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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Geophysics and Geophysical Exploration
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Journal DOI :
Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 6, Issue 4 - Nov 2003
Volume 6, Issue 3 - Aug 2003
Volume 6, Issue 2 - May 2003
Volume 6, Issue 1 - Feb 2003
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Frequency Sounding in Small-Loop EM Surveys
Cho In-Ky ; Lim Jin-Taik ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 119~125
The small-loop electromagnetic (EM) technique has been used successfully for many geophysical investigations, particularly for shallow engineering and environmental surveys. In conventional small loop EM operating at small induction numbers, geometric sounding has been widely used because the depth of penetration of EM energy depends only on the source-receiver separation. Recently developed small loop EM system, however, measures the secondary magnetic field,
, at multiple frequencies with a fixed source-receiver separation and frequency sounding is tried actively. In this study, we analyzed the behavior of in-phase and quadrature components of
, for horizonal coplanar (HCP) configuration over two-layer models. Through this theoretical analysis, it was found that the in-phase component of
is more suitable for frequency sounding than the quadrature component. But, the in-phase component of
is too small to measure, especially in resistive and noisy environment like Korea. Using the fact that the quadrature component is much greater than the in-phase component and the difference of quadrature component of
measured at two frequencies shows the same behavoir as the in-phase component, we suggested an alternative frequency sounding technique. Also, we defined an apparent conductivity, which reflects well the conductivity of subsurface layers.
Resolution of Shallow Marine Subsuface Structure Image Associated with Acquisition Parameters of High-resolution Multi-channel Seismic Data
Lee Ho-Young ; Koo Nam-Hyung ; Park Keun-Pil ; Yoo Dong-Geun ; Kang Dong-Hyo ; Kim Young-Gun ; Seo Gab-Seok ; Hwang Kyu-Duk ; Kim Jong-Chon ; Kim Ji-Soo ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 126~133
High-resolution shallow marine seismic surveys have been carried out for the resources exploration, engineering applications and Quaternary mapping. To improve the resolution of subsurface structure image, multichannel digital technique has been applied. The quality of the image depends on the vertical and horizontal resolution and signal to noise (S/N) ratio which are associated with the data acquisition parameters such as sample interval, common midpoint (CMP) interval and CMP fold. To understand the effect of the acquisition parameters, a test survey was carried out off Yeosu and the acquired data were analyzed. A 30
small air gun was used as a seismic source and 8 channel streamer cable with a 5 m group interval was used as a receiver. The data were digitally recorded with a shot interval of 2 s and sample interval of 0.1 ms. The acquired data were resampled with various sample intervals, CMP intervals and CMP folds. The resampled data were processed, plotted as seismic sections and compared each other. The analysis results show that thin bed structure with
slope can be imaged with good resolution and continuity and low noise using the acquisition parameters with a sample interval shorter than 0.2 ms, CMP interval shorter than 2.5 m and CMP fold more than 4. Because seismic resolution is associated with the acquisition parameters, the quality of the subsurface structure can be imaged successfully using suitable and optimum acquisition parameters.
Seismic Trace Interpolation using Spectral Estimation
Ji Jun ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 134~137
A scheme for missing-trace interpolation of linear events is proposed. For a two-dimensional seismic dataset which contains linear events, a post-interpolation spectrum can be estimated from a portion of the original aliased spectrum. The restoration of missing trace data is accomplished by minimizing the energy after applying a filter which has an amplitude spectrum that is inverse to the estimated spectrum.
A Study for the Construction of the P and S Velocity Tomogram from the Crosswell Seismic Data Generated by an Impulsive Source
Lee, Doo-Sung ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 138~142
Crosswell seismic data were acquired in three sections crossing a tunnel of 3 different types; one was empty, another was ailed by sand, and the other was filled by rock debris. Both the P- and S-wave first arrivals were picked and the traveltime tomography was conducted to generate the P- and S- wave velocity tomograms on the all three sections. Among six tomograms, only one tomogram shows a low velocity zone that can be interpreted as a tunnel image. The tomogram is the P wave velocity image of a section that crosses an empty tunnel. The result of numerical analysis for the spatial resolution of the traveltime tomography was consistent to this finding.
Application of Electrical and Small-Loop EM survey to the Identification of the Leachate at a Waste Landfill in Jeiu Island
Song Sung-Ho ; Yong Hwan-Ho ; An Jung-Gi ; Kim Gee-Pyo ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 143~152
Among the various geophysical approaches to identify the leakage of leachate with conductivity variation, conventional electrical resistivity survey has been mainly used at waste landfill. We adopted small-loop electromagnetic (EM) survey using multi-frequencies in parallel with electrical resistivity survey to delineate the leakage of leachate through the shallow soil layer at a waste landfill in Jeju Island, and also with self-potential monitoring to detect the streaming potential produced by the movement of leachate. There were no evidences of leakage from waste landfill according to the results of the electrical resistivity survey and SP monitoring, and it was also true from the results of water quality analysis at stream around waste landfill periodically. On the other hand, the results of one-dimensional inversion of spatially-filtered small-loop EM survey data showed the anomalous zone of low resistivity with depth both around and inner waste landfill.
Improvement of Reverse-time Migration using Modified Receiver Aperture
Cheong Soon-Hong ; Shin Chang-Soo ;
Geophysics and Geophysical Exploration, volume 6, issue 3, 2003, Pages 153~159
Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.