• Title/Summary/Keyword: 탄성파 반사법

Search Result 113, Processing Time 0.026 seconds

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
    • /
    • v.5 no.3
    • /
    • pp.178-184
    • /
    • 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.

Interactive analysis tools for the wide-angle seismic data for crustal structure study (Technical Report) (지각 구조 연구에서 광각 탄성파 자료를 위한 대화식 분석 방법들)

  • Fujie, Gou;Kasahara, Junzo;Murase, Kei;Mochizuki, Kimihiro;Kaneda, Yoshiyuki
    • Geophysics and Geophysical Exploration
    • /
    • v.11 no.1
    • /
    • pp.26-33
    • /
    • 2008
  • The analysis of wide-angle seismic reflection and refraction data plays an important role in lithospheric-scale crustal structure study. However, it is extremely difficult to develop an appropriate velocity structure model directly from the observed data, and we have to improve the structure model step by step, because the crustal structure analysis is an intrinsically non-linear problem. There are several subjective processes in wide-angle crustal structure modelling, such as phase identification and trial-and-error forward modelling. Because these subjective processes in wide-angle data analysis reduce the uniqueness and credibility of the resultant models, it is important to reduce subjectivity in the analysis procedure. From this point of view, we describe two software tools, PASTEUP and MODELING, to be used for developing crustal structure models. PASTEUP is an interactive application that facilitates the plotting of record sections, analysis of wide-angle seismic data, and picking of phases. PASTEUP is equipped with various filters and analysis functions to enhance signal-to-noise ratio and to help phase identification. MODELING is an interactive application for editing velocity models, and ray-tracing. Synthetic traveltimes computed by the MODELING application can be directly compared with the observed waveforms in the PASTEUP application. This reduces subjectivity in crustal structure modelling because traveltime picking, which is one of the most subjective process in the crustal structure analysis, is not required. MODELING can convert an editable layered structure model into two-way traveltimes which can be compared with time-sections of Multi Channel Seismic (MCS) reflection data. Direct comparison between the structure model of wide-angle data with the reflection data will give the model more credibility. In addition, both PASTEUP and MODELING are efficient tools for handling a large dataset. These software tools help us develop more plausible lithospheric-scale structure models using wide-angle seismic data.

Seafloor Topographic Survey with Bedrock (기반암 정보를 포함한 해저 지형 조사 연구)

  • Kim, Myoung-Bae;Kwak, Kang-Yul
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
    • /
    • v.29 no.4
    • /
    • pp.343-349
    • /
    • 2011
  • Seabed topography and marine site survey should be performed first in the design and construction of marine structures. We could successfully acquire the seafloor topography information can be obtained by bathymetric survey and side scan sonar and the sediment layer thickness and 3D bedrock depth by seismic reflection. It is necessary to apply carry out the integrated interpretation to each other in the ocean civil Eng. In this paper, we have obtained information on the sea bottom topography and water depth at the same time using interferometer technique and on the basement depth by seismic reflection. We have performed to assess the proposed method on the seafloor topographic survey with bedrock.

S-wave Velocity Derivation Near the BSR Depth of the Gas-hydrate Prospect Area Using Marine Multi-component Seismic Data (해양 다성분 탄성파 자료를 이용한 가스하이드레이트 유망지역의 BSR 상하부 S파 속도 도출)

