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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Geophysics and Geophysical Exploration
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Journal DOI :
Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 16, Issue 4 - Nov 2013
Volume 16, Issue 3 - Aug 2013
Volume 16, Issue 2 - May 2013
Volume 16, Issue 1 - Feb 2013
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Near-surface P- and S-wave Velocity Structures in the Vicinity of the Cheongcheon Dam
Park, Yeong Hwan ; Kim, Ki Young ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 109~118
DOI : 10.7582/GGE.2013.16.3.109
On and near the 23-m high earthen Cheongcheon dam in Boryeong City, Korea, short seismic refraction and surface-wave profiles were conducted using a 5-kg sledgehammer. From vertical and horizontal components of the seismic waves, near-surface P-wave velocities (
) and S-wave velocities (
) were derived by inverting first-arrival refraction times and dispersion curves of Rayleigh waves. Average
for the Jurassic sedimentary basement were determined to be 1650 and 950 m/s at a depth of 30 m directly beneath the dam and 1650 m/s and 940 m/s at a depth of 10 m at the toe of the dam, respectively. The dynamic Poisson's ratio for these strata were therefore in the range of 0.24 to 0.25, which is consistent with ratios for consolidated sedimentary strata. Near a 45-m borehole 152 m downstream from the dam crest, an SH tomogram indicates a refraction boundary with an average
of 870 m/s at depths of 10 ~ 12 m. At this site, the overburden comprises the upper layer with relatively constant
around 500 and 200 m/s, respectively, and the lower layer in which both
increase with depth almost linearly. The dynamic Poisson's ratios for the overburden were in the range of 0.30 to 0.43.
3D Modeling and Inversion of Magnetic Anomalies
Cho, In-Ky ; Kang, Hye-Jin ; Lee, Keun-Soo ; Ko, Kwang-Beom ; Kim, Jong-Nam ; You, Young-June ; Han, Kyeong-Soo ; Shin, Hong-Jun ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 119~130
DOI : 10.7582/GGE.2013.16.3.119
We developed a method for inverting magnetic data to recover the 3D susceptibility models. The major difficulty in the inversion of the potential data is the non-uniqueness and the vast computing time. The insufficient number of data compared with that of inversion blocks intensifies the non-uniqueness problem. Furthermore, there is poor depth resolution inherent in magnetic data. To overcome this non-uniqueness problem, we propose a resolution model constraint that imposes large penalty on the model parameter with good resolution; on the other hand, small penalty on the model parameter with poor resolution. Using this model constraint, the model parameter with a poor resolution can be effectively resolved. Moreover, the wavelet transform and parallel solving were introduced to save the computing time. Through the wavelet transform, a large system matrix was transformed to a sparse matrix and solved by a parallel linear equation solver. This procedure is able to enormously save the computing time for the 3D inversion of magnetic data. The developed inversion algorithm is applied to the inversion of the synthetic data for typical models of magnetic anomalies and real airborne data obtained at the Geumsan area of Korea.
2D Inversion of Magnetic Data using Resolution Model Constraint
Cho, In-Ky ; Kang, Hye-Jin ; Lee, Keun-Soo ; Ko, Kwang-Beom ; Kim, Jong-Nam ; You, Young-June ; Han, Kyeong-Soo ; Shin, Hong-Jun ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 131~138
DOI : 10.7582/GGE.2013.16.3.131
We developed a method for inverting magnetic data to image 2D susceptibility models. The major difficulty in the inversion of the potential data is the nonuniqueness. Furthermore, generally the number of inversion blocks are greater than the number of the magnetic data available, and thus the magnetic inversion leads to under-determined problem, which aggravates the nonuniqueness. When the magnetic data were inverted by the general least-squares method, the anomalous susceptibility would be concentrated near the surface in the inverted section. To overcome this nonuniqueness problem, we propose a new resolution model constraint that is calculated from the parameter resolution. The model constraint imposes large penalty on the model parameter with good resolution, on the other hand small penalty on the model parameter with poor resolution. Thus, the deep-seated model parameter, generally having poor resolution, can be effectively resolved. The developed inversion algorithm is applied to the inversion of the synthetic data for typical models of magnetic anomalies and is tested on real airborne data obtained at the Okcheon belt of Korea.
