• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.78-83
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• 2002

The finite element method combined with the sensitivity method is adopted for 2-dimensionl Fourier transform inversion. To improve the efficiency of inversion calculation, multi-resolution wavelet method is proposed., Theoretical data which is obtained from above method is shown to examine the proposed method. Theoretical model assumes that underground cavity is located in limestone area. In theoretical model, 16 current and potential electrodes are located to get theoretical data. It is shown that the about inversion method is very exact and useful calculation method, in case the larger model is very small such as under ground cavity.

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.89-95
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• 2001

The final goal of the seismic method is to verify the spatial characteristic of subsurface media. For this purpose, professional interpreters interprete the discontinuities of seismic events from seismic image. This paper introduces a method for automatic discontinuity extraction from 3D seismic image. The method consists of three steps. The first step is for estimating coherency of seismic events from seismic data. The second step is to express the potential region where discontinuities may exist in the form of binary image. The third step is to locate the discontinuities by thining the region found in the second step.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.83-87
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• 2004

본 연구는 고해상도의 충적층 지하수위 분포 조사를 위한 탄성파 굴절법 조사 방법을 소개하고 부여 군수리 충적층 일대에서 이 기법을 통해, 획득된 실제 충적층내의 지하수위 조사 결과를 제시한다. 기본적으로 본 연구에서 활용된 연속 굴절파 중합 방식은 동일 공심점(common mid point, 이후 CMP)을 갖는 굴절파 신호를 취합하고, 이격 거리(offset)에 대한 시간 지연 효과 보정을 수행한 후, 이들 신호를 중합하여, 충적층의 지하수위면에서 굴절된 신호를 보다 뚜렷이 부각시켜 정확한 지하수위 정보를 획득 하는 방식으로 일명 CMP 굴절법이라고도 한다. 이 방식은 독일에서 최초 개발되었으나(Gebrande, 1986; Orlowsky 등, 1998), 국내에서 적용되기는 본 연구가 최초이다. 이러한 탄성파의 굴절 신호를 사용하는 방식은 우선, 기존의 일반적인 고해상도 반사법 탐사에서 잡음으로 여겨졌던 굴절파 신호를 활용할 수 있으며, 고해상도 반사법 탐사와 동일한 배열과 운영 방식으로 획득된 자료에서 원하는 정보를 획득할 수 있으므로, 고해상도 반사법에 의한 기반암 조사와 함께 적용될 경우, 정화한 충적 대수층의 분포를 조사할 수 있게 하여주는 획기적인 조사 신기술이다. 개발된 기법은 부여 군수리 충적층 지역을 대상으로 적용되었으며, 그 결과 기존의 어떠한 지구물리 조사 방법보다 정확하고 분명한 지하수위 분포를 보여주었다.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.285-292
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• 2007

Magnetotelluric data recorded in the middle part of the Korean Peninsula are contaminated by severe noises at dead-band frequencies. In this study, we estimated the location of noise source using a source localization method. Since conventional beamforming techniques were not adequate for the localization of electromagnetic sources, we used the matched field processing and a genetic algorithm. The solutions for the strong noise signals tend to be localized in a narrow area, whereas those for natural MT signals shows randomly distributed patterns. The strong noise sources are mainly located in the western part of Kyonggi-do.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.1-7
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• 2009

Airborne electromagnetics (AEM) is a useful tool for investigating volcanic structures because it can survey large and inaccessible areas. Disadvantages include lower accuracy and limited depth of investigation. The Grounded Electrical Source Airborne Transient Electromagnetic(GREATEM)survey system was developed to increase the depth of investigation possible using AEM. The method was tested in a survey at Mount Bandai in north-eastern Japan. Mount Bandai is an andesitic stratovolcano that rises 1819m above sea level. An eruption in July 1888 left a hoof-shaped collapsed wall in its northern crater and avalanche debris at its base. Previous surveys of Mount Bandai allow for comparisons of data on its structure and collapse mechanism as obtained by GREATEM and other geophysical methods. The results show resistive structures in recent volcanic cones and conductive structures in the collapsed-crater area. Conductive areas around the collapsed wall correspond to an alteration zone resulting from hydrothermal activity, supporting the contention that a major cause of the collapse associated with the 1888 eruption was hydrothermal alteration that structurally weakened the interior of the volcanic edifice.

• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.132-148
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• 2019

Recently, safety and environmental concerns have become major social issues. Especially, a special underground-safety law has been made and enacted to prevent ground subsidence around construction sites. For environmental problems, several researches have started or will start on characterization of contaminated sites, in-situ environmental remediation in subsurface, and monitoring of remediation results. As a part of the researches, geophysical surveys, which have been mainly applied to explore mineral resources, geological features or ground, are used to characterize not only contaminated areas but also fluid flow paths in subsurface environments. As a basic study for the application of geophysical surveys to detect contamination in subsurface, this paper analyzes previous researches to understand changes in geophysical properties of contaminated zones by various contaminants such as leachate, heavy metals, and non-adequate phase liquid (NAPL). Furthermore, this paper briefly introduces how geophysical surveys like direct-current electrical resistivity, induced polarization and ground penetration radar surveys can be applied to detect each contamination, before analyzing case studies of the applications in contaminated areas by NAPL, leachate, heavy metal or nitrogen oxides.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.177-183
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• 2008

The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.

• 한국지구물리탐사학회:학술대회논문집
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• 2002.09a
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• pp.85-100
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• 2002

This paper deals with a development of combined seismic methods, based on the application of Televiewer and seismic tomography, for the quantitative assessment of reclaimed body or dam at seashores in our county. The underground structure of reclaimed dam is very complex, mainly due to the unexpected exchange of rock fragments with the marine silty mud in conjunction with S.C.P. (Sand Compaction Pile) foundation, so that for several reasons only the use of Televiewer and seismic tomography for general application might not lead to a desirable resolution. Kinds of upgraded measuring and evaluation techniques for that are needed. For examples, a novel strategy for capturing the returning impulses from the outer side of casing plastic pipe is desired to be developed. For the tomograhy, one should be being more focussed on the study of raw data based on the wave propagation theory. In this paper, it is shown that such multidisciplinary approaches can be, by attempting to compare and jointly interpret the results from two methods, much efficient for understanding the reclaimed dam structure.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.237-240
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• 2007

The evaluation of shear modulus (or shear wave velocity) profile of site is very important in the various fields of geotechnical engineering. To obtain shear wave velocity profile, various in-situ seismic methods using surface waves have been developed. These surface wave based in-situ seismic methods have their own strength and weakness. In this study, new seismic site characterization method using the harmonic wavelet analysis of wave (HWAW) was proposed to overcome some of weaknesses in the existing surface wave based seismic site characterization methods. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. In order to estimate the applicability of HWAW method, field tests were performed. Through field applications and comparison with other test results, the applicability of the proposed method were verified.

• Journal of the Korean earth science society
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• v.31 no.7
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• pp.681-690
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• 2010

Inversion result of geophysical data given as a block type was geostatistically simulated with borehole observation given as a point type and was applied to the rock classifying map. The geophysical data generally involved secondary information for the target material and were obtained for overall region. In contrast, borehole data provided direct information for the target material, but tended to be effective only for a narrow range of region and were dealt as a point type. Integrated simulation or kriging interpolation of these two different kinds of information required the covariance for point-point, point-block and block-block. Using the Bssim module included in SGeMS software, integrated result of geophysical data and borehole data were obtained. The results were then compared with the method of geostatistical inversion proposed by authors. Downscaling method used in this study showed relatively more flexible than the geostatistical inversion.