  • Kim, Byoung-Yeop;Byun, Joong-Moo
    • Economic and Environmental Geology
    • /
    • v.44 no.3
    • /
    • pp.229-238
    • /
    • 2011
  • S-wave, which provides lithology and pore fluid information, plays a key role in estimating gas-hydrate saturation. In general, P- and S-wave velocities increase in the presence of gas-hydrate and the P-wave velocity decreases in the presence of free gas under the gas-hydrate layer. Whereas there are very small changes, even slightly increases, in the S-wave velocity in the free gas layer because S-wave is not affected by the pore fluid when propagating in the free gas layer. To verify those velocity properties of the BSR (bottom-simulating reflector) depth in the gas-hydrate prospect area in the Ulleung Basin, P- and S-wave velocity profiles were derived from multi-component ocean-bottom seismic data which were acquired by Korea Institute of Geoscience and Mineral Resources (KIGAM) in May 2009. OBS (ocean-bottom seismometer) hydrophone component data were modeled and inverted first through the traveltime inversion method to derive P-wave velocity and depth model of survey area. 2-D multichannel stacked data were incorporated as an initial model. Two horizontal geophone component data, then, were polarization filtered and rotated to make radial component section. Traveltimes of main S-wave events were picked and used for forward modeling incorporating Poisson's ratio. This modeling provides S-wave profiles and Poisson's ratio profiles at every OBS site. The results shows that P-wave velocities in most OBS sites decrease beneath the BSR, whereas S-wave velocities slightly increase. Consequently, Poisson's ratio decreased strongly beneath the BSR indicating the presence of a free gas layer under the BSR.

Seismic Imaging of a Tidal Flat: A Case Study for the Mineopo Area (조간대(갯벌)에서의 탄성파 탐사: 민어포 지역의 사례)

  • Jou, Hyeong-Tae;Kim, Han-Joon;Lee, Gwang-Hoon;Lee, Sang-Hoon;Jung, Baek-Hoon;Cho, Hyun-Moo;Jang, Nam-Do
    • Geophysics and Geophysical Exploration
    • /
    • v.11 no.3
    • /
    • pp.197-203
    • /
    • 2008
  • A shallow high-resolution seismic reflection survey was carried out at the Mineopo tidal flat on the western coast of Korea. The purpose of the survey was to investigate shallow sedimentary structure of the tidal flat associated with the recent sea level change. A total of 795 shots were generated at 1 m interval from a 5-kg hammer source and recorded on 48 channels of 100 Hz geophones along two mutually perpendicular profiles. The water-saturated ground condition resulted in suppressed ground rolls by significantly decreasing rigidity. In addition, seismic velocities over 1500 m/s provided easy segregation of reflected arrivals from lower velocity noise. As a consequence, seismic sections from the study area show significantly higher resolution and signal to noise ratio than conventional land seismic sections. The tidal flat consists of 5 sedimentary sequences above acoustic basement. The seismic sections reveal the continuous structure of the tidal flat formed in association with sea level rise during the Holocene.

Seismic reflection survey in a tidal flat: A case study for the Mineopo area (갯벌 지역에서의 탄성파 탐사: 민어포 조간대 지역의 사례)

  • Jou Hyeong-Tae;Kim Han-Joon;Lee Gwang-Hoon;Choi Dong-Lim;Kim Min-Ji;Cho Hyun-Moo
    • 한국지구물리탐사학회:학술대회논문집
    • /
    • 2002.09a
    • /
    • pp.67-84
    • /
    • 2002
  • A shallow high-resolution seismic reflection survey was carried out at the Mineopo tidal flat on the western coast of Korea. The purpose of the survey was to investigate shallow sedimentary structure of the tidal (fat associated with the recent sea level change. A total of 795 shots were generated at 1 m interval from a 5-kg hammer source and recorded on 48 channels of 100 Hz geophones along two mutually perpendicular profiles. The water-saturated ground condition resulted in suppressed ground rolls by significantly decreasing rigidity. In addition, seismic velocities over 1500 m/s provided easy segregation of reflected arrivals from lower velocity noise. As a consequence, seismic sections were created that are high in resolution and signal to noise ratio as well. The stack sections show that the tidal flat consists of 5 sedimentary sequences above acoustic basement. Although deposition is largely characterized by the transgressive sedimentary facies resulting from sea level rise, erosional surfaces are well-resolved within the sequences.