A Scheme for Computing Time-domain Electromagnetic Fields of a Horizontally Layered Earth
Jang, Hangilro ; Kim, Hee Joon ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 139~144
DOI : 10.7582/GGE.2013.16.3.139
A computer program has been developed to estimate time-domain electromagnetic (EM) responses for a onedimensional model with multiple source and receiver dipoles that are finite in length. The time-domain solution can be obtained by applying an inverse fast Fourier transform (FFT) to frequency-domain fields for efficiency. Frequency-domain responses are first obtained for 10 logarithmically equidistant frequencies per decade, and then cubic spline interpolated to get the FFT input. In the case of phases, the phase curve must be made to be continuous prior to the spline interpolation. The spline interpolated data are convolved with a source current waveform prior to FFT. In this paper, only a step-off waveform is considered. This time-domain code is verified with an analytic solution and EM responses for a marine hydrocarbon reservoir model. Through these comparisons, we can confirm that the accuracy of the developed program is fairly high.
Late Quaternary Sedimentation in the Yellow Sea off Baegryeong Island, Korea
Cho, MinHee ; Lee, Eunil ; You, HakYoel ; Kang, Nyen-Gun ; Yoo, Dong-Geun ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 145~153
DOI : 10.7582/GGE.2013.16.3.145
High-resolution chirp profiles were analyzed to investigate the echo types of near-surface sediments in the Yellow Sea off the Baegryeong Island. On the basis of seafloor morphology and subbottom echo characters, 7 echo types were identified. Flat seafloor with no internal reflectors or moderately to well-developed subbottom reflectors (echo type 1-1 and 1-2) is mainly distributed in the southern part of the study area. Flat seafloor with superposed wavy bedforms (echo type 1-3) is also distributed in the middle part. Mounded seafloor with either smooth surface or superposed bedforms (echo type 2-1, 2-2, and 2-3) occurs in the middle part of the study area. Irregular and eroded seafloor with no subbottom reflectors (echo type 3-1) is present in the northern part of the study area off the Baegryeong Island. According to the distribution pattern and sedimentary facies of echo types, depositional environments can be divided into three distinctive areas: (1) active erosional zone due to strong tidal currents in the northern part; (2) formation of tidal sand ridges in response to tidal currents associated with sea-level rise distributed in the middle part; and (3) transgressive sand sheets in the southern part. Such a depositional pattern, including 7 echo types, in this area reflects depositional process related to the sea-level rise and strong tidal currents during the Holocene transgression.
An Electrical Resistivity Survey for the Characterization of Alluvial Layers at Groundwater Artificial Recharge Sites
Won, Byeongho ; Shin, Jehyun ; Hwang, Seho ; Hamm, Se-Yeong ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 154~162
DOI : 10.7582/GGE.2013.16.3.154
Vertical electrical sounding and 2D electrical resistivity survey were applied for evaluating the characteristics of alluvial layers at a groundwater artificial recharge site. The fine particles in alluvial layer, main target layer of groundwater artificial recharge, may cause clogging phenomena. In this case, electrical resistivity method is an effective technique to verify the spatial distribution of low-resistivity layers, such as saturated silts and clays. On the other hand, much attention should be paid to interpret the resistivity data in unconsolidated layers, because thick clayey overburden sometimes produces a masking effect on underlying interbedded resistive sands and gravels. Considering these points, we designed 35 points arranged in a grid form for vertical electrical sounding and 10 lines for 2D electrical resistivity survey, and concentrated our effort on enhancing the vertical and horizontal resolution of resistivity images. According to the results, 15 meters thick layers consisting of sands and gravels are located in 30 meters below ground. And the spatial distribution of silts and clays are mapped, which may cause clogging. Consequently, this approach can contribute to design and determine the location and depth of injection and observation wells for groundwater artificial recharge.
