• Title/Summary/Keyword: travel time tomography

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A Study on the Static Correction for the First Arrival Travel-time of the Cross-well Seismic Data (시추공 탄성파 초동주시 기록의 정보정 연구)

  • Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.14 no.2
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    • pp.146-151
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    • 2011
  • A method to evaluate and to reduce the source- and receiver- consistent noise in a cross-well travel time data was proposed. These systematic noises, which can cause some serious effects on the result of a travel time tomography, can be considered as the source and receiver statics. The method evaluates the statics through a curve-fitting of the first arrival travel times in the common source and common receiver gathers. Feasibility study was conducted on a synthetic data which simulates the cross-well travel time tomography to detect a small scale tunnel in a uniform background medium. First arrival travel times at a given source and receiver points are computed by a raytracing method, and the source consistent- and receiver consistent noises are added to the record. In case of the added noise with rms amounting to 25% of the maximum expected anomalous travel time delays, it is confirmed that the method successfully extracted the noise at the 7th step of iteration.

A Study on the Reliability Evaluation of the Cross-well Seismic Travel-time Tomography (시추공 탄성파 주시 토모그래피의 신뢰도 평가에 관한 연구)

  • Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.13 no.4
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    • pp.330-335
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    • 2010
  • In order to estimate the confidence level of the velocity distribution shown in a velocity image reconstructed from a travel-time tomography, the ray coverage and the inversion characteristics of the system matrix were investigated. The targets of the analysis is the first arrival travel-time, the raypath information, and the resulting velocity model. The ray coverage, degree of ray and model coupling, was estimated by the number of rays and total ray length in a velocity grid, and information regarding the resolution and uncertainties involved in the reconstructed velocity model was derived from the results of the SVD analysis of the system matrix that relates the data space (first arrival travel times) to the model space (velocity distribution in tomogram).

Field Application of 3D seismic travel-time tomography (3차원 탄성파 지대공 토모그래피 현장 적용)

  • Moon, Yun-Seop;Ha, Hee-Sang;Lim, Harry;Ko, Kwang-Beom
    • 한국지구물리탐사학회:학술대회논문집
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    • 2006.06a
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    • pp.233-237
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    • 2006
  • 3D travel time tomography was conducted to characterize the subsuface structure in the valley area. In this study, an area($200m{\times}200m$), where borehole informations were available to aid in the interpretation, was covered with wide source/receiver coverage. In data acquisition, both hole to hole and reverse VSP array was employed. For the inversion, 3D seismic traveltime tomography algorithm based on Fresnel volume was implemented. When compared 3D velocity cube with the geological survey and drilling logs, both results were matched well. From this, we concluded that 3D seismic travel time tomography has enough potential to the field application.

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3D Seismic Travel-time Tomography using Fresnel Volume (프레넬 볼륨을 이용한 3차원 탄성파 주시 토모그래피)

  • Ko, Kwang-Beom;Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.6 no.2
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    • pp.101-107
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    • 2003
  • 3D seismic travel-time tomography algorithm baled on Fresnel volume was developed and its feasibility was investigated by the numerical experiments. To testify the field applicability of the developed algorithm, frequency characteristics and way coverage of the crossholel seismic raw data were investigated and 3D velocity tomogram cube with about 8m spatial resolution was obtained. When compared this 3D velocity cube with the conventional 2D ray tomogram, two results were matched well. We concluded that 3D seismic tomography algorithm developed in this study has enough potential to the field application.

TRAVEL TIME TOMOGRAPHY

  • Uhlmann, Gunther
    • Journal of the Korean Mathematical Society
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    • v.38 no.4
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    • pp.711-722
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    • 2001
  • We survey recent results on the inverse kinematic problem arising in geophysics. The question is whether one can determine the sound speed (index of refraction) of a medium by measuring the travel times of the corresponding ray paths. We emphasize the anisotrpic case.

