• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.17-24
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• 1999

The porvision against earthquakes and aseismic design of nuclear power plants (NPPs) in Korea are composed of four stages: site-selection, design, construction, and operation stages, Since regulatory criteria are strictly applied in each stage, the NPPs in Korea are believed to have a sufficient safety against maximum potential earthquakes. However, it has been recognized that those regulatory criteria borrowed from U.S. should be replace by Korea-specific ones by using earthquake data obtained from earthquake observation at and around NPP sites. Also, the government made a plan after the Yongwol and th Kyongju earthquakes that the regulatory body operates an independent earthquake network in order to reinforce the earthquake preparedness of NPPs. In compliance with the government's plan, this project is aiming at deployment of an earthquake motoring network composed of four seismic stations at NPP sites to record earthquake ground motions at NPP sites, to derive attenuation formulas of various ground motions and site-specific response spectra, and to develop structural intergrity assesment program.

• Earthquakes and Structures
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• v.13 no.1
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• pp.17-27
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• 2017

In this study, the characteristics of site amplification at seismic observation stations in Japan were estimated using the attenuation relationship of each station's response spectrum. Ground motion records observed after 32 earthquakes were employed to construct the attenuation relationship. The station correction factor at each KiK-net station was compared to the transfer functions between the base rock and the surface. For each station, the plot of the station correction factor versus the period was similar in shape to the graphs of the transfer function (amplitude ratio versus period). Therefore, the station correction factors are effective for evaluating site amplifications considering the period of ground shaking. In addition, the station correction factors were evaluated with respect to the average shear wave velocities using a geographic information system (GIS) dataset. Lastly, the site amplifications for specific periods were estimated throughout Japan.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.45-49
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• 2003

The velocity structure beneath the CHNB broadband station is determined by receiver function analysis using by from teleseismic P waveforms. The detailed broadband receiver functions are obtained by stacking method for source-equalized vertical, radial and tangential components of teleseismic P waveforms. A time domain inversion uses the stacked radial receiver function to determine vertical P wave velocity structure beneath the station. The crustal velocity structures beneath the stations are estimated using the receiver function inversion method in the case at the crustal model parameterized by many thin, flat-tying, homogeneous layers. The result of crust at model inversion shows the crustal velocity structure beneath the CHNB station varies smoothly with increasing depth, and there are six discontinuity around 2.5km, 6.25km, 12.5km, 22.5km and 27.5km depth, with Moho discontinuity at about 32.5km depth.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.3-7
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• 2003

The velocity structure beneath the CHNB broadband station is determined by receiver function analysis using by from teleseismic P waveforms. The detailed broadband receiver functions are obtained by stacking method for source-equalized vertical, radial and tangential components of teleseismic P waveforms. A time domain inversion uses the stacked radial receiver function to determine vertical P wave velocity structure beneath the station. The crustal velocity structures beneath the stations are estimated using the receiver function inversion method in the case at the crustal model parameterized by many thin, flat-lying, homogeneous layers. Events divide into 4 groups. four azimuths corresponding to events in group a(southwest), b(south), c(southeast), d(northeast). The result of crust at model inversion shows the crustal velocity structure beneath the CHNB station varies smoothly with increasing depth. The conard discontinuity lies around 18 km and moho discontinuity lies range from 30 to 34 km.

• Geophysics and Geophysical Exploration
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• v.11 no.2
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• pp.137-147
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• 2008

Fault rupture directivity of the Odaesan earthquake, which was inferred to be the main cause of the high PGAvalue (> 0.1 g) unusually observed at the near-source region, was analyzed by using the data from the nearby (R < 100 km) dense seismic stations. The Boatwright's method (2007) was adopted for this purpose in which the azimuth and takeoff angle of the unilateral rupture directivity function could be estimated based on the relative peak ground-motions of seismic stations resulting from the nature of the rupture directivity. In this study, the approximate values of the relative peak ground-motions was derived from the difference between the log residuals of the point-source spectral model (Boore, 2003) for the main and secondary events based on the Random Vibration Theory. In this derivation, the spectral difference for a frequency range between the source corner frequencies of main and secondary events was considered to reflect only the effect of the fault directivity. The inversion result of the model parameters for the fault directivity function showed that the fault-plane of NWW-SEE direction dipping steeply to the North with high rupture velocity near upward in SE direction is responsible for the observed high level of ground-motion at the near-source region.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.286-294
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• 2010

