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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 7, Issue 4 - Nov 2004
Volume 7, Issue 3 - Aug 2004
Volume 7, Issue 2 - May 2004
Volume 7, Issue 1 - Feb 2004
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Development and Application of a Seismic Tomography Software Based on Windows
Jung, Sang-Won ; Ha, Hee-Sang ; Ko, Kwang-Beom ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 157~163
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.
Application of SP Monitoring in the Pohang Geothermal Field
Lim Seong Keun ; Lee Tae Jong ; Song Yoonho ; Song Sung-Ho ; Yasukawa Kasumi ; Cho Byong Wook ; Song Young Soo ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 164~173
To delineate geothermal water movement at the Pohang geothermal development site, Self-Potential (SP) survey and monitoring were carried out during pumping tests. Before drilling, background SP data have been gathered to figure out overall potential distribution of the site. The pumping test was performed in two separate periods: 24 hours in December 2003 and 72 hours in March 2004. SP monitoring started several days before the pumping tests with a 128-channel automatic recording system. The background SP survey showed a clear positive anomaly at the northern part of the boreholes, which may be interpreted as an up-flow Bone of the deep geothermal water due to electrokinetic potential generated by hydrothermal circulation. The first and second SP monitoring during the pumping tests performed to figure out the fluid flow in the geothermal reservoir but it was not easy to see clear variations of SP due to pumping and pumping stop. Since the area is covered by some 360 m-thick tertiary sediments with very low electrical resistivity (less than 10 ohm-m), the electrokinetic potential due to deep groundwater flow resulted in being seriously attenuated on the surface. However, when we compared the variation of SP with that of groundwater level and temperature of pumping water, we could identify some areas responsible to the pumping. Dominant SP changes are observed in the south-west part of the boreholes during both the preliminary and long-term pumping periods, where 3-D magnetotelluric survey showed low-resistivity anomaly at the depth of
. Overall analysis suggests that there exist hydraulic connection through the southwestern part to the pumping well.
Empirical Rock Strength Logging in Boreholes Penetrating Sedimentary Formations
Chang, Chan-Dong ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 174~183
The knowledge of rock strength is important in assessing wellbore stability problems, effective sanding, and the estimation of in situ stress field. Numerous empirical equations that relate unconfined compressive strength of sedimentary rocks (sandstone, shale, and limestone, and dolomite) to physical properties (such as velocity, elastic modulus, and porosity) are collected and reviewed. These equations can be used to estimate rock strength from parameters measurable with geophysical well logs. Their ability to fit laboratory-measured strength and physical property data that were compiled from the literature is reviewed. While some equations work reasonably well (for example, some strength-porosity relationships for sandstone and shale), rock strength variations with individual physical property measurements scatter considerably, indicating that most of the empirical equations are not sufficiently generic to fit all the data published on rock strength and physical properties. This emphasizes the importance of local calibration before one utilizes any of the empirical relationships presented. Nonetheless, some reasonable correlations can be found between geophysical properties and rock strength that can be useful for applications related to wellhole stability where haying a lower bound estimate of in situ rock strength is especially useful.
Application of Electrical Resistivity Tomography to Analyze Soil Properties in Unsaturated Bone
Yong Hwan-Ho ; Song Sung-Ho ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 184~190
To analyze soil properties of unsaturated zone, we applied electrical resistivity tomography(ERT) of high resolution image. From linear relationship with each soil texture between results of ERT and soil properties such as electrical conductivity of pore water, water contents and ionic contents, we could be analyzed the result of ERT more effectively. Consequently, ERT can be useful for estimating soil properties between the two holes and evaluating indirectly pH and organic contents of soil.
Construction the pseudo-Hessian matrix in Gauss-Newton Method and Seismic Waveform Inversion
Ha, Tae-Young ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 191~196
Seismic waveform inversion can be solved by using the classical Gauss-Newton method, which needs to construct the huge Hessian by the directly computed Jacobian. The property of Hessian mainly depends upon a source and receiver aperture, a velocity model, an illumination Bone and a frequency content of source wavelet. In this paper, we try to invert the Marmousi seismic data by controlling the huge Hessian appearing in the Gauss-Newton method. Wemake the two kinds of he approximate Hessian. One is the banded Hessian and the other is the approximate Hessian with automatic gain function. One is that the 1st updated velocity model from the banded Hessian is nearly the same of the result from the full approximate Hessian. The other is that the stability using the automatic gain function is more improved than that without automatic gain control.
Electrical Resistivity Survey at the Ground with Micro-subsidence by Excessive Pumping of Groundwater
Song Sung-Ho ; Lee Kyu-Sang ; Yong Hwan-Ho ; Kim Jin-Ho ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 197~206
Because the minute displacement of ground accompanied by excessive pumping of groundwater at specified site is mainly generated from ill-balancing of water budget within groundwater basin, It is necessary to monitor the variation of micro-subsidence for a long time at representative points. We made up the conceptual model using two-dimensional electrical resistivity survey and three-dimensional soil profile consisted of loam and sand. In verifying the reliability of this conceptual model using numerical modeling for ground settlement and groundwater flowing, two-dimensional electrical resistivity survey with short distance of electrode following soil sampling with hand auger would be useful for interpreting hydrogeological structure related to the minute displacement of ground consisted of loam and sand.
Review on the Three-Dimensional Inversion of Magnetotelluric Date
Kim Hee Joon ; Nam Myung Jin ; Han Nuree ; Choi Jihyang ; Lee Tae Jong ; Song Yoonho ; Suh Jung Hee ;
Geophysics and Geophysical Exploration, volume 7, issue 3, 2004, Pages 207~212
This article reviews recent developments in three-dimensional (3-D) magntotelluric (MT) imaging. The inversion of MT data is fundamentally ill-posed, and therefore the resultant solution is non-unique. A regularizing scheme must be involved to reduce the non-uniqueness while retaining certain a priori information in the solution. The standard approach to nonlinear inversion in geophysis has been the Gauss-Newton method, which solves a sequence of linearized inverse problems. When running to convergence, the algorithm minimizes an objective function over the space of models and in the sense produces an optimal solution of the inverse problem. The general usefulness of iterative, linearized inversion algorithms, however is greatly limited in 3-D MT applications by the requirement of computing the Jacobian(partial derivative, sensitivity) matrix of the forward problem. The difficulty may be relaxed using conjugate gradients(CG) methods. A linear CG technique is used to solve each step of Gauss-Newton iterations incompletely, while the method of nonlinear CG is applied directly to the minimization of the objective function. These CG techniques replace computation of jacobian matrix and solution of a large linear system with computations equivalent to only three forward problems per inversion iteration. Consequently, the algorithms are efficient in computational speed and memory requirement, making 3-D inversion feasible.