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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
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
Selecting the target year
Comparison of Backgroud Noise Characteristics between Surface and Borehole Station of Hwacheon
Yun, Won Young ; Park, Sun-Cheon ; Kim, Ki Young ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 203~210
DOI : 10.7582/GGE.2013.16.4.203
To look into site characteristics of the Hwacheon borehole seismic station, we analyzed property of earthquake and microtremor recorded on surface and borehole seismometers. Acoording to analysis result of microtremor, the surface-to-borehole energy ratio was approximately 15 times greater during the daytime than during the nighttime, and the surface-to-borehole ratios of spectral amplitudes as frequency increases. For earthquake data, amplitude spectra and dominant frequency were computed using surface and borehole data. As a result, small earthquakes with short distance recorded on surface seismometer peaked at 8 Hz, 46 Hz. This result corresponds to resonance frequencies (7.4 Hz, 46 Hz) calculated by H/V spectral ratio. We confirmed amplification effect by site characteristics of overburden. Background noise level was approximately 20,000 times smaller at borehole seismic station than surface seismic station. These results provide strong evidence for the superior recording of earthquakes using borehole seismometers instead of surface seismometers.
Application of Effective Regularization to Gradient-based Seismic Full Waveform Inversion using Selective Smoothing Coefficients
Park, Yunhui ; Pyun, Sukjoon ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 211~216
DOI : 10.7582/GGE.2013.16.4.211
In general, smoothing filters regularize functions by reducing differences between adjacent values. The smoothing filters, therefore, can regularize inverse solutions and produce more accurate subsurface structure when we apply it to full waveform inversion. If we apply a smoothing filter with a constant coefficient to subsurface image or velocity model, it will make layer interfaces and fault structures vague because it does not consider any information of geologic structures and variations of velocity. In this study, we develop a selective smoothing regularization technique, which adapts smoothing coefficients according to inversion iteration, to solve the weakness of smoothing regularization with a constant coefficient. First, we determine appropriate frequencies and analyze the corresponding wavenumber coverage. Then, we define effective maximum wavenumber as 99 percentile of wavenumber spectrum in order to choose smoothing coefficients which can effectively limit the wavenumber coverage. By adapting the chosen smoothing coefficients according to the iteration, we can implement multi-scale full waveform inversion while inverting multi-frequency components simultaneously. Through the successful inversion example on a salt model with high-contrast velocity structures, we can note that our method effectively regularizes the inverse solution. We also verify that our scheme is applicable to field data through the numerical example to the synthetic data containing random noise.
Time-lapse Inversion of 3D Resistivity Monitoring Data
Kim, Yeon-Jung ; Cho, In-Ky ; Yong, Hwan-Ho ; Song, Sung-Ho ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 217~224
DOI : 10.7582/GGE.2013.16.4.217
We developed a time-lapse inversion using new cross-model constraints based on change ratio and resolution of model parameters. The cross-model constraint based on change ratio imposes the same penalty on the model parameters with equal change ratio. This constraint can emphasize the model parameters with significant change regardless of their increase or decrease. The resolution cross-model constraint imposes a small penalty on the model parameters with poor resolution, but a large penalty on the model parameters with good resolution. Thus, the model parameter with poor resolution can be effectively identified in the inversion result if they are significantly changed with time. Through the numerical tests for 3D resistivity monitoring data sets, the performance of these two cross-model constraints was confirmed. Finally, for the safety estimation of a sea dyke, we applied the developed time-lapse inversion to the 3D resistivity monitoring data that were acquired at a sea dike located in western coastal area of Korea. The result of time-lapse inversion suggested that there were no significant changes at the sea dike during the monitoring period.
