• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.247-258
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• 2004

Two 3-dimensional data processing techniques to predict the fractured zone ahead of a tunnel face by the tunnel seismic survey were proposed so that the geometric formation of the fractured zone could be estimated. The first 3-dimensional data processing technique was developed based on the principle of ellipsoid, The input data needed for the 3D migration can be obtained from the 2-dimensional tunnel seismic prediction (TSP) test where the TSP test should be performed in each sidewall of a tunnel. The second 3-dimensional migration technique that was developed based on the concept of wave travel plane was proposed. This technique can be applied when the TSP is operated with sources in one sidewall of a tunnel while the receivers are installed in both sidewalls. New migration technique was applied to an in-situ tunnelling site. The 3-dimensional migration was performed using measured TSP data and its results were compared with the geological investigation results that were monitored during tunnel construction. This comparison revealed that the proposed migration technique could reconstruct the discontinuity planes reasonably well.

• Economic and Environmental Geology
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• v.47 no.6
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• pp.673-681
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• 2014

Recently, many countries in the world try to develop alternative energy sources, however, traditional hydrocarbon resources are still occupying most of the energy resources. Exploration demands for high technologies are increasing in the development of limited oil & gas resources field owing to the exhaustion of hydrocarbon resources for access area. Therefore, an effort for the development and the application of new technologies such as azimuth seismic survey, ocean-bottom seismic survey and marine controlled-source electromagnetic survey is necessary as well as an understanding of the existing technologies such as 2D/3D seismic survey. This dissertation is designed with the purpose of introducing marine hydrocarbon exploration technologies and analyzing their internalexternal researches, development and science information. In this study, we analised total 616 dissertations for the marine petroleum exploration released in the Sci-expanded DB of 'web of science' during the 2001~2014 periods.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.173-182
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• 2009

In April 2008, KIGAM carried out an ocean-bottom seismometer (OBS) survey in the central Ulleung Basin where strong bottom simulating reflectors (BSRs) were revealed from previous surveys and some gas-hydrate samples were retrieved by direct sampling. The purpose of this survey is to estimate the velocity structure near the BSR in the gas hydrate prospect area using wide-angle seismic data recorded on the ocean-bottom seismometers. Along with the OBS survey, a 2-D seismic survey was performed whereby stratigraphic and preliminary velocity information was obtained. Two methods were applied to wide-angle data for estimating P wave velocity; one is velocity analysis in the $\tau$-p domain and the other is seismic traveltime inversion. A 1-D interval velocity profile was obtained by the first method, which was refined to layered velocity structure by the latter method. A layer stripping method was adopted for modeling and inversion. All velocity profiles at each OBS site clearly show velocity reversal at BSR depths due to the presence of gas hydrates. In addition, we could confirm high velocity in the column/chimney structure.

• Geophysics and Geophysical Exploration
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• v.13 no.2
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• pp.159-168
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• 2010

Recent trend in petroleum/gas exploration is an application of 3D seismic exploration technique. Unlike the conventional 2D seismic data processing, 3D seismic data processing is considered as the one which requires expensive commercial software systems and high performance computer. This paper propose a practical 3D seismic processing methodology on a personal computer using public domain software such as SU, SEPlib, and SEPlib3D. The applicability of the proposed method has been demonstrated by successful application to a well known realistic 3D synthetic data, SEG/EAGE 3D salt model data.

• Geophysics and Geophysical Exploration
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• v.2 no.2
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• pp.77-85
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• 1999

The 3-D seismic research vessel, Tamhae II, was built to raise up the probability of the hydrocarbon discovery in the Korean continental shelf and the first test survey was completed in the East Sea. During the survey, the 240 channel 2-D marine seismic data were acquired by the Korean flag vessel for the first time. Tamhae II has been equipped with source, receiver, recording equipment, and navigation equipment as well as an onboard processing system. The source is composed of four subarrays and each subarray has six airguns. Total airgun volume is 4578 $in^3$. The receiver consists of two sets of 3 km long 240 channel streamer. In the first survey, the successful acquisition of 2-D seismic data was accomplished. From the result of the data processing, we confirmed that the high quality seismic data were acquired. For the high quality data acquisition, technology of survey design and planning, operation of vessel and equipments and systematic quality control should be developed.

