The demand for groundwater resources has increased owing to global developments of urbanization, industry, and agriculture. There is thus a need for advanced geophysical techniques that can be used for accurate surveying of groundwater resources. Although electric sounding has been a standard technique in surveying, it is still difficult to specify the groundwater table and aquifer distribution accurately when considering only resistivity and induced polarization. The present paper aims to improve the accuracy by developing a variable-frequency-based electric sounding system that measures apparent resistivity in the frequency range of electrical current transmittance of 1–100 Hz at intervals of 1 Hz. Experiments using soil samples and an aquifer model based on a tank show that the coefficient of variation of resistivity (C_v) in the frequency range of 21–40 Hz was effective in detecting an aquifer because it was higher than coefficients in other frequency ranges. To verify the availability of this indicator, three field experiments with different geologic settings (i.e., plateau, coastal, and limestone aquifer fields located in the southwest and on the southern edge of Japan) were undertaken. Whereas resistivity distributions varied with the current frequency depending on the field, C_v distributions were consistent regardless of the frequency common to the three test fields. Although the resistivity characteristics did not indicate the existence of a groundwater table or aquifer, C_v for the frequency range of 21–40 Hz can be used to specify the locations of the table and aquifer and additionally the doline in the limestone aquifer field. An electrokinetically induced vibration of porous material was the most plausible mechanism that explains the large C_v in the specific frequency range. The effectiveness of using C_v and the developed variable-frequency-based electric sounding system were thus demonstrated by modeling and field experiments.

由于城市化，工业和农业的全球发展，对地下水资源的需求增加了。因此，需要可用于精确勘测地下水资源的先进地球物理技术。尽管电测深已成为测量的标准技术，但仅考虑电阻率和感应极化时，仍然难以准确指定地下水位和含水层分布。本文旨在通过开发一种基于频率的电测深系统来提高精度，该系统以1 Hz的间隔测量在1-100 Hz的电流传输频率范围内的视电阻率。使用土壤样品和基于储罐的含水层模型进行的实验表明，电阻率的变化系数（C_v）在21–40 Hz的频率范围内有效检测含水层，因为它高于其他频率范围内的系数。为了验证该指标的可用性，进行了三个不同地质背景的田间试验（即位于日本西南部和南部边缘的高原，沿海和石灰岩含水层田）。电阻率分布随磁场的变化而变化，而C _v分布却是一致的，而与三个测试场的频率无关。尽管电阻率特性未表明存在地下水位或含水层，但C _v频率范围为21–40 Hz的频率可以用来指定工作台和含水层的位置，以及石灰岩含水层字段中的轮廓线。多孔材料的电动感应振动是最合理的机制，可以解释特定频率范围内的大C _v。通过建模和现场实验证明了使用C _v和开发的基于变频的电测深系统的有效性。