• Title/Summary/Keyword: 탄성파 음원

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Detailed Processing and Analysis on the Single-channel Seismic Data for Site Survey of Daecheon-Wonsando Subsea Tunnel (대천-원산도 해저터널 부지조사를 위한 단일채널 탄성파자료의 정밀 처리 및 분석)

  • Kim, Won-Sik;Park, Keun-Pil;Kim, Hyun-Do;Cheong, Snons;Koo, Nam-Hyung;Lee, Ho-Young;Park, Eui-Seob
    • Geophysics and Geophysical Exploration
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    • v.13 no.4
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    • pp.336-348
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    • 2010
  • The Single-channel seismic survey with the source of bubble pulser and drilling survey was carried out in 2008 and 2009 for the site survey of Daecheon-Wonsando area, which was a proposed area of Korea-China subsea tunnel. The goal of this study is to analyze the depth and characteristics of acoustic basement for the stability assessment and tunnel design in this proposed area through combining drilling data with this single-channel seismic data after detailed processing. For this purpose, among the data processing schemes which are usually applied to multi-channel seismic data, we applied the F-K filtering to eliminate the AC(alternating current) noise and the post-stack depth migration to produce depth section. As a result, we verified that the improved depth section could be obtained from single-channel seismic data, and the distribution and characteristics of basement could be analyzed in survey area through the combined analysis with drilling data. However, we could not interpret the detailed structures, fault and fracture zone, due to the quality of bubble pulser source and single-channel data. We expect that those detailed structures can be analyzed when higher resolution seismic data is provided. Therefore, we recommend some items for future seismic survey of subsea tunnel to obtain the high resolution seismic data.

Applying Spitz Trace Interpolation Algorithm for Seismic Data (탄성파 자료를 이용한 Spitz 보간 알고리즘의 적용)

  • Yang Jung Ah;Suh Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.6 no.4
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    • pp.171-179
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    • 2003
  • In land and marine seismic survey, we generally set receivers with equal interval suppose that sampling interval Is too narrow. But the cost of seismic data acquisition and that of data processing are much higher, therefore we should design proper receiver interval. Spatial aliasing can be occurred on seismic data when sampling interval is too coarse. If we Process spatial aliasing data, we can not obtain a good imaging result. Trace interpolation is used to improve the quality of multichannel seismic data processing. In this study, we applied the Spitz algorithm which is widely used in seismic data processing. This algorithm works well regardless of dip information of the complex underground structure. Using prediction filter and original traces with linear event we interpolated in f-x domain. We confirm our algorithm by examining for some synthetic data and marine data. After interpolation, we could find that receiver intervals get more narrow and the number of receiver is increased. We also could see that continuity of traces is more linear than before Applying this interpolation algorithm on seismic data with spatial aliasing, we may obtain a better migration imaging.

Investigation and Processing of Seismic Reflection Data Collected from a Water-Land Area Using a Land Nodal Airgun System (수륙 경계지역에서 얻어진 육상 노달 에어건 탄성파탐사 자료의 고찰 및 자료처리)

  • Lee, Donghoon;Jang, Seonghyung;Kang, Nyeonkeon;Kim, Hyun-do;Kim, Kwansoo;Kim, Ji-Soo
    • The Journal of Engineering Geology
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    • v.31 no.4
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    • pp.603-620
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    • 2021
  • A land nodal seismic system was employed to acquire seismic reflection data using stand-alone cable-free receivers in a land-river area. Acquiring reliable data using this technology is very cost effective, as it avoids topographic problems in the deployment and collection of receivers. The land nodal airgun system deployed on the mouth of the Hyungsan River (in Pohang, Gyeongsangbuk Province) used airgun sources in the river and receivers on the riverbank, with subparallel source and receiver lines, approximately 120 m-spaced. Seismic data collected on the riverbank are characterized by a low signal-to-noise (S/N) and inconsistent reflection events. Most of the events are represented by hyperbola in the field records, including direct waves, guided waves, air waves, and Scholte surface waves, in contrast to the straight lines in the data collected conventionally where source and receiver lines are coincident. The processing strategy included enhancing the signal behind the low-frequency large-amplitude noise with a cascaded application of bandpass and f-k filters for the attenuation of air waves. Static time delays caused by the cross-offset distance between sources and receivers are corrected, with a focus on mapping the shallow reflections obscured by guided wave and air wave noise. A new time-distance equation and curve for direct and air waves are suggested for the correction of the static time delay caused by the cross-offset between source and receiver. Investigation of the minimum cross-offset gathers shows well-aligned shallow reflections around 200 ms after time-shift correction. This time-delay static correction based on the direct wave is found essential to improving the data from parallel source and receiver lines. Data acquisition and processing strategies developed in this study for land nodal airgun seismic systems will be readily applicable to seismic data from land-sea areas when high-resolution signal data becomes available in the future for investigation of shallow gas reservoirs, faults, and engineering designs for the development of coastal areas.