  • PDF

A strategy to enhance the efficiency of land seismic reflection method via controlling seismic energy radiation pattern. (지면 탄성파 반사법의 효율성 향상을 위한 탄성파 발생원 에너지 방사형 변조기법)

  • Kim, Jung-Yul;Kim, Yoo-Sung
    • Proceedings of the Korean Geotechical Society Conference
    • /
    • 2004.03b
    • /
    • pp.807-814
    • /
    • 2004
  • Land seismic reflection survey has been increasingly demanded in various civil engineering works because of its own ability to delineate layers, water table, to detect cavities or fracture zones, to estimate seismic velocities of each layer. However, our shallow subsurface structures are very complex. The relatively thin layer(mostly soil) to the wavelength directly followed by a basic rock with high impedance used to generate complicated surface waves, kind of channel waves with high amplitude that is dominate in entire seismograms and hence the useful reflection events will be almost hopelessly immersed in the undesired surface waves. Thus, it would seem that the use of traditional seismic survey could not be likely to provide in itself a satisfactory information about our exploration targets. This paper hence introduces an efficient measuring strategy illustrating a properly controlled arrangement of the vertical single force sources commonly used, yielding a very sharply elongated form of P-energy with a minimum of S radiation energy, what we call, P-beam source. Abundant experiments of physical modeling showed that in that way the surface waves could be enormously reduced and the reflection events would be additive and thus reinforced. Examples of field data are also illustrated. The contribution of P-beam source will be great in civil engineering area as well as in general geological exploration area.

  • PDF

Surface geophysical surveys the northern part of the Yongdong basin (Cretaceous), Korea (영동분지(백악기) 북부 지역에 대한 지표물리탐사)

  • Kim, Ji-Su;Han, Soo-Hyung;Rhee, Cheol-U;Kim, Bok-Cheol;Ryang, U-Heon
    • Journal of the Korean Geophysical Society
    • /
    • v.5 no.4
    • /
    • pp.329-336
    • /
    • 2002
  • Electrical resistivity dipole-dipole, seismic refraction, and seismic reflection methods were performed to delineate the boundaries the Yongdong basin(Cretaceous) in terms of physical properties and to ultimately identify the margin architectures of the faults or unconformities. Higer resistivities (approximately >2000 ohm-m) most likely originate from the basement of the basin, contrasting with the lower resistivities from infilled sedimentary rocks. Faults at the eastern margin and unconformities at the western boundary are characterized as high-slope($70^{\circ}$) and gentle-slope($30^{\circ}$) gradients in the resistivity sections, respectively Such features for the boundaries are also suggested by the lower values of seismic velocity and resistivity for the western margin.

  • PDF

A case study of 3D seismic reflection imaging in an area of ground subsidence (지반 침하지역에서의 3차원 탄성파 반사법에 의한 지하구조 영상화 사례)

  • Ko, Kwang-Beom;Lee, Doo-Sung
    • 한국지구물리탐사학회:학술대회논문집
    • /
    • 2000.09a
    • /
    • pp.158-172
    • /
    • 2000
  • In order to visualize mine cavities, 3D seismic reflection data were acquired at the ground subsidence sites near Nampung coal mine area, Neukguri, Dogye, Samchuck. Full range 3D array with complete range of azimuths on the bins was considered in the data acquisition design. Because of poor S/N data, we estimated the stacking velocities by CVS method, and we estimated the shot and receiver statics on the shot and receiver stack data. We could confirm that features of ground collapse that were expected from the subsidence. In order to visualize the cavities, we need to apply more sophisticated processing schemes, such as velocity analysis, residual statics correction.

  • PDF

The Application of Geophysical Prospecting for Detecting Substructure and Boundary of Layer In Limestone Area (석회암 지역의 기반암 및 경계면 조사를 위한 지구물리 탐사법의 적용)

  • Suh, Beak-Su;Lee, Duk-Jae
    • Journal of Industrial Technology
    • /
    • v.20 no.A
    • /
    • pp.285-293
    • /
    • 2000
  • In 1970's, the analysis of shallow substructure was the interests of geological engineering and environmental problems. And seismic refraction method was applied to detect those structures. From 1980's, digital electric industry is rapidly developed and high resolution prospecting equipment is supplied. And seismic reflection method is applied to achieve various data gathering and data analysis. In this study, geophysical prospecting method is applied to calculate the basic data of limestone yield production. Seismic shallow reflection method is used to detect the depth of bedrock and electrical resistivity method is used to detect of limestone layer boundary.

  • PDF