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Travel Time Calculation Using Mono-Chromatic Oneway Wave Equation (단일주파수 일방향파동방정식을 이용한 주시계산)

  • Shin, Chang-Soo;Shin, Sung-Ryul;Kim, Won-Sik;Ko, Seung-Won;Yoo, Hai-Soo
    • Geophysics and Geophysical Exploration
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    • v.3 no.4
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    • pp.119-124
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    • 2000
  • A new fast algorithm for travel time calculation using mono-chromatic one-way wave equation was developed based on the delta function and the logarithms of the single frequency wavefield in the frequency domain. We found an empirical relation between grid spacing and frequency by trial and error method such that we can minimize travel time error. In comparison with other methods, travel time contours obtained by solving eikonal equation and the wave front edge of the snapshot by the finite difference modeling solution agree with our algorithm. Compared to the other two methods, this algorithm computes travel time of directly transmitted wave. We demonstrated our algorithm on migration so that we obtained good section showing good agreement with original model. our results show that this new algorithm is a faster travel time calculation method of the directly transmitted wave for imaging the subsurface and the transmission tomography.

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Development and Application of a Seismic Tomography Software Based on Windows (탄성파 토모그래피 자동화 처리 소프트웨어 개발 및 적용성 검토)

  • Jung, Sang-Won;Ha, Hee-Sang;Ko, Kwang-Beom
    • Geophysics and Geophysical Exploration
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    • v.7 no.3
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    • pp.157-163
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    • 2004
  • In this study, a travel-time tomography software was developed under the MS Windows system and GUI environment for user. The software supports following features: (1) supporting various data input format (2) flexible treatment of shot and receiver coordinate coding (3) flexible first arrival picking and modification (4) easy modification of intermediate tomogram. It is expected that the effort of the user can be minimized in each data processing step.

Joint Inversion of DC Resistivity and Travel Time Tomography Data (전기비저항과 주시 토모그래피 탐사자료의 복합역산)

  • Kim, Jung-Ho;Yi, Myeong-Jong;Park, Kwon-Gyu;Cho, Chang-Soo
    • 한국지구물리탐사학회:학술대회논문집
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    • 2007.06a
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    • pp.58-63
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    • 2007
  • We developed a new algorithm for jointly inverting dc resistivity and seismic travel time tomography data based on the multiple constraints: (1) structural similarity based on cross-gradient, (2) correlation between two different material properties, and (3) a priori information on the material property distribution. Through the numerical experiments of surface dc resistivity and seismic refraction surveys, the performance of the proposed algorithm was demonstrated and the effects of different regularizations were analyzed.

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An Analysis of the Noise Influence on the Cross-well Travel-time Tomography to Detect a Small Scale Low Velocity Body (소규모 저속도 이상대 탐지를 위한 시추공 주시 토모그래피에서 잡음 영향 분석)

  • Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.14 no.2
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    • pp.140-145
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    • 2011
  • In order to analyze the influence of the noise on a cross-well traveltime tomography to detect a small scale low velocity body in a homogeneous medium, the first arrival travel times were computed one a tunnel model by a finite-difference ray tracing scheme. Three different types and four different intensity levels of white noises were added to the computed first arrival travel times, and velocity tomograms were constructed using an iterative inversion method (SIRT). Tomograms with the noise intensity up to 10% of the maximum traveltime delay in the tunnel model, showed the exact location of the tunnel. However, the velocity shown at the tunnel location was not close to air velocity but only slightly less than the velocity of the background medium. The additive random noise showed significantly less degree of influence on the resulting tomogram than the source- and receiver consistent noise.

Evaluation of near surface Vs distribution by using SPT uphole method (SPT 업홀기법을 이용한 지반의 2차원 전단파 속도 분포 도출)

  • Kim, Dong-Soo;Bang, Eun-Seo;Kim, Jong-Tae
    • 한국지구물리탐사학회:학술대회논문집
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    • 2005.09a
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    • pp.93-116
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    • 2005
  • SPT-Uphole tomography method was introducedand verified in this paper. In SPT-Uphole method, SPT (Standard Penetration Test) which is common in site investigation, was used as a source and several surface geophones in line were used as receivers. Shear wave velocity (Vs) distribution map which has triangular shape around the boring point can be obtained by tomography inversion. The factors for obtaining reliable result of SPT-Uphole tomography are exact travel time information and accurate inversion method. To establish of the SPT-Uphole tomography procedure, the most reliable method for obtaining exact travel time information and verification of tomography inversion method were studied by using theoretical travel time information and finite element method (FEM) analysis. finally, SPT-Uphole tomography method was performed at the weathered soil site in Kimje. By comparing with several boring data including SPT-N value, feasibility of this method was verified in the field.

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