Automatic Velocity Analysis by using an High-resolution Bootstrapped Differential Semblance Method
Choi, Hyungwook ; Byun, Joongmoo ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 225~233
DOI : 10.7582/GGE.2013.16.4.225
The accuracy of the automatic NMO velocity analysis, which is used for an effective and objective NMO velocity analysis, is highly affected by the velocity resolution of the velocity spectrum. In this study, we have developed an automatic NMO velocity algorithm, where the velocity spectra are created using high-resolution bootstrapped differential semblance (BDS), and the velocity analysis on CMP gathers is performed in parallel with MPI. We also compared the velocity models from the developed automatic NMO velocity algorithm with high-resolution BDS to those from BDS. To verify the developed automatic velocity analysis module we created synthetic seismic data from a velocity model including horizon layers. We confirmed that the developed automatic velocity analysis module estimated velocity more accurately. In addition, NMO velocity which yielded a CMP stacked section, where the coherency of the events were improved, was estimated when the developed module was applied to a marine field data set.
Hydroacoustic Observation on the 2011 Tohoku Earthquake
Yun, Sukyoung ; Lee, Won Sang ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 234~239
DOI : 10.7582/GGE.2013.16.4.234
9.0 thrust-fault earthquake has occurred in the Pacific coast of Tohoku, Japan, on March 11, 2011. We present the detection of the great earthquake and analyze T-waves associated with the main event and two other big aftershocks (
> 7) recorded in a hydroacoustic array (H11N) in the Pacific Ocean by performing array and spectral analysis to examine characteristics of T-waves generated from the big events. The complex rupture process of the main event directly influences on the shape of the T-waves, and the peak locates on where T-waves excited from fast rupturing process arrive. We compare the two aftershocks with different fault type and show that the fault type and the source depth change shape and spectral contents of T-waves.
Swell Effect Correction for the High-resolution Marine Seismic Data
Lee, Ho-Young ; Koo, Nam-Hyung ; Kim, Wonsik ; Kim, Byoung-Yeop ; Cheong, Snons ; Kim, Young-Jun ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 240~249
DOI : 10.7582/GGE.2013.16.4.240
The seismic data quality of marine geological and engineering survey deteriorates because of the sea swell. We often conduct a marine survey when the swell height is about 1 ~ 2 m. The swell effect correction is required to enhance the horizontal continuity of seismic data and satisfy the resolution less than 1 m. We applied the swell correction to the 8 channel high-resolution airgun seismic data and 3.5 kHz subbottom profiler (SBP) data. The correct sea bottom detection is important for the swell correction. To detect the sea bottom, we used maximum amplitude of seismic signal around the expected sea bottom, and picked the first increasing point larger than threshold value related with the maximum amplitude. To find sea bottom easily in the case of the low quality data, we transformed the input data to envelope data or the cross-correlated data using the sea bottom wavelet. We averaged the picked sea bottom depths and calculated the correction values. The maximum correction of the airgun data was about 0.8 m and the maximum correction of two kinds of 3.5 kHz SBP data was 0.5 m and 2.0 m respectively. We enhanced the continuity of the subsurface layer and produced the high quality seismic section using the proper methods of swell correction.
Evaluating Shear Wave Velocity of Rock Specimen Through Compressional Wave Velocities Obtained from FFRC and Ultrasonic Velocity Methods
Bang, Eun Seok ; Park, Sam Gyu ; Kim, Dong Soo ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 250~256
DOI : 10.7582/GGE.2013.16.4.250
Using shear wave velocity is more reasonable to estimate strength and integrity of rock compared with using compressional wave. It is often ambiguous to pick the dominant frequency caused by torsional wave when evaluating
of rock specimen from FFRC method. It is also sometimes ambiguous to pick the first arrival point of S wave compared with P wave in the signals acquired from ultrasonic velocity method. Otherwise, the procedure of evaluating
using ultrasonic velocity method and
using FFRC method is relatively stable. Through the relationship between elastic modulus, poisson's ratio and
can be obtained from
. Applicability was checked using model specimens having different material property and length and rock specimens sampled in mine area, and usefulness of proposed procedure was verified.
