• Geophysics and Geophysical Exploration
• /
• v.12 no.3
• /
• pp.268-277
• /
• 2009

Recently as the interest in the development of domestic ore deposits has increased, we can easily find some studies on exploration geophysics-based ore deposit survey in literature. Geophysical surveys have been applied to the investigation of both metallic and non-metallic ore deposit. For metallic ore-deposit survey, the 2D electrical resistivity method has been popularly used, because metallic mineral deposits are generally more conductive than surrounding media. However, geological structures are 3D rather than 2D structures, which may lead to misinterpretation in 2D inversion section. In this study, 3D effects are examined for several 3D structures such as a width-varying dyke model and a wedge-shaped model. We also investigate the effects of the direction of survey line. Numerical results show that the width-varying dyke model yields some low resistivity zone in the deep part, which is independent of real ore-body location. For the wedge-shaped model, even though the survey line is located apart from the ore body, the 2D inversion section still shows low resistivity zone in the deep part. When the survey line is not perpendicular to the strike of the ore body, the low resistivity zone is slightly broader but shallower than that obtained along the survey line perpendicular to the strike. For the survey lines that have an angle smaller than $45^{\circ}$ with the strike of the ore body, the inversion results are totally distorted. From these results, we conclude that 2-D survey and interpretation can lead to misinterpretation of subsurface structures, which may be linked to economical loss. Eventually, we recommend to apply 3-D rather than 2-D electrical resistivity survey for ore-deposit survey.

• Geophysics and Geophysical Exploration
• /
• v.7 no.2
• /
• pp.121-129
• /
• 2004

The geostatistical approach was applied to integrate MT (Magneto-telluric) resistivity data and borehole information for the spatial RMR (Rock Mass Rating) evaluation. Generally, resistivity of the subsurface is believed to be positively related to the RMR, thus the resistivity and borehole RMR information was combined in a geostatistical approach. To relate the two different sets of data, we take the MT resistivity data as secondary information and estimate the RMR mean values at unsampled points by identification of the resistivity to the borehole data. Two types of approach are performed for the estimation of RMR mean values. Then the residuals of the RMR values around the borehole sites are geostatistically modeled to infer the spatial structure of difference between real RMR values and estimated mean values. Finally, this geostatistical estimation is added to the previous means. The result applied to a real situation shows prominent improvements to reflect the subsurface structure and spatial resolution of RMR information.

• The Journal of Engineering Geology
• /
• v.9 no.1
• /
• pp.45-57
• /
• 1999

Groundwater flow in rock mass is controlled by the fractures developed in the area. So, the conductive fractures are very important for groundwater flow in crystalline rock. This study aims to find out the characteristics of the fracture distributed in granitic rock in the northern part of the Yusong area (latitude $36^{\circ}24'18"~36^{\circ}25'08",{\;}longitude{\;}127^{\circ}21'00"~127^{\circ}23'23"$). The electric and EM surveys were carried out in the site to delineate the fracture the fracture zones. Since geophysical survey provides non-unique solution, hydraulic data and dilling log data including BHTV scanning were used as complementary data to achieve the objective of this study. Electric survey(DC) arrays used are schlumberger and dipole-dipole arrays. VLF is used for EM survey. The main charcteristics of the fracture developed in the study aera are that fractures associated with basic dyke cut corss the main fracture zone in NNW and play an important role as hydraulic barrier. In trun, groundwater table in the upstream area is lower than that downstream area.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2002.09a
• /
• pp.134-139
• /
• 2002

