[A-HW25] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW25-P05] Integration of Multi-Method Resistivity Data for Building the 3D Subsurface Hydrogeological Model of an Alluvial Fan

*CHANG PINGYU¹ (1.National Central University, Taiwan)

Keywords:3D resistivity model, Data Integration, Land subsidence

This study integrates resistivity data obtained from various geophysical methods, including 64-inch well logging resistivity from observation wells, large-offset one-dimensional vertical electrical sounding (VES), and transient electromagnetic (TEM) surveys conducted by our team. After spatial resampling of the data, we used several data integration methods to classify the resistivity values obtained from different measurement methods, determining the optimal classification hierarchy and corresponding clusters. Each cluster underwent numerical normalization and feature scaling to establish a homogenized feature field suitable for spatial interpolation. Finally, by mapping the feature field to the target resistivity values of specific geophysical methods, we reconstructed an integrated three-dimensional resistivity distribution model. Following these assimilation steps, we developed a 3D resistivity model covering depths of up to 200 meters from the alluvial fan apex to its distal end. The distribution of resistivity values in the model reveals higher resistivity sediments near the eastern part of the study area, close to the fan apex, as well as in the southeastern region near the Beigang River. A preliminary comparison with borehole core data indicates that areas with resistivity values exceeding 130 Ohm-m are strongly correlated with gravel-dominated formations. This high-resistivity zone extends laterally from the fan apex toward the fan center, gradually tapering off in the mid-fan region. However, we also observed an isolated high-resistivity structure in the central part of the fan, which appears to be disconnected from the primary high-resistivity zone near the fan apex. Further comparison with the annual cumulative subsidence data in the Yunlin area reveals a strong spatial correlation between regions of significant subsidence and this isolated high-resistivity structure.