• Geophysics and Geophysical Exploration
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• v.7 no.4
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• pp.245-250
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• 2004

Horizontal-axes on the seismic section have been represented in a distance unit by applying horizontal-distance correction transformation on a 2-D seismic section of single channel marine seismic data. By drawing horizontal-axes in a distance unit, distortion of horizontal distances shown on the seismic section when the ship speed varies during a survey can be diminished considerably. Position information obtained by GPS and stored in each trace of seismic data as well as data collection windows were used for horizontal distance correction. The minimum window length was decided by considering ship speed and shot interval, and the maximum window length wat determined by reflecting radius of the 1st Fresnel zone. In choosing an optimum window length, horizontal resolution and stacking effect were considered simultaneously. By applying horizontal distance correction we could get a 2-D seismic section which is considered at reflecting the real subsurface structure analogously.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.85-98
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• 2009

The tau-p inversion algorithm is widely employed to generate starting models with most computer programs, which implement refraction tomography. This algorithm emphasises the vertical resolution of many layers, and as a result, it frequently fails to detect even large lateral variations in seismic velocities, such as the decreases which are indicative of shear zones. This study demonstrates the failure of the tau-p inversion algorithm to detect or define a major shear zone which is 50m or 10 stations wide. Furthermore, the majority of refraction tomography programs parameterise the seismic velocities within each layer with vertical velocity gradients. By contrast, the Generalized Reciprocal Method (GRM) inversion algorithms emphasise the lateral resolution of individual layers. This study demonstrates the successful detection and definition of the 50m wide shear zone with the GRM inversion algorithms. The existence of the shear zone is confirmed by a 2D analysis of the head wave amplitudes and by numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, an analysis of the shot record amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients, occurs in the weathered layers. The major conclusion reached in this study is that while all seismic refraction operations should aim to provide as accurate depth estimates as is practical, those which emphasise the lateral resolution of individual layers generate more useful results for geotechnical and environmental applications. The advantages of the improved lateral resolution are obtained with 2D traverses in which the structural features can be recognised from the magnitudes of the variations in the seismic velocities. Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features such as faults which do not display any intrinsic variation or 'signature' in seismic velocities.

• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.71-77
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• 2002

We developed a modeling and visualization software that can analyze 3-dimensional seismic data. The software divides 3 dimensional space into a series of vertical and horizontal polygons, and allows the various seismic attributes and other spatial information to be stored on these polygons. The program can pick a particular pattern in semi-automatic mode, and store the pattern in the spatial DB. The pattern can be modeled and visualized in 3 dimensional space.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.88-93
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• 2004

본 논문에서는 현장에서 획득한 2차원 탄성파 탐사 자료를 처리하는 시스템을 제안한다. 일반적으로 탐사 자료는 매우 방대하여 효율적인 자료 처리 및 관리 시스템은 필수적이라고 할 수 있다. 본 논문에서는 모듈의 처리 과정에서 QC(Quality of Control)를 쉽게 하기 위해 윈도우 기반 GUI 환경을 제공할 뿐만 아니라, 모듈의 처리 흐름과 파라미터를 저장할 수 있는 템플릿 개념을 소개한다. 또한 객체 지향 개념을 도입하여 모듈들의 삽입, 삭제가 용이한 장점을 가지고 있다. 개발 환경은 MFC를 바탕으로 Windows 운영체제에서 개발되었다. 본 논문에서 개발된 시스템은 탄성파를 이용한 지반 조사에 효율적으로 사용될 수 있다고 사료된다.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.203-213
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• 2022

To understand an underlying geological structure via seismic imaging, the velocity information of the subsurface medium is crucial. Although the full-waveform inversion (FWI) method is considered useful for estimating subsurface velocity models, 3D FWI needs a lot-of computing power and time. Herein, we compare the calculation efficiency and accuracy of frequency-domain 2D and 3D acoustic FWIs. Thereafter, we demonstrate that the artifacts from 2D approximation can be partially suppressed via frequency-domain 2D FWI by employing diffraction angle filtering (DAF). By applying DAF, which employs only big reflection angle components, the impact of noise and out-of-plane reflections can be reduced. Additionally, it is anticipated that the DAF can create long-wavelength velocity structures for 3D FWI and migration.