Amplitude Variation Analysis for Deep Sea Seismic Data in the Ulleung Basin, East Sea
Cheong, Snons ; Kim, Youngjun ; Kim, Byungyup ; Koo, NamHyung ; Lee, Ho-Young ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 163~170
DOI : 10.7582/GGE.2013.16.3.163
The amplitude variation with offset of seismic data can detect fluids in the sediment and resolve the petrophysical properties of hydrocarbons in the subsurface. We analyzed and described the amplitude variation in deep sea seismic data obtained from the Ulleung Basin, East Sea. By inspecting seismic CDP-offset and CDP-angle gathers which show a bright reflection event, we decided a target zone for amplitude variation analysis. From the seismic angle gather at the middle of Ulleung Basin, we recognized amplitude increase or decrease versus offset on the intercept-gradient curve. Using the product attribute and Poisson's ratio change attribute computed in terms of intercept with gradient, the top and the base of gas saturated sediments were described. The area of amplitude variation suggestive of the presence of gas saturated sediments is shown at the depth of 3 s traveltime. Anomalous features of seismic amplitude in the Ulleung Basin were classified by the crossplot of intercept and gradient. The background trend of crossplot between intercept and gradient shows an inverse proportional relation that is common for wet sediments. Anomalous amplitudes of Class III fall into the first and the third quadrants on crossplots. We inferred regional gas/water saturated area with the horizontal dimension of 150 m in the Ulleung Basin by cross-section with respect to cross-plot anomaly.
Ultrasonic Velocity Measurements of Engineering Plastic Cores by Pulse-echo-overlap Method Using Cross-correlation
Lee, Sang Kyu ; Lee, Tae Jong ; Kim, Hyoung Chan ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 171~179
DOI : 10.7582/GGE.2013.16.3.171
An automated ultrasonic velocity measurement system adopting pulse-echo-overlap (PEO) method has been constructed, which is known to be a precise and versatile method. It has been applied to velocity measurements for 5 kinds of engineering plastic cores and compared to first arrival picking (FAP) method. Because it needs multiple reflected waves and waves travel at least 4 times longer than FAP, PEO has basic restriction on sample length measurable. Velocities measured by PEO showed slightly lower than that by FAP, which comes from damping and diffusive characteristics of the samples as the wave travels longer distance in PEO. PEO, however, can measure velocities automatically by cross-correlating the first echo to the second or third echo, so that it can exclude the operator-oriented errors. Once measurable, PEO shows essentially higher repeatability and reproducibility than FAP. PEO system can diminish random noises by stacking multiple measurements. If it changes the experimental conditions such as temperature, saturation and so forth, the automated PEO system in this study can be applied to monitoring the velocity changes with respect to the parameter changes.
Physical Properties of Rocks at the Gagok Skarn Deposit
Shin, Seungwook ; Park, Samgyu ; Kim, Hyoung-Rae ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 180~189
DOI : 10.7582/GGE.2013.16.3.180
Geophysical exploration is widely used to develop strategic mineral resources in the world because of its efficient method in detecting mineralized zones in the metallic ore deposit. It is important to understand the physical properties of the stratum so that geophysical data can be more accurately interpreted. This paper is to comprehend physical properties of the rock at the Gagok mine, a typical skarn deposit in Korea. Thus, laboratory tests were conducted on specimens of ore and host rocks which were collected from rock outcrops and drill cores at the Gagok mine. Using the measurement system of rock physical property, we investigated the density, magnetic susceptibility, resistivity, and spectral induced polarization. According to the results, all physical properties of specimens had wide differences depending on contents of ore minerals, which are formed by skarnization. Especially, using the chargeability and time constant from the calculated spectral induced polarization data by the Cole-Cole inversion, we could estimate the volume contents as well as the grain size of the sulfide minerals. Therefore, the spectral induced polarization technique may be considered a useful method when exploring metallic ore deposit with sulfide minerals.
Near-surface Shear-wave Velocities Derived from Microtremors and Teleseismic Data at the Hwacheon Seismic Station
Yun, Won Young ; Park, Sun-Cheon ; Kim, Ki Young ;
Geophysics and Geophysical Exploration, volume 16, issue 3, 2013, Pages 190~195
DOI : 10.7582/GGE.2013.16.3.190
We estimated near-surface shear-wave velocity (
) at the Hwacheon seismic station using a geologic log of a well, microtremors recorded during a period of 56 days, and records of three teleseismic events (
). The vs of the 10-m thick soil layer (
= 296 m/s) was determined from horizontal-to-vertical spectral ratios of microtremors recorded at the surface. The average
= 1,309 m/s) from the surface to the 96-m depth of a borehole sensor, was computed using spectral coherence analyses of data recorded by surface- and borehole-sensors for the three teleseismic events. Using these calculated values of
, the computed bedrock
is 2,150 m/s and the time-averaged
to a 30-m depth is 696 m/s. Accordingly the Hwacheon seismic station is regarded as a relatively good site. The deduced near-surface
can be used for further quantitative evaluation of site amplification and earthquake hazard.