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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 14, Issue 4 - Nov 2011
Volume 14, Issue 3 - Aug 2011
Volume 14, Issue 2 - May 2011
Volume 14, Issue 1 - Feb 2011
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High-resolution Seismic Imaging of Shallow Geology Offshore of the Korean Peninsula: Offshore Uljin
Kim, Han-Joon ; Jou, Hyeong-Tae ; Yoo, Hai-Soo ; Kim, Kwang-Hee ; You, Lee-Sun ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 127~132
We acquired and interpreted more than 650 km of high-resolution seismic reflection profiles in the Hupo Basin, offshore east coast of Korea at
in the East Sea (Japan Sea) to image shallow and basement deformation. The seismic profiles reveal that the main depocenter of the Hupo Basin in the study area is bounded by the large offset Hupo Fault on the east and an antithetic fault on the west; however, the antithetic fault is much smaller both in horizontal extension and in vertical displacement than the Hupo Fault. Sediment infill in the Hupo Basin consists of syn-rift (late Oligocene. early Miocene) and post-rift (middle Miocene.Holocene) units. The Hupo Fault and other faults newly defined in the Hupo Basin strike dominantly north and show a sense of normal displacement. Considering that the East Sea has been subjected to compression since the middle Miocene, we interpret that these normal faults were created during continental rifting in late Oligocene to early Miocene times. We suggest that the current ENE direction of maximum principal compressive stress observed in and around the Korean peninsula associated with the motion of the Amurian Plate induces the faults in the Hupo Basin to have reverse and right-lateral, strike-slip motion, when reactivated. A recent earthquake positioned on the Hupo Fault indicates that in the study area and possibly further in the eastern Korean margin, earthquakes would occur on the faults created during continental rifting in the Tertiary.
Some Theoretical Considerations in Body Tide Calculation
Na, Sung-Ho ; Shin, Young-Hong ; Baek, Jeong-Ho ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 133~139
The largest terms in the solid Earth body tide calculation are second degree spherical harmonic components due to the moon or the sun, and they compose about 98 percent of total contribution. Each degree harmonics of the tidal perturbation should be evaluated through multiplication with distinct Love numbers or their combinations. Correct evaluation of these terms in gravity tide is considered with re-calculated Love numbers. Frequency dependence of Love numbers for spherical harmonic tide upon the order number is discussed. Tidal displacement and tidally induced deviation of the vertical are also evaluated. Essential concepts underlying the body tide calculation are briefly summarized.
An Analysis of the Noise Influence on the Cross-well Travel-time Tomography to Detect a Small Scale Low Velocity Body
Lee, Doo-Sung ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 140~145
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.
A Study on the Static Correction for the First Arrival Travel-time of the Cross-well Seismic Data
Lee, Doo-Sung ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 146~151
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.
Applicability of the Small-Loop EM Method in the Sallow Marine Environment
Song, Sung-Ho ; Kim, Rae-Young ; Kang, Hye-Jin ; Cho, In-Ky ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 152~157
The small-loop electromagnetic (EM) method is one of the rapid and non-destructive geophysical methods and has been used widely for many geophysical investigations, particularly for shallow engineering and environmental surveys. Especially in the shallow marine environment, the small-loop EM technique is very effective because of rapid and convenient data acquisition, large signal and low noise level. However, the method has been rarely applied in the very conductive marine environment since it's penetration or investigation depth might be considered too low. In this study, we demonstrated that the small-loop EM method can be effectively applied in the extremely conductive marine environment through the analysis of 1D small-loop EM data. Furthermore, we confirmed that the resistivity distribution under the sea bottom can be quantitatively predicted from the 1D inversion results of synthetic and field data.
Investigation of Contamination Area from Landfill Using the Small-loop Electromagnetic Survey
Song, Sung-Ho ; Um, Jae-Yeon ; Cho, In-Ky ; Jung, Cha-Youn ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 158~163
The small-loop electromagnetic (EM) survey is an effective method to delineate contamination areas and pathways of contaminant plumes from landfill. A multi-frequency small-loop EM survey was applied to find them at landfill area, located in delta region, and checked the results with in-situ surveys including 24 trench excavations and 12 drilling boreholes. The correlation between these two results indicates this survey would be suitable to investigate the contamination area. However, it would be difficult to analyze low resistivity less than 10 ohm-m below 10 m depth in delta area without drilling survey because of a limitation to expand the penetration depth lower than 10 m depth due to the separation of 1.66 m between the two coils of GEM-2.
Modeling of Magnetotelluric Data Based on Finite Element Method: Calculation of Auxiliary Fields
Nam, Myung-Jin ; Han, Nu-Ree ; Kim, Hee-Joon ; Song, Yoon-Ho ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 164~175
Using natural electromagnetic (EM) fields at low frequencies, magnetotelluric (MT) surveys can investigate conductivity structures of the deep subsurface and thus are used to explore geothermal energy resources and investigate proper sites for not only geological
sequestration but also enhanced geothermal system (EGS). Moreover, marine MT data can be used for better interpretation of marine controlled-source EM data. In the interpretation of MT data, MT modeling schemes are important. This study improves a three dimensional (3D) MT modeling algorithm which uses edge finite elements. The algorithm computes magnetic fields by solving an integral form of Faraday's law of induction based on a finite difference (FD) strategy. However, the FD strategy limits the algorithm in computing vertical magnetic fields for a topographic model. The improved algorithm solves the differential form of Faraday's law of induction by making derivatives of electric fields, which are represented as a sum of basis functions multiplied by corresponding weightings. In numerical tests, vertical magnetic fields for topographic models using the improved algorithm overcome the limitation of the old algorithm. This study recomputes induction vectors and tippers for a 3D hill and valley model which were used for computation of the responses using the old algorithm.
Feasibility of Sparker Profiling for Investigation of the Rubble Mound Foundation in a Coastal Area
Kim, Han-Joon ; Jo, Churl-Hyun ; Na, Ji-Hoon ; Jou, Heong-Tae ; Shin, Sung-Ryul ;
Geophysics and Geophysical Exploration, volume 14, issue 2, 2011, Pages 176~178