• Title/Summary/Keyword: 굴절법 탄성파탐사

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공주 공산성 원형연못의 지반에 대한 탄성파 굴절법 탐사

  • 변성환;오진용;서만철
    • 한국지구물리탐사학회:학술대회논문집
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    • 2004.06a
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    • pp.132-138
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    • 2004
  • 탄성파 탐사는 인공지진파를 이용하여 지표면 하부의 물성을 알아내는 지구물리탐사로서 20 세기 초부터 석유탐사와 공학적 지반조사에 가장 널리 사용되었다. 굴절법 탄성파 탐사는 지층의 탄성파 속도를 알아내는 방법으로서 최근에는 석조문화재 등의 지반특성 조사에서 사용된 예가 있다. 이번 연구에서는 공주 공산성의 쌍수정 광장에 위치하는 공산성 원형연못 주변의 지반에 대하여 굴절법 탐사를 실시하였다. 쌍수정 광장은 기존의 발굴조사를 통하여 백제 추정왕궁지가 위치한 곳으로 알려졌으며, 광장 남쪽에 원형연못(상면직경 7.3 m, 바닥직경 4.78 m, 높이 3 m)도 발굴되었다. 원형연못 주변에 5개 탄성파 측선을 설치하였고, 해머 타격점과 수신기의 배열을 3가지 다른 방식을 적용하여 24 m, 31 m, 48 m 측선깊이의 굴절법 자료를 얻었다. 대체로 공산성 원형연못 주변의 지반은 3개 층으로 구성되어 있다. 각 층의 겉보기 속도는 약 261${\~}$391 m/s, 약 591${\~}$992 m/s, 약 1950${\~}$3230 m/s이며, 첫 번째와 두 번째 층의 두께는 각각 약 2${\~}$2.4 m 와 4.6${\~}$8.6 m이다. 일반적으로 최하부 층의 속도는 기반암, 상부층들의 속도는 풍화토에 대응한다. 그러나 두 번째 층의 주시곡선 형태와 속도범위는 국내 석탑 문화재 하부의 것과 유사한 것으로 보아 공산성 연못주변은 인공적인 기초지반의 가능성을 제기하며, 그렇다면 공산성 원형연못은 파내려 간 것보다는 쌓아 올렸을 것이다.

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On-Land Seismic Survey of Korea (한국의 육상 탄성파탐사)

  • Kwon, Byung-Doo
    • Economic and Environmental Geology
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    • v.39 no.4 s.179
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    • pp.441-450
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    • 2006
  • The on-land seismic survey in Korea was begun in mid-1960s. Kim et al.(1967) of Korea Geological Survey reported on the result of gravity and seismic reflection surveys conducted in the Pohang area for the period of 1963-64 to assess its possibility of oil entrapment. Hyun and Kim (1966) carried out a refraction survey on the tunnel wall. Since then, the KGS geophysicists had conducted seismic surveys on Kyungsang sedimentary basin as a main project for several years. In 1970s, on-land seismic surveys had been conducted for various purposes such as site investigation for the nuclear power plants and industrial complex, exploration for ground water, mineral resources and underground tunnel. The first reflection survey with CMP acquisition was attempted in 1978 by using a digital recording system. But most of on-land seismic surveys had employed the refraction method until 1980s. In 1990s, high resolution reflection and various borehole seismic surveys such as tomography, uphole, downhole, cross-hole methods have been attempted by universities and engineering companies. The applications of on-land seismic surveys have been enlarged for both academic and industrial purposes such as investigation of geologic structure of the fault and tidal flat area, construction of highway, railroad and dam, geothermal energy and mineral resource exploration, environmental assessment for waste disposal sites and archaeological investigations. In 2002, the first crustal seismic survey was carried out on the profile of 294km length across the whole peninsular. It is expected that the advanced technology and experience acquired through offshore seismic surveys, which have been conducted in continental shelf of Korea and foreign oil fields, will stimulate the more active on-land seismic explorations.

