Near surface geophysics

[NS-04] Mapping aquifer storage properties using S-wave velocity and InSAR measurements in the Kumamoto area, Japan

*Mohamed Mourad^1,2, Takeshi Tsuji^1,3, Tatsunori Ikeda^1,3, Kazuya Ishitsuka⁴, Shigeki Senna⁵ (1. Department of Earth Resources Engineering, Kyushu University. (Japan), 2. Department of Geology, Faculty of Science, Fayoum University. (Egypt), 3. International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University. (Japan), 4. Department of Urban Management, Kyoto University. (Japan), 5. National Research Institute for Earth Science and Disaster Resilience. (Japan))

Aquifer parameters such as storage coefficient (SK) are crucial for developing sustainable water management strategies for the incoming decades. In this work, 3D S-wave velocity (Vs), InSAR deformation, and groundwater level data were used to construct the relationship between SK of the confined aquifer and Vs (SK-Vs relationship) for mapping SK in the Kumamoto area, Japan. Specifically, we constructed the 3D Vs model from 1D Vs structures by miniature array analysis of microtremors conducted at 676 measured points. The part of faulted/fractured zones could be identified as low Vs zones in the 3D model. We also used time series of InSAR deformation and groundwater level data at 13 well sites covering a period between April 2016 and September 2018 for characterizing SK of the confined aquifer. The resulting SK agreed with typical values in semiconfined and confined conditions. From the estimated SK and Vs around the corresponding well locations, we found an empirical relationship between SK and Vs which indicates compressibility of aquifer is related to stiffness and Vs. By applying the SK-Vs relationship for the 3D Vs model, we mapped SK in the study area, filling spatial gaps in the existing aquifer storage properties data. There is a good correlation between the estimated SK and hydrogeological setting: semi confined conditions are indicated from high SK values in the south western part, where the discontinuity of impermeable clay layer of lacustrine sediments could be underlying in the deep aquifer. Thus, our approach is effective to estimate aquifer storage properties from Vs even where limited groundwater level data are available.