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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 19, Issue 3 - Aug 2016
Volume 19, Issue 2 - May 2016
Volume 19, Issue 1 - Feb 2016
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An Electrical Resistivity Survey for Leachate Investigation at a Solid Waste Landfill
Lee, Keun-Soo ; Cho, In-Ky ; Mok, Jong-Koo ; Kim, Jeong-Woo ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 59~66
DOI : 10.7582/GGE.2016.19.2.059
The electrical resistivity method is an effective geophysical tool to detect subsurface contamination because the contaminated zones show generally lower electrical resistivity. In this study, the electrical resistivity surveys were applied to a waste landfill site to image the subsurface structure around the landfill and to identify the contaminated zones. First, the dipole-dipole 2D resistivity surveys were conducted along the boundaries of landfill to define the developed contaminated zones. Then the crosshole resistivity tomography was applied to confirm the suspected contaminated zones at depth. The results of drilling and geochemical analysis of ground water supported that the low resistivity zones coincide well with the contaminated zones and the leachate pathways could be delineated effectively from the resistivity survey.
Characteristics of Low-frequency Ambient Seismic Noise in South Korea
Park, Iseul ; Kim, Ki Young ; Byu, Joongmoo ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 67~75
DOI : 10.7582/GGE.2016.19.2.067
To investigate spatial and temporal variations of low-frequency (
) ambient seismic noise, we analyzed the noise data recorded for one whole year of 2014 at surface accelerometer stations in South Korea. After decomposed into low-frequency (LF; < 1 Hz) and high-frequency (HF;
) components, the root-mean-squared (RMS) amplitudes and power spectral densities (PSD) of the noise data were computed. The RMS amplitudes were larger on islands and near-shore stations, but also large RMS amplitudes were observed at inland stations in large cities only for HF components. The RMS amplitudes of HF components were larger in the daytime than at nighttime and during weekdays than on Sunday and holidays. This indicates the HF components are closely related to human activities. On the contrary, daily and weekly variations were not clear in the LF components while they showed seasonal variations with its maximum during the winter and a good correlation with significant wave height. Therefore, we interpret the mechanism of LF components is closely related to natural phenomena such as sea. The amplitude of LF components decreased as an exponential function of the distance to the center of typhoons. The exponential index of -0.76 suggested that ambient seismic noise included both surface and body waves. Peak frequencies of the PSD curves were near 0.34 Hz indicating the double frequency. No temporal variation in the peak frequency was clearly noticed.
Improvement of Reverse-time Migration using Homogenization of Acoustic Impedance
Lee, Gang Hoon ; Pyun, Sukjoon ; Park, Yunhui ; Cheong, Snons ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 76~83
DOI : 10.7582/GGE.2016.19.2.076
Migration image can be distorted due to reflected waves in the source and receiver wavefields when discontinuities of input velocity model exist in seismic imaging. To remove reflected waves coming from layer interfaces, it is a common practice to smooth the velocity model for migration. If the velocity model is smoothed, however, the subsurface image can be distorted because the velocity changes around interfaces. In this paper, we attempt to minimize the distortion by reducing reflection energy in the source and receiver wavefields through acoustic impedance homogenization. To make acoustic impedance constant, we define fake density model and use it for migration. When the acoustic impedance is constant over all layers, the reflection coefficient at normal incidence becomes zero and the minimized reflection energy results in the improvement of migration result. To verify our algorithm, we implement the reverse-time migration using cell-based finite-difference method. Through numerical examples, we can note that the migration image is improved at the layer interfaces with high velocity contrast, and it shows the marked improvement particularly in the shallow part.
Derivation the Correction of the Component of the Recorder and the Application of Hilbert Transformation to Calculating the Frequency Response of the Sensor
Cho, Chang Soo ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 84~90
DOI : 10.7582/GGE.2016.19.2.084
The validation of performance test for newly developed or old-used sensor is very important in the earthquake monitoring and seismology using earthquake data. Especially the frequency response of the sensor is mainly used to correct the earthquake data. The technique of the calculation of phase and amplitude with Hilbert transformation for earthquake data that is filtered with band limited frequency in time domain is applied to calculate the frequency response of the sensor. This technique was tested for the acceleration sensors, CMG-5T of 1g and 2g installed on the vibration table at the laboratory and we could obtain satisfactory result. Tohoku large earthquake in 2011 observed at the station SNU that has accelerometer, ES-T and seismometer, STS-2 operated by KIGAM was also used to test the field data applicability. We could successfully get the low frequency response of broad band sensor, STS-2. The technique by using band limited frequency filter and Hilbert transformation showed the superior frequency response to the frequency spectrum ratio method for noisy part in data.
A Least Square Fit Analysis on the Earth's Polar Motion Time Series: Implication against Smylie's Conjecture
Chung, Tae-Woong ; Na, Sung-Ho ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 91~96
DOI : 10.7582/GGE.2016.19.2.091
From the Earth's polar motion time series (IERS 08 C04, since 1981), after removal of seasonal variation by band-pass filtering, we acquired Earth's free Eulerian motion (Chandler wobble) time series. By successive least square error fittings on it, we analyzed amplitude and phase variation of Chandler wobble. We attempted to identify any precursory behavior of the pole before large earthquakes but only to fail. Unlike Smylie's conjecture there was no appreciable motion of the Earth's pole detected at around the each times of recent six largest earthquakes of magnitude over 8.5.
Location of Recent Micro-earthquakes in the Gyeongju Area
Han, Minhui ; Kim, Kwang-Hee ; Son, Moon ; Kang, Su Young ; Park, Jung-Ho ;
Geophysics and Geophysical Exploration, volume 19, issue 2, 2016, Pages 97~104
DOI : 10.7582/GGE.2016.19.2.097
Small to large earthquakes have been reported in Gyeongju and its vicinity in southeast Korea during historical period as well as instrumental observation period. We identified and located more than 300 earthquakes that occurred between January 2010 and December 2014 in a
area, but were unreported because of their small magnitudes. We used the Joint Hypocenter Determination (JHD) method to minimize the influence of the differences between the actual earth structure and 1-D velocity model for earthquake locations. The potential relationship between the previously reported Quaternary faults and the earthquake hypocenters was investigated. Many micro-earthquakes were found to be located in the southern segment of the Yeonil Tectonic Line, the Seokup fault, and the Waup basin boundary faults.