Korea Institute of Geoscience and Mineral Resources (KIGAM) has installed and operated seven seismoacoustic (infrasound) arrays as well as seismic stations in Korea. The seismo-acoustic array, which consists of co-located seismometers and micro-barometers, can observe both seismic and infrasonic signals from distant explosive phenomena. The infrasound is defined as low frequency (<20 Hz) acoustic waves in atmosphere. In particular, it can be detectable at long distance due to its low energy attenuation during propagation in atmosphere. KIGAM adopted the infrasound technology to discriminate surface explosions from earthquakes only because the surface explosion generally generates infrasound following seismic signal. In addition to surface explosions, these arrays have detected diverse geophysically natural and artificial phenomena, such as infrasound signal from the North Korean nuclear test. This review introduced the state-of-the-art studies and examples of infrasonic signals in and around the Korean Peninsula. In conclusion, infrasound technology would be clearly accepted itself as a new Earth monitoring technology by expanding its detectable regime to lithosphere-Earth surface-atmosphere. In future, an advanced technology, which allows to analyze seismic and infrasonic wave fields together, will enlarge the understanding of geophysical phenomena and be used as a robust analysis method for remote explosive phenomena in the broad infrasound regime.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.125-130
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• 2006

Both surface seismic and far-offset VSP data were recorded alongtwo mutually perpendicular profiles in the Pungam basin. The first-arrival times were simultaneously inverted using the tomography method. For the surface data, seismic energy was generated by a 5-kg sledgehammer at 48 stations and detected by 21 surface geophones at 3 m intervals and one 3-component geophone in test borehole for the purpose of static corrections. For the VSP data, seismic waves generated by the sledgehammer on the ground were detected by a 3-component borehole geophone in a depth range of $9{\sim}99\;m$. Delay times of the hammer data were corrected using the seisgun data before the inversion to yield velocity tomograms. The tomograms indicates that the soil layer with velocities less than 750 m/s averages 1.8 m thick. The velocity varies from 5353 m/s at the depth range of $31{\sim}40\;m$ to 4262 m/s at the depth range of $65{\sim}73\;m$. Compared with core samples, the relatively large variation in velocity may due to lithology changes and fracture effects with depth.

• Tunnel and Underground Space
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• v.19 no.5
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• pp.432-439
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• 2009

For more reliable estimation of seismic source, attenuation properties and dynamic ground property, site amplification function should be considered. Among various estimation methods, this study used the Nakamura's method (1989) for estimating site amplification characteristics. This method was originally applied to the surface waves of background noise and therefore there are some limitations in applying to general wave energy. However, recently this method has been extended and applied to the S wave energy successfully. This study applied the method to S wave and Coda wave energy, which is equivalent to the backscattered S wave energy. We used more than 60 observed ground motions from 5 earthquakes which were occurred recently, with magnitude range from 3.6 to 5.1. Each station showed characteristic site amplification property in low-, high- and resonance frequencies. Some of the stations showed as high as 4 times of site amplification in the range of specific frequencies, which may imply abnormal small scale geologic strata below the station or development of various trapped modes in the basin structure. Moreover, removal of site amplification can give us more reliable seismic source and attenuation parameters, addition to the seismic hazard estimation.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.4
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• pp.405-414
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• 2001

Plate tectonics is a dominant paradigm in modern geophysics. Because of its geological mechanism, Korea has a possibility of earthquake according to plate motion. Besides the disaster of earthquake grows rapidly, the importance of recognition for earthquake has been emphasized. This study attempts to decide crustal movement parameters with GPS data, analysed baseline after processing data with GIPSY-OASIS II S/W, observed from 6 stations in and around the Korean peninsula, and obtained from selected 11 stations in Korea. As a results, maximum shear strain was $0.04{\mu}/yr$ and the mean azimuth of the maximum compression axes$(A_{z2})$ is estimated as $97.75^{\circ}$ in and around the Korean peninsula. The average rate of the maximum shear strain($({\gamma}_max)$) is $0.17{\mu}/yr$. The mean azimuth of the maximum compression axes$(A_{z2})$ is estimated as $70.25^{\circ}$ in Korea. Such a pattern of strain distribution is harmonious with that of seismic activity in Korea both historically as well as today.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.1
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• pp.47-54
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• 2015

In this study, we developed strategies for pre-processing GNSS data for the purpose of separating geodetic factors from crustal deformation due to the earthquakes. Before interpreting GNSS data analysis results, we removed false signals from GNSS coordinate time series. Because permanent GNSS stations are located on a large tectonic plate, GNSS position estimates should be affected by the tectonic velocity of the plate. Also, stations with surrounding trees have seasonal signals in their three-dimensional coordinate estimates. Thus, we have estimated the location of an Euler pole and angular velocities to deduce the plate tectonic velocity and verified with geological models. Also, annual amplitudes and initial phases were estimated to get rid of those false annual signals showing up in the time series. By considering the two effects, truly geodetic analysis was possible and the result was used as preliminary data for analyzing post-seismic deformation of the Korean peninsula due to the Tohoku-oki earthquake.