Seismic Refraction Analysis to Estimate the Depth to the Bedrock: Case Study (기반암 깊이 도출을 위한 굴절법 탄성파 자료 분석: 사례연구)

  • Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.8 no.4
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    • pp.237-242
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    • 2005
  • A seismic refraction study in estimation of depth to the bedrock demonstrates that 1) the average velocity in the medium is about 250 m/s in the surface layer (< 4 m), 2,500 m/s in the weathered formation, and greater than 3,000 m/s in the bedrock, 2) the depth to the deepest reflector assumed to be the bedrock is about 17 m; however, according to the cores collected in a borehole in study area, the bedrock (granite) occurred at depth 25 m, 3) according to the density and velocity logging, at depth 17 m, a measurable velocity and density increase are observed, and 4) the velocity of the weathered formation is relatively high and therefore, the acquisition offsets ($70{\sim}80m$) are turned out not to be long enough to record the refracted signal from the bedrock at depth 25 m as first arrivals.

연속 굴절파 중합 방식을 활용한 충적층 지하수위 조사기법 소개 및 현장 응용

  • 김형수;김중열;김유성
    • 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.

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지반 개량된 조간대 퇴적층에 대한 물리탐사 연구

  • 김성욱;이현재;김인수
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2002.09a
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    • pp.319-322
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    • 2002
  • 그라우팅으로 지반 개량된 조간대 퇴적층의 지층구조를 규명하기 위한 방법으로 전기비저항탐사, 굴절법 탄성파탐사, 지하레이더탐사를 실시하였다. 연구대상 지반의 10m 전후 심도에서 해수의 영향을 받는 수평의 저비저항대가 발달하며, 저비저항대는 모래가 우세한 지층에 해당한다. 지반의 탄성파 속도는 1~3km/sec의 범위로 조간대의 미고결 퇴적층과 비교할 때 매우 높은 속도에 보여준다. 지반의 높은 속도는 지반 개량의 효과로 판단된다. 지하레이더탐사에서 퇴적층의 구성 물질에 따라 교반 정도가 달지는데 모래층은 퇴적물과 주입제의 교반이 잘 이루어져 불규칙한 반사면으로 나타나며, 점토층은 교반이 불량하여 개량된 부분은 주상으로 관찰된다. 물리탐사의 결과와 시추조사를 대비할 때 지반 개량은 기반암까지 시행되었으며, 양호한 암반을 지시하는 고비저항대와 고속도층은 내륙으로 갈수록 깊은 심도를 보여준다. 이것은 지반 개량 이전의 기반암 심도와는 상반되는 것으로 지반 개량의 효과는 해안방면의 지층에서 잘 나타난다.

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Maximising the lateral resolution of near-surface seismic refraction methods (천부 탄성파 굴절법 자료의 수평 분해능 최대화 연구)

  • Palmer, Derecke
    • 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.

A Study on the Shallow Marine Site Survey using Seismic Reflection and Refraction Method (탄성파 반사법 및 굴절법을 이용한 천해저 지반조사에 대한 연구)

  • Shin, Sung-Ryul;Kim, Chan-Su;Jo, Churl-Hyun
    • Geophysics and Geophysical Exploration
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    • v.11 no.2
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    • pp.109-115
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    • 2008
  • It is very important to estimate the physical properties of survey area and delineate the geological basement in marine site survey for the design of offshore structures. For the purpose of providing high quality data by means of engineering site survey, it is necessary to apply several survey techniques and carry out the integrated interpretation to each other. In this study, we applied single channel seismic reflection method and OBC (Ocean Bottom Cable) type seismic refraction method at shallow marine. We used a dual boomer-single channel streamer as a source-receiver in seismic reflection survey and airgun source-the developed OBC type streamer in seismic refraction survey. We made 24 channels OBC type streamer which has 4m channel interval and each channel is composed of single hydrophone and preamplifier. We tested the field applicability of the proposed method and applied the typical seismic data processing methods to the obtained reflection data in order to enhance the data quality and image resolution. In order to estimate the geological velocity distribution from refraction data, seismic refraction tomography technique was applied. Therefore, we could successfully perform time-depth conversion using the velocity information as an integrated interpretation. The proposed method could provide reliable geologic information such as sediment layer thickness and 3D basement depth map.

