• Title/Summary/Keyword: 천부 탄성파탐사

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Surface Geophysical Survey for Delineation of Weathered Zone of Chojeong Area and Investigation of Fault Fracture Zones (초정지역의 풍화대 조사 및 단층파쇄 지역의 불연속면 조사를 위한 지표물리탐사)

  • Kim, Ji-Soo;Han, Soo-Hyung
    • The Journal of Engineering Geology
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    • v.17 no.4
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    • pp.517-523
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    • 2007
  • Geophysical surveys(seismic refraction, electrical resistivity, and ground penetrating radar) were performed to delineate the weathering zone associated with vadose water in Chojeong area and investigate the fault related fracture zones. On the basis of seismic velocity structures, weathering layer for the southwestern part is interpreted to be deeper than for the northeastern part. The depth to bedrock(i.e., thickness of weathered zone) from seismic refraction data attempted to be correlated with drill-core data and groundwater level. As for the investigation of geological discontinuities such as fault related fracture zone, seismic refraction, electrical resistivity, and ground penetrating data are compositely employed in terms of velocity and resistivity structures for mapping of surface boundary of the discontinuities up to shallow depth. Surface boundaries of fracture zone are well indicated in seismic velocity and electrical resistivity structures. Accurate estimation of weathered zone and fracture zone can be successfully available for mapping of attitude of vadose water layer.

Site Characteristics Around the Gongsansung Circular Pond in Gongju Based on the Seismic Methods (탄성파탐사를 이용한 공주 공산성 원형연못의 지반조사)

  • Oh, Jin-Yong;Suh, Man-Cheol
    • Economic and Environmental Geology
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    • v.38 no.6 s.175
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    • pp.623-631
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    • 2005
  • We applied the seismic method to investigate the site characteristics around the Circular Pond (top diameter 7.3 m, bottom diameter 3 m, and depth 4.78 m) at the Ssangsujung Park within the Gongsansung in Gongju. Previous excavations for the cultural assets beneath the Ssangsujung Park disclosed the assumed site of the Palace of the Beakje Dynasty and the Circular Pond containing the Bakje relics. We demonstrated that the seismic prospecting can be applicable to delineate the underground structure around the cultural properties by the three kinds of seismic approaches: walk-away test, conventional refraction method, and equal-distance refraction survey. The last method which is designed by this work ran detect the I-W variations of seismic velocity in the subsurface medium across the Circular Pond on the basis of the difference of the P-wave arrival times between the 1-m-spacing 24 geophones and the corresponding 24 shots parallel with the geophone profile. From the combined results, prominent three-layer velocity structure is observed around the Circular Pond. The bottom layer is interpreted as the basement rock which is exposed near the Ssangsujung whereas the upper layer with relatively lower velocities is interpreted to be the artificial covering. The basement depth beneath the Circular Pond is deeper than the norhern area. The western basement of Circular Pond has the thicker weaker layer compared with the eastern part. Thus, the middle layer could be constructed as the artificial foundation during the Beakje Dynasty. Consequently, the Kong-sansung Circular Pond is possibly built upwardly rather than digging.

Considerations on the Difficulties in Velocity Logging in the Near Surface Environments (천부 지반 환경에서 속도검층 난제들에 대한 고찰)

  • Jo, Churl-Hyun;Byun, Joong-Moo;Hwang, Se-Ho
    • Geophysics and Geophysical Exploration
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    • v.9 no.3
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    • pp.185-192
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    • 2006
  • Cares should be taken when performing the P and S wave velocity loggings in engineering and environmental fields. Some of them are the effect of casing, which is installed to prevent the borehole collapsing when the drilling is done on the loose ground such as soil and/or soft rock, and the discrepancy of the velocities of the same media according to the difference of the source wave frequency spectrum. The elastic moduli obtained from the P and S wave velocity logging have the dynamic characteristics. To overcome these difficulties, the following suggestions are recommended; (1) develop and apply a careful drilling technique that can keep the borehole wall without a casing, and (2) apply the logging methods with the suitable frequency bandwidth for the object of the velocity logging. It is important to make the aseismological engineers understand the difference between the dynamic elastic moduli and the static ones obtained from mechanical test, and to advise them to use the information properly.

