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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Geophysics and Geophysical Exploration
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Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 9, Issue 4 - Nov 2006
Volume 9, Issue 3 - Aug 2006
Volume 9, Issue 2 - May 2006
Volume 9, Issue 1 - Feb 2006
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Seismic Properties Study of Gas Hydrate in Deep Sea using Numerical Modeling Technique
Shin, Sung-Ryul ; Yeo, Eun-Min ; Kim, Chan-Su ; Park, Keun-Pil ; Lee, Ho-Young ; Kim, Young-Jun ;
Geophysics and Geophysical Exploration, volume 9, issue 2, 2006, Pages 139~147
We had conducted a numerical modeling to investigate seismic properties of gas hydrate with field parameters acquired over the East sea in 1998. We used a 2-D staggered grid finite difference method to generate synthetic elastic seismograms for multi-channel seismic survey, OBC (Ocean Bottom Cable) survey and VCS (Vertical Cable Seismic) survey. The results of this study showed that the method using staggered grid yielded stable results and could be used to seismic imaging. We could find out the high amplitude anomaly and the phase reversal phenomenon of reflection wave at interface between the gas hydrate layer and free gas layer such a BSR (Bottom Simulating Reflector) which is the evidence for existence of gas hydrate in seismic reflection data. And we computed the reflection coefficients at the incident angles corresponding to offset distance with the synthetic seismograms. The reflection coefficients acquired from the numerical modeling were nearly consistent with the reflection coefficient computed by Shuey's equation.
A Numerical Study on the Effect of Near Surface Inhomogeneity on Rayleigh Wave Propagation and Dispersion
Lee, Sang-Min ; Park, Kwon-Gyu ; Byun, Joong-Moo ;
Geophysics and Geophysical Exploration, volume 9, issue 2, 2006, Pages 148~154
The effect of small-scale near surface inhomogeneity on Rayleigh wave propagation and dispersion has been investigated in this study using two-dimensional FEM elastic modeling. Various inhomogeneity models with a variety of geometrical shape and embedment depth which exist in homogeneous half-space and two-layered media are considered. Results show that any near surface inhomogeneity greater than one wavelength in terms of minimum wavelength of Rayleigh wave shows dispersion characteristics. Such dispersion effect become stronger as the dimensions of the inhomogeneity increase. The effect of horizontal dimension is more dominant factor governing the dispersion characteristics than vertical dimension. However, the dispersion effect can not be identifiable in seismogram if the horizontal dimension is not wide enough. Nonetheless, even in this case, the existence of inhomogeneity can be inferred by the reflection or transmission event of Rayleigh wave. The results can be expected to provide insights on the behavior of Rayleigh wave which may be helpful for designating field work or new processing scheme to detect near surface inhomogeneity by surface wave method.
Safety Index Evaluation from Resistivity Monitoring Data for a Reservoir Dyke
Cho, In-Ky ; Kang, Hyung-Jae ; Lee, Byoung-Ho ; Kim, Byoung-Ho ; Yi, Sang-Sun ; Park, Young-Gyu ; Lee, Bo-Hyun ;
Geophysics and Geophysical Exploration, volume 9, issue 2, 2006, Pages 155~162
An abnormal seepage flow, which is mainly caused by the piping, is one of the major reasons for embankment dam failure. A leakage detection is therefore a vital part of an embankment dam's monitoring. Resistivity method, which is an efficient tool to detect leakage zones, has been used all over the world for an embankment dam's monitoring. Although the resistivity method gives us very useful information about the leakage problem, there is no more quantitative interpretation than the low resistivity zones in the 2-dimensional resistivity section are regraded simply as the anomalous seepage zones. Recently, resistivity monitoring technique is applied for the detection of leakage zones. However, its interpretation still remains in the stage of presenting the resistivity ratio itself. An increased seepage flow increases a porosity and an increasing porosity decreases the dam's stability. Therefore, the porosity is one of the major factors for an embankment dam's stability. Based on Archie's experimental formula, we try to evaluate a porosity distribution from the resistivity data which is obtained on the dam's crest. We also attempt to represent a procedure to evaluate a safety index of the embankment dam from the resistivity monitoring data.
Marine Controlled-source Electromagnetic Surveys for Hydrocarbon Exploration
Kim, Hee-Joon ; Han, Nu-Ree ; Choi, Ji-Hyang ; Nam, Myung-Jin ; Song, Yoon-Ho ; Suh, Jung-Hee ;
Geophysics and Geophysical Exploration, volume 9, issue 2, 2006, Pages 163~170
The shortage of proven hydrocarbon reserves has resulted in exploration progressing from the offshore into progressively deeper water of the continental shelf. Despite the success of seismic acquisition at ever greater depths, there are marine geological terrenes in which the interpretation of seismic data is difficult, such regions dominated by scattering or high reflectivity that is characteristic of carbonate reefs, volcanic cover and submarine permafrost. A marine controlled-source electromagnetic (CSEM) method has recently been applied to the oil and gas exploration thanks to its high-resistivity characteristics of the hydrocarbon. In particular, this method produces better results in terms of sensitivity under the deep water environment rather than the shallow water. Only in the last five years has the relevance of CSEM been recognized by oil companies who now use it to help them make exploration drilling decisions. Initial results are most promising and several contractors now offer magnetotelluric and CSEM services.
Comments on Gravity Reduction and Gravity Anomaly
Park, Yeong-Sue ; Lim, Mu-Taek ; Rim, Hyoung-Rae ;
Geophysics and Geophysical Exploration, volume 9, issue 2, 2006, Pages 171~175
Gravity reduction and Bouguer anomaly are frequently misunderstood by many geoscientists as follows; the observed gravity is reduced to a common datum plane, so that gravity effects by all materials above the datum is removed, therefore, Bouguer anomaly is located on the datum plane. In reality, Bouguer anomaly does not lie on a common datum plane, but is difference between observed gravity and reference gravity at the actual point of measurement. Commonly used gravity reduction formulas are approximate formulas. Here, we introduce complete formulas, and suggest to use them for more accurate results. We also suggest to use not the geoid but the reference ellipsoid as the vertical datum.