A Study of 3D Ore-Modeling by Integrated Analysis of Borehole and Geophysical Data
Noh, Myounggun ; Oh, Seokhoon ; Ahn, Taegyu ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 257~267
DOI : 10.7582/GGE.2013.16.4.257
3-D ore modeling was performed to understand the configuration of ore bodies by integrated analysis of borehole and geophysical data in iron-mine area. Five representative indices of rocks were designated, which were obtained from geological survey and borehole. The five indices of rocks were geostatistically simulated by Sequential Indicator Simulation method to delineate boundary of the ore bodies. And Ordinary Kriging and Sequential Gaussian Simulation was applied to make secondary information using resistivity data from magnetotellurics and DC resistivity survey, and this information was used for simple kriging with local varying means, one of integrated kriging techniques. From the correlation analysis between each properties, it was found that high grade of ore is characterized by increased density, whereas the electrical resistivity decreases. With the integrated results of geophysical and borehole data, it was also found that the real configuration of ore body was similar to the modeled result and information about ore grade in 3-D space was obtained.
Volcano Monitoring Using Earthquakes
Han, Arim ; Park, Iseul ; Kim, Ki Young ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 268~274
DOI : 10.7582/GGE.2013.16.4.268
Continuous seismic observation of volcanic earthquakes related to migration of magma or gas, is one of the most important methods used to monitor active volcanoes. In this review paper, we introduce the characteristics of volcanic earthquakes and their classification based on locations of foci, waveforms, frequencies, lithology, and source mechanisms. We also present some examples of successful warnings of volcanic eruptions and the present status of some observations of volcanic earthquakes in Japan, the United States, Italy, and New Zealand.
Suggestion for the Maintenance Program of the Sea Dike Using Geophysical Methods
Yong, Hwan-Ho ; Cho, In-Ky ; Song, Sung-Ho ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 275~283
DOI : 10.7582/GGE.2013.16.4.275
The sea dike is the most important facility of reclamation projects, and plays an important role in securing freshwater in the reservoir. Systematic research on practical approaches and data analysis techniques are lacking even though some geophysical methods such as electrical resistivity and self-potential surveys are included within the inspection processes. Hence, geophysical methods were considered for improvement of precision safety diagnosis methods after problems in the maintenance system have been identified, such as safety checks and precision safety diagnoses. In addition, geophysical methods customized according to variations in ambient environmental limiting factors such as pore pressure changes by tidal fluctuation, compaction characteristics of the fill materials, and the surface condition of the embankment were suggested.
Reliability of Strain Estimation on Triangular Network and A Case Study; Deformation of Korea due to 2011 Tohoku Earthquake observed by GPS
Na, Sung-Ho ; Chung, Tae Woong ; Choi, Byung-Kyu ; Yoo, Sung-Moon ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 284~292
DOI : 10.7582/GGE.2013.16.4.284
A stable procedure is presented to attain most probable and unbiased estimate of principal strain, rotation, and dilatation for 2-dimensional geodetic data on triangular network. The proper network size should be chosen carefully, because the errors of these estimates of strain tensor and other associated observables grow inversely proportional to the area of station triangle. As a case study, the deformation observables for the GPS-monitored co-seismic displacement in Korea due to the 2011 Tohoku-Oki earthquake were attained accordingly.
Multiple Lapse Time Window Analysis of the Korean Peninsula Considering Focal Depth
Chung, Tae Woong ; Rachman, Asep Nur ;
Geophysics and Geophysical Exploration, volume 16, issue 4, 2013, Pages 293~299
DOI : 10.7582/GGE.2013.16.4.293
The recent Multiple Lapse Time Window (MLTW) analysis of Korean Peninsula event showed that the focal depth was far greater influence factor than the velocity structure of the model, applying the analysis of the direct simulation Monte Carlo (DSMC) method. Thus, using the events with focal depth of about 10 km, this study considered 330 paths connecting 41 events and 71 stations, and re-examined uniform and depth-dependent velocity models previously studied. As a result, the residual of misfit function greatly decrease from analytic model to DSMC model, reflecting variation of the focal depth from 0 to 10 km. On the other hand, the difference of residuals for each velocity model were relatively small.