Spectral Analysis of Transient Elastic Waves Generated by Point Source in Glass and Unidirectional CFRP Plates (유리판과 단일방향 탄소섬유강화 플라스틱판에서 점원에 의해 발생된 과도적 탄성파의 주파수 해석)

  • Lee, Jeong-Ki;Kim, Ho-Chul;Choi, Myoung-Seon;Kim, Young-Hwan
    • The Journal of the Acoustical Society of Korea
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    • v.13 no.6
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    • pp.50-59
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    • 1994
  • Spectral analysis of transient elastic waves were carried out in order to identify the propagation modes in glass and unidirectional carbon fibre reinforced plastic (CFRP) plates. Pencil leads were broken on the surface of plates to generate elastic waves, and two broad band transducers of 6.35 mm in diameter and 10 MHz center frequency were placed at the linear location from the source. The frequency spectra of detected signals showed that the wave propagation in the plates obeyed the Lamb wave dispersion relation. The transient signals were the fast propagating modes around maximum group velocity of the lowest and first order symmetric $modes(S_{0} and S_{1}),$ and first order antisymmetric $mode(A_{1})$. The transient signals were not severely distorted due to relatively small dispersion of those modes around the maximum group velocity. The fastest propagating mode in the plates was shown to be $S_{0}$ mode less the than cut-off frequency of $A_{1}$ mode.

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Geophysical Investigation of Gas Hydrate-Bearing Sediments in the Sea of Okhotsk (오호츠크해 가스하이드레이트 퇴적층의 지구물리 탐사)

  • Jin, YoungKeun;Chung, KyungHo;Kim, YeaDong
    • Journal of the Korean Geophysical Society
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    • v.7 no.3
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    • pp.207-215
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    • 2004
  • As the sea connecting with the East Sea, the Sea of Okhotsk is the most potential area of gas hydrates in the world. In other to examine geophysical structures of gas hydrate-bearing sediments in the Sea of Okhotsk, the CHAOS (hydro-Carbon Hydrate Accumulation in the Okhotsk) international research expedition was carried out in August 2003. In the expedition, high-resolution seismic and geochemical survey was also conducted. Sparker seismic profiles show only diffusive high-amplitude reflections without BSRs at BSR depth. It means that BSR appears to be completely different images on seismic profiles obtained using different frequencies. Many gas chimneys rise up from BSR depth to seafloor. The chimneys can be divided into two groups with different seismic characteristics; wipe-out (WO) and enhanced reflection (ER) chimneys. Different seismic responses in the chimneys would be caused by amount of gas and gas hydrates filling in the chimneys. In hydroacoustic data, a lot of gas flares rise up several hundreds meters from seafloor to the water column. All flares took placed at the depths within gas hydrate stability zone. It is interpreted that gas hydrate-bearing sediments with low porosity and permeability due to gas hydrate filling in the pore space make good pipe around gas chimneys in which gas is migrating up without loss of amount. Therefore, large-scale gas flare at the site on gas chimney releases into the water column.

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Geophysical and Geological Investigation for Selecting a Dinosaur Museum Site in the Dinosaur Egg Fossil Area, Gojeong-ri, Hwasung, Gyeonggi Province (경기도 화성 고정리 공룡알 화석지 공룡생태박물관 부지선정을 위한 지구물리 및 지질조사)

  • Kim, Han-Joon;Jeong, Gap-Sik;Yi, Bo-Yeon;Jo, Churl-Hyun;Lee, Kwang-Bae;Lee, Jun-Ho;Jou, Hyeong-Tae;Lee, Gwang-Hoon
    • Geophysics and Geophysical Exploration
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    • v.13 no.4
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    • pp.357-363
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    • 2010
  • In this study, we investigated the geologic structure of the basement and overlying sediments of the construction site of the dinosaur egg fossil museum in Hwasung, Gyeonggi Province through refraction seismology, drilling, and downward seismic velocity measurements in the drill holes. The construction site ($350{\times}750\;m^2$) is located in the reclaimed area south of Sihwa Lake, Gojeong-ri. About 6,950 m of seismic refraction data consisting of 11 lines were acquired using a sledge hammer source. Drilling to the basement was performed at five sites. Sediment samples from drilling were analysed for grain-size distribution and age dating. At two drill holes, seismic velocity was measured with depth using a hammer as a seismic source. The geological structure of the study area consists of, from top to bottom, a tidal flat layer (5 ~ 12 m thick), a weathered soil layer (2 ~ 8 m thick), and the basement. The basement is interpreted as Cretaceous sedimentary rocks that tend to be shallow eastward. The volume of the tidal flat sediments and weathered soil in the study area is estimated as $1.4{\times}10^6\;m^3$, weighing $3.5{\times}10^6$ tons. The rate of sea level rise since 8,000 yrs BP is estimated to be 0.1 ~ 0.15 cm/yr.