살내 유적지의 발굴조사에서 지질물리학에 기초한 연구방법과 적용성을 검토하고자 발굴과 아울러 지구물리탐사를 실시하였다. 심도에 따라 구분한 전기비저항에서 토양 구성물질의 차이에 의한 전기비저항의 변화와 퇴적물의 공급방향을 유추할 수 있다. 지하레이더탐사의 반사단면에서 퇴적층의 분급과 입도에 따라 구분되는 층리의 경계를 규명할 수 있는데, 실트의 구성비가 높은 지층들의 반사면은 측방 연장성이 좋은 반면 자갈의 구성비가 높은 지층의 반사면들은 불규칙한 기복을 보여준다. 지층 반사면의 형태로부터 고환경의 정보를 획득할 수 있는데, 살래유적지의 경우 문화층은 세립의 실트와 모래와 우세한 지층에 해당하며 층서에서 자갈층의 반복과 지층 경사는 퇴적물의 공급에 관련되는 고수계의 위치와 하천의 지속적으로 범람하는 환경을 지시한다. 주거 유적지의 대자율탐사에서 유적지 경계부의 토양은 주변에 비해 낮은 대자율을 가진다. 대자율 이상대를 형성하는 토양은 주거지 내부에 한정되며 이들은 황색계열의 토색으로 소성에 의한 것으로 추정된다.

• Journal of the Korean Society of Groundwater Environment
• /
• v.1 no.1
• /
• pp.51-58
• /
• 1994

Electrical soundings and mappings were conducted to elucidate the geoelectrical structures of the local area of Cheju Island. The areas of the electrical surveys are coastal areas of Cheju Island, Gwagji, Sinpung-Sincheon. Generally, the geoelectrical structures of these areas are closely related with hydrogeological structures and it is very important to elucidate the geoelectrical structures for the water supply problems. Even though the results of electrical surveys in coastal areas of Cheju Island differ from place to place, there exists a general tendency of resistivity decrease with depth and the zone in the vicinity of mean sea level has low resistivity value. Also, there is good correlation between the low resistivity zone and the ground water distribution in the survey areas. A careful examination of the results of this study enabled resistivities of the rocks in Cheju Island to be divided in some categories. The resistivities of rocks unsaturated with ground water are greater than about 1000 ohm-m. The rocks saturated with fresh water have the resistivity value of about few hundreds ohm-m. Last, the rocks saturated with saline and/or brackish water have the resistivity value of about few tens ohm-m. The subsurface resistivity distribution of Cheju Island seems to be strongly dependent on the hydraulic characteristics of the rocks, and the amount and the salinity of the ground water in the rocks rather than the surface geology of the area.

• The Science & Technology
• /
• v.9 no.8 s.87
• /
• pp.23-27
• /
• 1976

우리나라에서 본격적으로 물리탐사를 시도한것은 1958~1960년에 실시한 항공자력탐사로서 그후 현재까지 불과 20년이 지나지 않았다. 그간 물리탐사의 기술발전으로 자원탐사분야에 많은 공헌이 있었다. 현재까지 주로 적용된 분야는 철자원탐사를 위한 자력탐사, 지하수조사를 위한 전기비저항탐사동, 연등의 통화금속광물탐사를 위한 각종 전기탐사, 제3기층 지질구조와 땜공사, 공업단지조성등의 기반암조사, 그리고 광산의 갱내 출수조사등을 위한 탄성파탐사, 우라늄자원을 위한 방사능탐사, 그리고 해저지질 및 자원조사를 위한 해상물리탐사등이다. 이와 동시에 석탄층조사를 위한 전기탐사 및 Model연구자력탐사의 전산처리 적용, 그리고 광물 및 암석의 물리적 성질등 학술분야에 대한 기초연구도 계속하여 왔다. 우리나라에 있어 물리탐사의 적용조건은 비교적 험악한 지형, 복잡한 지질구조, 광상의 불규칙 또는 소규모의 발달과 산재등이다. 이와 같은 특징은 탐사해석의 정도를 높이기 위하여 보다 고도의 과학기술문제의 해결을 요구하고 있으며 이와 동시에 현대적 탐사방법과 연구개발로 대상자원의 탐사지역확대와 지하심부 탐사등이 당면과제이다. 기술과제로서는 석탄 및 기타자원에 대한 물리검층탐사, 경상계 지질구조구명을 위한 탄성파탐사 및 동력탐사의 적용, 항공자력, 전자 및 방사능탐사 및 해양의 각종물리탐사의 기술개발이 있으며 그외 탐사자료의 전산처리기술 및 지구과학의 기초연구등이 있다.