Study on the Characteristics of Gas Hydrate Layers Distributed in the Southern Ulleung Basin, the East Sea (동해 울릉분지 남부해역에 분포하는 가스 하이드레이트층의 특성 연구)

  • Huh Sik;Yoo Hai-Soo;Kim Han-Joon;Han Sang-Joon;Lee Yong-Kuk
    • The Korean Journal of Petroleum Geology
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    • v.10 no.1_2 s.11
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    • pp.18-22
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    • 2004
  • To identify and interpret the distribution and the characteristics of the gas hydrate layers in the Ulleung Basin, we have surveyed and gathered the multi-channel seismic data, Chirp sub-bottom profiler, SeaBeam and 12 m piston core samples since 1996. In previous works, high-resolution seismic profiles showed acoustic anomalies such as acoustic void, acoustic turbidity and pock mark which indicate the presence of gas-charged sediments. The patterns of horizontal degassing cracks originated from free methane expansion is the strong indicator of shallow gas-charged sediments in the core samples. The observation of submarine slides and slumps from destabilizing the sediments in the southern part of the Ulleung Basin may also point out that the gas had been released from gas hydrate dissociation during lowstand of sea level. The multi-channel seismic data show BSR, blanking and phase reversal. The gas hydrate layers above which large-scale shallow gases are distributed exist at the depth of about 200 m from the sea-floor with water depth of 2,100 m. From the interpretation of seismic sections in the southern Ulleung Basin, gas hydrate layers occur in the Pleistocene-Holocene sediments. These gas-charged sediments, acoustic anomalies and BSR may be all related to the existence of gas hydrate layers in the study area.

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Directional Characteristics of Sleeve-gun Arrays in Marine Seismic Survey (해양 탄성파 탐사에서 슬리브건 배열의 방향 특성)

  • Yoo, Hai-Soo;Yang, Sung-Jin
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.1
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    • pp.71-80
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    • 1996
  • Characteristics of sleeve-gun arrays installed on the R/V Onnuri were analyzed and compared with survey data. In the case of cluster array, the beam width in the frequency range up to 814Hz is constant as $179.5^{\circ}$, and rapidly narrows in the frequency range of 814-1631Hz. However, in the case of long and wide arrays, as the frequency increases, the beamwidth decreases. The optimal frequency is 69Hz. the main lobe of vertical inclination has its maximum amplitude at phase angle $0^{\circ}$. The optimal frequency of cluster array which produces little side lobe is less than 1631Hz, and those of long and wide arrays are less than 108Hz. As a result, the cluster array produces a good source for high-resolution seismic survey, while the long and wide arrays are suitable for the survey of deep structures. The final high-resolution seismic section with cluster array was compared with that of long and wide arrays.

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Case studies of shallow marine investigations in Australia with advanced underwater seismic refraction (USR) (최신 수중 탄성파 굴절법(USR)을 이용한 호주의 천부해양탐사 사례연구)

  • Whiteley, Robert J.;Stewart, Simon B.
    • Geophysics and Geophysical Exploration
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    • v.11 no.1
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    • pp.34-40
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    • 2008
  • Underwater seismic refraction with advanced interpretation approaches makes important contributions to shallow marine exploration and geotechnical investigations in Australia's coastal areas. A series of case studies are presented to demonstrate the recent applications of continuous and static USR methods to river crossing and port infrastructure projects at various sites around Australia. In Sydney, static underwater seismic refraction (USR) with bottom-placed receivers and borehole seismic imaging assisted the development of improved geotechnical models that reduced construction risk for a tunnel crossing of the Lane Cove River. In Melbourne, combining conventional boomer reflection and continuous USR with near-bottom sources and receivers improved the definition of a buried, variably weathered basalt flow and assisted dredging assessment for navigation channel upgrades at Geelong Ports. Sand quality assessment with continuous USR and widely spaced borehole information assisted commercial decisions on available sand resources for the reclamation phase of development at the Port of Brisbane. Buried reefs and indurated layers occur in Australian coastal sediments with the characteristics of laterally limited, high velocity, cap layers within lower velocity materials. If these features are not recognised then significant error in depth determination to deeper refractors can occur. Application of advanced refraction inversion using wavefront eikonal tomography to continuous USR data obtained along the route of a proposed offshore pipeline near Fremantle allowed these layers and the underlying bedrock refractor to be accurately imaged. Static USR and the same interpretation approach was used to image the drowned granitic regolith beneath sediments and indurated layers in the northern area of Western Australia at a proposed new berthing site where deep piling was required. This allowed preferred piling sites to be identified, reducing overall pile lengths. USR can be expected to find increased application to shallow marine exploration and geotechnical investigations in Australia's coastal areas as economic growth continues and improved interpretation methods are developed.

A study of push core sediments and topographical controls around the shallow gas hydrate site in the Ulleung Basin, East Sea (울릉분지 천부 가스하이드레이트 부존지역에서의 해저지형변화에 따른 퇴적물 특성 연구)