A Study on the Field Data Applicability of Seismic Data Processing using Open-source Software (Madagascar) (오픈-소스 자료처리 기술개발 소프트웨어(Madagascar)를 이용한 탄성파 현장자료 전산처리 적용성 연구)

  • Son, Woohyun;Kim, Byoung-yeop
    • Geophysics and Geophysical Exploration
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    • v.21 no.3
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    • pp.171-182
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    • 2018
  • We performed the seismic field data processing using an open-source software (Madagascar) to verify if it is applicable to processing of field data, which has low signal-to-noise ratio and high uncertainties in velocities. The Madagascar, based on Python, is usually supposed to be better in the development of processing technologies due to its capabilities of multidimensional data analysis and reproducibility. However, this open-source software has not been widely used so far for field data processing because of complicated interfaces and data structure system. To verify the effectiveness of the Madagascar software on field data, we applied it to a typical seismic data processing flow including data loading, geometry build-up, F-K filter, predictive deconvolution, velocity analysis, normal moveout correction, stack, and migration. The field data for the test were acquired in Gunsan Basin, Yellow Sea using a streamer consisting of 480 channels and 4 arrays of air-guns. The results at all processing step are compared with those processed with Landmark's ProMAX (SeisSpace R5000) which is a commercial processing software. Madagascar shows relatively high efficiencies in data IO and management as well as reproducibility. Additionally, it shows quick and exact calculations in some automated procedures such as stacking velocity analysis. There were no remarkable differences in the results after applying the signal enhancement flows of both software. For the deeper part of the substructure image, however, the commercial software shows better results than the open-source software. This is simply because the commercial software has various flows for de-multiple and provides interactive processing environments for delicate processing works compared to Madagascar. Considering that many researchers around the world are developing various data processing algorithms for Madagascar, we can expect that the open-source software such as Madagascar can be widely used for commercial-level processing with the strength of expandability, cost effectiveness and reproducibility.

Inverse Estimation of Geoacoustic Parameters in Shallow Water Using tight Bulb Sound Source (천해환경에서 전구음원을 이용한 지음향인자의 역추정)

  • 한주영;이성욱;나정열;김성일
    • The Journal of the Acoustical Society of Korea
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    • v.23 no.1
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    • pp.8-16
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    • 2004
  • An inversion method is presented for the determination of the compressional wave speed, compressional wave attenuation, thickness of the sediment layer and density as a function of depth for a horizontally stratified ocean bottom. An experiment for estimating those properties was conducted in the shallow water of South Sea in Korea. In the experiment, a light bulb implosion and the propagating sound were measured using a VLA (vertical line array). As a method for estimating the geoacoustic properties, a coherent broadband matched field processing combined with Genetic Algorithm was employed. When a time-dependent signal is very short, the Fourier transform results are not accurate, since the frequency components are not locatable in time and the windowed Fourier transform is limited by the length of the window. However, it is possible to do this using the wavelet transform a transform that yields a time-frequency representation of a signal. In this study, this transform is used to identify and extract the acoustic components from multipath time series. The inversion is formulated as an optimization problem which maximizes the cost function defined as a normalized correlation between the measured and modeled signals in the wavelet transform coefficient vector. The experiments and procedures for deploying the light bulbs and the coherent broadband inversion method are described, and the estimated geoacoustic profile in the vicinity of the VLA site is presented.

AE source on-line localization on material with unknown acoustic wave propagation velocity (전파속도를 알수 없는 재료에서의 AE 발생위치 온라인 측정)

  • Jhang, Kyung-Young;Lee, Weon-Heum;Kim, Dal-jung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.3
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    • pp.688-694
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    • 1998
  • The ability to locate the defects in materials is one of the major attrations of the acoustic emission(AE) technique. The most conventional method for planar AE source localization is to place three or more AE sensors on the plate and to determine the source position by measuring the differences in the arrival times of the AE wave at the sensors, which is called as triangulation method. But this method can not be applied in the material of which elastic wave propagtion velocity is not known. In this paper, we propose two methods, vector method and error minimization method, for AE source location on the material with unknown AE wave velocity. In this method, it is not needed to know the propagation velocity previously, that is, we can apply this method to arbitrary material of which properties are not known exactly. Also, in this paper, the robustness to the error in the measurement of time differences are discussed for both methods. Finally, in order to evaluate the actual performances, experiments using a pencil lead break as the AE source were carried out on the aluminum plate.

Three Dimensional FE Analysis of Acoustic Emission of Composite Plate (복합재료 파손 시 발생하는 음향방출의 3차원 유한요소 해석)

  • Paik, Seung-Hoon;Park, Si-Hyong;Kim, Seung Jo
    • Composites Research
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    • v.18 no.5
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    • pp.15-20
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    • 2005
  • In this paper, damage induced acoustic emission in the composite plate in numerically simulated by using the three dimensional finite element method and explicit time integration. Acoustic source is modeled by equivalent volume source. To verify the proposed method, dynamic displacements due to the elastic wave are compared with the experiment when the fiber is broken in the single fiber embedded isotropic plate. For the laminated composite plates, the results are compared between homogenized model and DNS approach which models fibers and matrix separately. To capture high frequencies in the elastic wave, small time step size and a large number of meshes are required. The parallel computing technology is introduced to solve a large scale problem efficiently.