMS residual

Slopes at risk of large-scale landslides should be evaluated across the entire slope for the behavior toward groundwater infiltration from heavy rainfall. It is imperative to establish monitoring techniques to visualize rainwater infiltration across the entire slope for the long-term risk management of landslides. However, it is difficult to quantitatively evaluate the saturation rate change caused by rainwater infiltration using only the electrical exploration data. Suzuki et al. (2018) estimated the porosity and saturation rate sections by combining the S-wave velocity and resistivity based on an unconsolidated sand model (Avseth, 2005). In this study, differential tomography by Sugimoto (1995) was performed on the electrical exploration data measured repeatedly on the slope formed on the Joso Plateau, and the cross section of the resistivity change rate was obtained. In addition, by combining the S-wave velocity structures obtained by surface wave exploration conducted on the same survey line, the cross-section of the rate of change in saturation due to precipitation infiltration was estimated according to the analysis flow shown by Suzuki et al. (2018). Hence, the differential tomography result had a smaller RMS residual than the conventional method and was consistent with the geological structure. In the cross-section of the rate of change in saturation, saturation increased from the ground surface and a region where the saturation decreased appeared below it; a minor change in saturation was observed in the region below the clayey layer.

REFERENCES
Avseth, P., Mukerji, T. and Mavko, G. Quantitative seismic interpretation, Cambridge University Press, 2005.
Sugimoto, Y., Proceeding of the SEGJ Conference 92, 57-62, 1995. (in Japanese)
Suzuki, K. et.al., BTSURI-TANSA, 69(2), 103-116, 2016. (in Japanese)
Suzuki, K. et.al., BTSURI-TANSA, 71, 1-14, 2018. (in Japanese)