Case study on the lake-land combined seismic survey for underground LPG storage construction (LPG 지하저장기지 건설을 위한 수륙혼합 탄성파탐사 사례)

  • Cha Seong-Soo;Park Keun-Pil;Lee Ho-Young;Lee Hee-Il;Kim Ho-Young
    • 한국지구물리탐사학회:학술대회논문집
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    • 2002.09a
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    • pp.101-125
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    • 2002
  • A lake seismic survey was carried out to investigate possible geohazards for construction of the underground LPG storage at Namyang Lake. The proposed survey site has a land-lake combined geography and furthermore water depth of the lake is shallow. Therefore, various seismic methods such as marine single channel high resolution seismic reflection survey, sonobuoy refraction survey, land refraction survey and land-lake combined refraction survey were applied. Total survey amounts are 34 line-km of high resolution lake seismic survey, 14 lines of sonobuoy refraction survey, 890 m of land refraction survey and 8 lines of land-lake combined refraction survey. During the reflection survey, there were severe water reverberations from the lake bottom obscured subsurface profiling. These strong multiple events appeared in most of the survey area except the northern and southern area near the embankment where seems to be accumulated mainly mud dominated depositions. The sonobuoy refraction profiles also showed the same Phenomena as those of reflection survey. Meanwhile the results of the land-lake combined refraction survey showed relatively better qualities. However, the land refraction survey did not so due to low velocity soil layer and electrical noise. Summarized results from the lake seismic survey are that acoustic basement with relatively flat pattern appeared 30m below water level and showed three types of bedrock such as fresh, moderately weathered and weathered type. According to the results of the combined refraction survey, a velocity distribution pattern of the lake bottom shows three types of seismic velocity zone such as >4.5 km/s, 4.5-4.0km/s and <4.0km/s. The major fault lineament in the area showed NW-SE trend which was different from the Landsat image interpretation. A drilling was confirmed estimated faults by seismic survey.

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Near-surface geophysical studies in the Ulsan Fault Zone of Korea (한국 울산단층대에서의 천부지구물리 연구)

  • Kim, Ki-Young;Kim, Dong-Hoon;Lee, So-Young
    • Geophysics and Geophysical Exploration
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    • v.11 no.1
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    • pp.78-84
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    • 2008
  • Recent earthquakes near nuclear power plants in Korea have triggered public concerns about possible seismicity of the Ulsan Fault Zone in the south-eastern part of the Korean peninsula. To reveal subsurface structures of this fault zone, we conducted high-resolution seismic refraction and reflection surveys, and closely spaced gravity measurements in the Dongchon River valley north of Ulsan, Korea. Here alluvium covers the north-south trending fault zone in a 1-km wide valley. Both source points and receivers were spaced at 5-m intervals for the 24-channel seismic refraction and reflection methods, along two profiles of 835 m and 415 m length. Gravity data were also measured along these profiles at 131 stations using a 10-m interval. Synergetic interpretation of seismic refraction, high-resolution seismic reflection, and gravity surveys across the valley indicates that the Ulsan Fault Zone was formed by apparent north-south strike-slip motions during the Cretaceous, and that some faults may have been reactivated by east-west compressional or transpressional stresses during the Tertiary or Quaternary.

Geophysical Explorations for Safety Analysis of Bangeosan-Maaebul(Stone Relief Bhaisajyaguru triad at Mt. Bangeosan) (방어산 마애여래입상의 안전진단을 위한 지구물리탐사)

  • O, Seon-Hwan;Seo, Man-Cheol
    • Journal of the Korean Geophysical Society
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    • v.4 no.1
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    • pp.11-20
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    • 2001
  • Seismic refraction and electrical resistivity surveys were conducted in Bangeosan Maaebul site located in Haman, Kyungnam, in order to present geophysical safety analysis method for masonry cultural properties. Seismic refraction exploration revealed that the ground was composed of three layers in term of seismic wave velocity; the upper, medium, and lower layers. The low velocity ranging from 308 to 366 m/sec in upper layer suggests weathered soil, the intermediate velocity from 1906 to 2090 m/sec in the medium layer indicates weathered rocks, and the high velocity from 5061 to 5650 m/sec in the lower layer implies extremely hard rocks. Our seismic result suggests that the upper and medium layer around the Maaebul should be reinforced to support the construct. The result of electric resistivity survey shows that there exists a low resistivity zone, ranging from 131 to 226 Ohm-m, at the right side of the Maaebul with the direction of NE-NNE. This area is the weakness zone as it plays role of the underground water passage in rainy season.

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