Changryol Kim

Application of electrical resistivity tomography (ERT) technique to detect underground cavities in a karst area of South Korea

Recently, the electrical resistivity tomography (ERT) technique has been increasingly applied to underground cavity detection filled with groundwater and/or clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in a karst area in Korea. Numerical ERT modeling and inversion were carried out to select appropriate field survey parameters. Two geological structures, similar to those that exist in the field survey area, were modeled: a sinkhole model and a vein-type structure. Electrode configurations using pole–pole, pole–dipole, dipole–pole, and dipole–dipole arrays were tested with the two geologic models and compared. The numerical modeling showed that the resistivity distribution of the ERT tomogram using the pole–dipole array produced the best representation of the two models. The pole–dipole and pole–pole array configurations were applied in an ERT field survey using six boreholes. The field ERT results show that cavity areas filled with clay or groundwater appeared as low-resistivity anomalies in the limestone formation. This was particularly evident in the inclined vein-type structures attributed to fracture zones, where the field data were similar to the modeling results. Therefore, the ERT technique could be effectively used for detecting underground limestone cavities under similar geological conditions as those at our study area.

Detection of cavities in a karst area by means of a 3D electrical resistivity technique

In this study, we examined the applicability of a 3D electrical resistivity technique for the probing of underground cavities at a field test site in a karst area in Yongweol-ri, Muan-gun, in the south-western part of the Korean peninsula. At the test site, where the ground has subsided in the past, underground cavities are commonly found in the limestone bedrock, which is overlain with alluvial deposits. The limestone cavities at the test site are mostly filled with groundwater and clay; hence, they show levels of electrical resistivity that are significantly lower than those of the surrounding host bedrock. The results of this study demonstrate that the zones of low resistivity correspond to the zones of the cavities identified in the boreholes at the site, and that our 3D electrical resistivity survey is a very effective tool for detecting and mapping underground cavities in a karst area.

The effect of the antenna height on quality of bistatic GPR data

In various ground-penetrating radar (GPR) systems, antennas can not be in contact with ground medium perfectly. In this paper, we analyzed the effect of the antenna elevation on quality of bistatic GPR data. For this study, a pair of resistively-loaded dipoles with broadside (BD) and endfire (EF) configurations was modeled. In the numerical model, a ground medium contains an infinite perfect electric conductor (PEC) plane as a target. Based on this model, peak-to-peak voltages of GPR signals depending on the height of the antenna for each configuration were observed. This study would help consider the proper range of the height of the antenna for sufficient quality of GPR signals.

Potential Mapping of Moisan area Using SIP and 3D Geological Modeling

요약: 광물자원탐사 기술 개발의 일환으로 광대역 유도분극 탐사 자료를 활용한 광체의 부존 가능성 평가를 위해 모이산 지역에 대한 3차원 포텐셜 지도 구축 연구가 수행되었다. 현장 탐사 결과를 지질모델링 영역별로 해석하여 광체 영역에서 나타나는 위상 및 전기비저항 값의 분포 특성을 해석하였으며, 이를 바탕으로 모이산 광체에 대한 부존 잠재성 평가를 수행하였다. 잠재성 평가 결과 기존에 확인된 광체 영역에서는 높은 부존 가능성이 확인되었으며, 최근 시추를 통해 확인된 일부 광체 영역에서도 주변부에 비해 잠재성이 높은 것으로 해석되어 신뢰도가 높음을 확인하였다. 광체 분포특성에 따라 효과적으로 측선 설계가 이루어지고 보다 조밀한 광대역 유도분극 탐사 자료를 얻을 경우 이번 연구를 통해 습득한 해석 기술은 광체 평가에 효율적으로 적용될 수 있을 것으로 판단된다. 주요어: 3차원 지질모델링, 포텐셜 지도, 모이산Abstract: In order to develop a new mineral exploration technique, a study was carried out about the potential mappingof Moisan area using SIP (Spectral Induced Polarization) data. The SIP inversion results were classified according tothe geological regions, and the distribution characteristics of resistivity and phase values of SIP data were analyzed atthe ore region. Based on the characteristics of SIP of ore bodies, we performed 3D potential mapping of Moisan area.The analyzed potential map was verified using that the locations and patterns of high potential regions of the resultsare well matched with those of the known ore bodies. If we get the higher spatial resolution SIP data, the potentialmapping technique using SIP data can be effectively applied to the estimation of mining deposit.Keywords: 3D geological modeling, potential mapping, Moisan