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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Geophysics and Geophysical Exploration
Journal Basic Information
Journal DOI :
Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 12, Issue 4 - Nov 2009
Volume 12, Issue 3 - Aug 2009
Volume 12, Issue 2 - May 2009
Volume 12, Issue 1 - Feb 2009
Selecting the target year
P-wave Velocity Analysis Around the BSR Using Wide-angle Ocean-bottom Seismic Data
Kim, Byoung-Yeop ; Byun, Joong-Moo ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 173~182
In April 2008, KIGAM carried out an ocean-bottom seismometer (OBS) survey in the central Ulleung Basin where strong bottom simulating reflectors (BSRs) were revealed from previous surveys and some gas-hydrate samples were retrieved by direct sampling. The purpose of this survey is to estimate the velocity structure near the BSR in the gas hydrate prospect area using wide-angle seismic data recorded on the ocean-bottom seismometers. Along with the OBS survey, a 2-D seismic survey was performed whereby stratigraphic and preliminary velocity information was obtained. Two methods were applied to wide-angle data for estimating P wave velocity; one is velocity analysis in the
-p domain and the other is seismic traveltime inversion. A 1-D interval velocity profile was obtained by the first method, which was refined to layered velocity structure by the latter method. A layer stripping method was adopted for modeling and inversion. All velocity profiles at each OBS site clearly show velocity reversal at BSR depths due to the presence of gas hydrates. In addition, we could confirm high velocity in the column/chimney structure.
Application of Convolutional Perfectly Matched Layer Method to Numerical Elastic Modeling Using Rotated Staggered Grid
Cho, Chang-Soo ; Lee, Hee-Il ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 183~191
Finite difference method using not general SSG (standard staggered grid) but RSG (rotated staggered grid) was applied to simulation of elastic wave propagation. Special free surface boundary condition such as imaging method is needed in finite difference method using SSG in elastic wave propagation. But free surface boundary condition in finite difference method using RSG is easily solved with adding air layer or vacuum layer. Recently PML (Perfectly Matched layer) is widely used to eliminate artificial reflection waves from finite boundary because of its' greate efficiency. Absorbing ability of CPML (convolutional Perfectly Matched Layer) that is more efficient than that of PML and CPML that don't use splitting of wave equation that should be adapted to PML was applied to FDM using RSG in this study. Frequency absorbing characteristic and energy absorbing ability in CPML layer were investigated and CPML eliminated artificial boundary waves very effectively in FDM using RSG in being compared with that of Cerjan's absorbing method. CPML method also diminished amplitude of waves in boundary layer of solid-liquid model very well.
Processing of Side Scan Sonar and SBP Data for the Artificial Reef Area
Shin, Sung-Ryul ; Lim, Min-Hyuk ; Jang, Won-Il ; Lim, Jong-Se ; Yoon, Ji-Ho ; Lee, Seong-Min ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 192~198
Side scan sonar and SBP (sub-bottom profiler) play a very important role in the survey for seafloor imaging and sub-bottom profiling. In this study, we have acquired side scan sonar and SBP data from the artificial reef area. We applied digital image processing techniques to side scan sonar data in order to improve an image quality. For the enhancement of data quality and image resolution, we applied the typical seismic data processing sequence including gain recovery, muting, spectrum analysis, predictive deconvolution, migration to SBP data. We could easily estimate if artificial reef structures were settled properly and their distribution on the seafloor from the integrated interpretation of side scan sonar and SBP data. From the sampling analysis of seabed sediments, texture filtering of side scan sonar data and SBP data interpretation, we could evaluate the sediment type, distribution and thickness of seafloor sediments in detail.
Seismic Analysis of the Korean Peninsula Using Multiple Lapse Time Window Method
Chung, Tae-Woong ; Yoon, Suk-Yung ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 199~207
From 329 earthquake data in the Korean Peninsula, we separated the intrinsic and scattering quality factor (
) using the Multiple Lapse Time Window Analysis (MLTW) method. For the homogeneous velocity structure,
reduces the amplitudes of both direct and coda waves;
diminishes the direct wave amplitude but enlarges the coda wave amplitude. Based on this phenomenon, MLTW method analytically derives theoretical curves and obtains
by least square fit with observation curves. This study is the first approach for the seismic stable region by MLTW method, and show that
in the Korean Peninsula are very low at lower than frequencies of 5 Hz. This low value seems to be related to the inactive tectonism of the Korean Peninsula.
Derivation of Relation between Variation of Gradients of Antenna Tower of GNSS Permanent Observatories Depending on Diurnal Variation of External Air Temperature and Movement of Phase Center of Antenna
Lim, Mu-Taek ; Kwak, Byung-Wook ; Park, Yeong-Sue ; Rim, Hyoung-Rae ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 208~214
Using the GNSS data and tilt-meter data of Boeun (BOEN) and Goesan (GSAN) GNSS stations, we have calculated the differential distance vector variation with the calculation time span set to 1 hour and 3 hour and differential tilt vector variation along time and derived an indicator of similarity between the two variations along time. The similarity such calculated is rather lower than high. But as the existence of a circular type movement of the antenna's phase center's location due to the tilt's variation of the antenna tower because of the sunlight's diurnal change is certain, we recommend to take such diurnal variation of antenna's location into consideration when the correction error in DGNSS or the measured data at reference stations in VRS (Virtual Reference System) is broadcast.
Mortar Characterization using Electrical Resistivity Method
Farooq, Muhammad ; Park, Sam-Gyu ; Song, Young-Soo ; Kim, Jung-Ho ;
Geophysics and Geophysical Exploration, volume 12, issue 2, 2009, Pages 215~220
Cement based mortars are widely used to improve the soft ground of a dam site, highway construction, and karst voids. The mechanical properties of the mortar are well documented in literature, however very limited work is done on their physical properties such as electrical resistivity which is considered as one of the most important physical property known while improving the soft grounds. In this paper, electrical resistivity of the Portland cement mortars is examined by employing the Wenner technique. Cylindrical specimens with various water/cement ratios (w/c) ranges from 0.35, 0.45, 0.50 and 0.65 were cast and tested. The test results showed that the electrical resistivity of the mortar increases with increasing curing time and decreases with increasing water content and w/c. A reasonable, good relation was found between electrical resistivity and compressive strength of mortar.