• Geophysics and Geophysical Exploration
• /
• v.15 no.1
• /
• pp.33-38
• /
• 2012

A resistivity method has been applied to wide range of engineering and environmental problems with the help of automatic and precise data acquisition. Thus, more accurate modeling and inversion of time-lapse monitoring data are required since resistivity monitoring has been introduced to quantitatively find out subsurface changes With respect to time. Here, we used the finite element method (FEM) for 3D resistivity modeling since the method is easy to realize complex topography and arbitrary shaped anomalous bodies. In the FEM, the linear elements, also referred to as first order elements, have certain advantages of simple formulation and narrow bandwidth of system equation. However, the linear elements show the poor accuracy and slow convergence of the solution with respect to the number of elements or nodes. To achieve the higher accuracy of finite element solution, high order elements are generally used. In this study, we developed a 3D resistivity modeling program using high order Serendipity elements. Comparing the Serendipity element solutions for a cube model with the linear element solutions, we assured that the Serendipity element solutions are more accurate than the linear element solutions in the 3D resistivity modeling.

• Geophysics and Geophysical Exploration
• /
• v.10 no.4
• /
• pp.293-298
• /
• 2007

A new way to integrate various geophysical information for evaluation of RQD was developed. In this study, we does not directly define the RQD value where borehole data are not sampled. Instead, we infer the probability of RQD values with prior probability of data directly obtained from borehole, and secondary supporting probability from resistivity and seismic tomography data. First, we applied the geostatstical indicator kriging to get prior probability of RQD value, and indicator kriging with soft data to get the supporting probability from resistivity and seismic data. And we finally applied the permanence ratio rule to integrate these information. The finally obtained result was also analyzed to fully utilize the probabilistic features. For example, we showed the probability of wrongly classifying the RQD evaluation and vice versa. This kind of analytical result may be used for decision making process based on the geophysical exploration.

• Journal of the Korean GEO-environmental Society
• /
• v.14 no.4
• /
• pp.5-13
• /
• 2013

The water leakage of reservoir embankment usually occurs around channelling pipes, which gives little influence on the embankment in a normal state. However, the embankment can be destroyed when the water level of reservoir increases with heavy rain and the rainy season in summer. Investigating the water vein and its path is therefore very important from the viewpoint of disaster prevention and embankment maintenance. The water leakage in dams and levees where the channelling pipes are working as weak zone was analyzed by using both numerical simulation and experimental method in this study. To detect the water leakage, an electrical resistivity survey was used and investigated for its' usability. The numerical results show the size and location of weak zone increases the importance of selection of electrode spacing. The leakage experiments of model embankment present the best result is obtained under the conditions of electrode spacing of 0.3m and dipole-dipole array. By studying the water leakage in dams and levees, the electrical resistivity survey is observed it is a very useful method to predict the leakage.

• Geophysics and Geophysical Exploration
• /
• v.11 no.4
• /
• pp.326-334
• /
• 2008

The resistivity method has been used to image the electrical properties of the subsurface. Especially, this method has become suitable for monitoring since data could be rapidly and automatically acquired. In this study, we developed a time-lapse inversion algorithm for the interpretation of resistivity monitoring data. The developed inversion algorithm imposes a big penalty on the model parameter with small change, while a minimal penalty on the model parameter with large change compared to the reference model. Through the numerical experiments, we can ensure that the time-lapse inversion result shows more accurate and focused image where model parameters have changed. Also, applying the timelapse inversion method to the leakage detection of an embankment dam, we can confirm that there are three major leakage zones, but they have not changed over time.