[S-EM12] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM12-06] Building the 3D model with the geophysical exploration measurements: A case example with the Choushui Alluvial fan in the Changhua area of Central Taiwan

★Invited Papers

*CHANG PINGYU¹、Jordi Mahardika Puntu¹、Jun-Ru Zheng¹、Lingerew Nebere Kassie¹、Ding-Jiun Lin¹、Haiyina Hasbia Amania¹ (1.Department of Earth Sciences, National Central University )

キーワード：3D resistivity model, Transient Electromagnetic Method (TEM), Vertical Electrical Resistivity, Magnetotelluric (MT) surveys, Borehole resistivity measurements

In this study, we utilized the Transient Electromagnetic Method (TEM), borehole resistivity measurements (NBR), as well as vertical electrical resistivity (VES) and Magnetotelluric (MT) surveys to construct a resistivity model in the Changhua region of the Choushui River alluvial fan in Central Taiwan. The objective was to develop a shallow resistivity model for the region, serving as a valuable correlation tool for future hydrogeological model establishment. We applied the maximum-minimum normalization method to the corresponding resistivity measurements for data assimilation and calibration. This process aligned the normalized values of each corresponding cluster. Following the assimilation, we employed the Kriging method to spatially interpolate and extrapolate all normalized resistivity values, constructing a three-dimensional resistivity model for the alluvial fan area of the Choushui River. Upon comparing core records in the study area, we observed that the high-resistivity layers in the model corresponded roughly to layers dominated by gravel and sand, while layers mainly composed of mud at depths of 140-220 meters in the core records were consistent with low-resistivity layers in the model (approximately below 30 Ohm-m). Further analysis of a horizontal cross-section at a depth of 150 meters below sea level within the region revealed localized low-resistivity zones below 20 Ohm-m in the Sichou area. The distribution of this zone roughly corresponds to areas with faster subsidence rates in year from 2020 to 2021, indicating a certain correlation between the spatial distribution of localized low-resistivity muddy layers and severe subsidence areas in the Sichou region.