  • Chun, Jong-Hwa;Lee, Joo-Yong;Kim, Hak-Joo;Kang, Nyeon-Keon;Nam, Sung-Il
    • 한국신재생에너지학회:학술대회논문집
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    • 2008.10a
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    • pp.200-202
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    • 2008
  • 동해 울릉분지에서는 시추선 RemEtive를 사용하여 UBGH-X-01 가스하이드레이트 탐사가 2007년에 실시되었다. 본 연구에서는 천부 가스하이드레이트가 확인된 UBGH1-10 정점에서 무인잠수정(Quantam WROV)을 사용하여 획득된 푸쉬코어와 해저지형 분석을 수행되었다.UBGH1-10 정점은 seismic chimneys의 탄성파 특성이 발달된 지역이다. 이곳에서는 해저표면으로부터 수 m 하부에서 가스하이드레이트가 발견되었다. 이 정점은 수 m 높이의 얕은 둔덕들이 무인잠수정에 부착된 비디오 카메라에 의해서 관찰되었다.이곳에서 채취된 길이 약40 cm의 푸쉬코어는 생물교란된 뻘질 퇴적물로 구성되어 있으며, 가스하이드레이트와 chemosynthetic community는 관찰되지 않았다. 푸쉬코어는 X-ray fluorescence scanner를 사용하여 퇴적물의 26가지 원소 조성을 분석하였다. UBGH1-10 정점의 산화환원환경은 Mo/Al과 Mn/Ti 원소비를 이용하여 천부 가스하이드레이트가 발견되지 않은 UBGH1-9와 UBGH1-1 정점과 대비하였다. 이 정점의 일차생산력은 Ba/Al 원소비를 이용하여 다른 정점과 대비하였다. 천부 가스하이드레이트가 발견된 UBGH1-10 정점은 활발한 가스방출과 관련된 생물집단 서식 또는 자생광물 형성의 흔적이 발견되지 않으며, 퇴적물에서도 산화환원환경과 일차생산력의 큰 차이가 관찰되지 않는다.

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Subsurface Imaging using Headwave Stacking (선두파 중합을 이용한 천부지층의 영상화)

  • Park Jung-Jae;Ko Seung-Won;Shin Chang-Soo;Suh Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.5 no.3
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    • pp.178-184
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    • 2002
  • For economy and convenience, seismic refraction survey is widely used in surveying for large civil engineering work. The purpose of this study is to obtain the numerical responses of various models using Kirchhoff migration, and to analyze its application to the real data processing. Synthetic traveltime curve was calculated by vidale's algorithm, and various models such as 2 or 3 layer model and irregular topography model are tested to simulate the response of real structure. In order to compare the effect of initial velocity model, true velocity models, inversion results by tomography, smooth velocity models are used as an initial guess. The responses of model data show that the algorithm of this study is more sensitive to initial velocity model than the reflection survey, so choosing a suitable initial velocity model will be the most important thing in real data processing.

Geophysical Surveys for the Detection of Gallery and Geomembrane at the Imcheon Abandoned Mine (임천 폐광산의 지하갱도와 인공차수막의 탐지를 위한 지구물리탐사)

  • 김지수;한수형;이경주;최상훈
    • Economic and Environmental Geology
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    • v.36 no.6
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    • pp.501-510
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    • 2003
  • Several geophysical surveys(electrical resistivity, electromagnetic, seismic refraction, CPR) were conducted to primarily investigate the gallery and the geomembrane at an abandoned mine(Imcheon mine). The subsurface structure mapped from seismic refraction survey mainly consists of three velocity layers(>1000 m/s, 1000∼2000 m/s,<2000 m/s). Top of the bedrock, whose velocities exceed 2000 m/s, appears to be at depth of 7.5∼10m. Higher resistivities (of ten thousands-hundred of thousands ohm-m) are interpreted to be associated with a open(cavities) gallery. The events at depth of approximately 0.5∼0.7m in GPR sections are probably caused by high-density-poly-ethylene geomembrane. Taking into consideration of the differences in the spatial resolution between georadar and electrical surveys, the events of geomembrane correspond to the top of the high resistivities at depth of about 2m. The segments, characterized with the higher conductivities in the electromagnetic data and the lower resistivities in the electrical resistivity data, are probably associated with surface water or tear zone of geomembrane.

Reverse-time Migration using Surface-related Multiples (자유면 기인 겹반사파를 이용한 거꿀시간 참반사 보정)

  • Lee, Ganghoon;Pyun, Sukjoon
    • Geophysics and Geophysical Exploration
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    • v.21 no.1
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    • pp.41-53
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    • 2018
  • In the traditional seismic processing, multiple reflections are treated as noise and therefore they are eliminated during data processing. Recently, however, many studies have begun to consider multiples as signals rather than noise for seismic imaging. Multiple reflections can illuminate an area where primary reflections are not able to cover, thus it is allowed that a smaller number of shots and receivers are used for imaging large areas. In order to verify this, surface-related multiples were used for reverse-time migration (RTM), and then we compared the results with conventional RTM images which are generated from primary reflections. To utilize multiples, we separated multiples from whole seismic data using surface-related multiple elimination (SRME) method. Numerical examples confirmed that the migration using multiples can image wider area than the conventional migration, particularly in the shallow subsurface layers. In addition, the migration of multiples could eliminate the acquisition footprints.