• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.125-130
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• 2008

Electrical resistivity and seismic refraction surveys were conducted to investigate geologic structures and geotechnical characteristics of the subsurface in Dok-do island, along with rock physical properties. The resistivity results in Seo-do island show that the fault adjacent to the fisherman's shelter is a normal fault and extended towards the NW direction. Bedded Rapilli Tuff in the downstream was more severely influenced in depth by weathering and erosion than Trachy Andesite II in the upstream area. The physical properties of the rocks illustrate that Trachyte and Trachy Andesite are hardest, Massive Tuff Breccia is next, and Tuffs are the most soft rocks in Dok-do island.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.314-321
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• 2007

Recently, multi-dimensional joint inversion of geophysical data based on fundamentally different physical properties is being actively studied. Joint inversion can provide a way to obtaining much more accurate image of the subsurface structure. Through the joint inversion, furthermore, it is possible to directly estimate non-geophysical material properties from geophysical measurements. In this study, we developed a new algorithm for jointly inverting dc resistivity and seismic traveltime data based on the multiple constraints: (1) structural similarity based on cross-gradient, (2) correlation between two different material properties, and (3) a priori information on the material property distribution. Through the numerical experiments of surface dc resistivity and seismic refraction surveys, the performance of the proposed algorithm was demonstrated and the effects of different regularizations were analyzed. In particular, we showed that the hidden layer problem in the seismic refraction method due to an inter-bedded low velocity layer can be solved by the joint inversion when appropriate constraints are applied.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.178-184
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• 2002

For economy and convenience, seismic refraction survey is widely used in surveying for large civil engineering work. The purpose of this study is to obtain the numerical responses of various models using Kirchhoff migration, and to analyze its application to the real data processing. Synthetic traveltime curve was calculated by vidale's algorithm, and various models such as 2 or 3 layer model and irregular topography model are tested to simulate the response of real structure. In order to compare the effect of initial velocity model, true velocity models, inversion results by tomography, smooth velocity models are used as an initial guess. The responses of model data show that the algorithm of this study is more sensitive to initial velocity model than the reflection survey, so choosing a suitable initial velocity model will be the most important thing in real data processing.

• The Journal of Engineering Geology
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• v.11 no.2
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• pp.163-174
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• 2001

For quantitative evaluation of geotechnical engineering properties such as rippability and diggability, clear interpretation on the subsUJiace velocity structures should be preceded by figuring out top soil, weathered and soft rock layers, shape of basement, fracture zones, geologic boundary and etC. from the seismic refraction data. It is very important to set up suitable field parameters, which are the configuration of profile and its length, spacings of geophones and sources and topographic conditions, for increasing field data Quality. Geophone spacing of 3 to 5m is reconunended in the land slope area of house land development site. In refraction tomography technique, the number of source points should be more than a Cluarter of available channel number of instrument and the subsurface structure interpretation can be decreased the artifact of inversion by topographic effect. Compared with core logging data, it is shown that the velocity range of the soil is less than 700m/s, weathered rock 700~1,200m/s, soft rock 1,200~1,800m/s on the velocity tomogram section. And the upper limit of P-wave velocity for rippability is estimated 1,200 to 1,800m/s in land slope area of gneiss.

• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.441-450
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• 2006

The on-land seismic survey in Korea was begun in mid-1960s. Kim et al.(1967) of Korea Geological Survey reported on the result of gravity and seismic reflection surveys conducted in the Pohang area for the period of 1963-64 to assess its possibility of oil entrapment. Hyun and Kim (1966) carried out a refraction survey on the tunnel wall. Since then, the KGS geophysicists had conducted seismic surveys on Kyungsang sedimentary basin as a main project for several years. In 1970s, on-land seismic surveys had been conducted for various purposes such as site investigation for the nuclear power plants and industrial complex, exploration for ground water, mineral resources and underground tunnel. The first reflection survey with CMP acquisition was attempted in 1978 by using a digital recording system. But most of on-land seismic surveys had employed the refraction method until 1980s. In 1990s, high resolution reflection and various borehole seismic surveys such as tomography, uphole, downhole, cross-hole methods have been attempted by universities and engineering companies. The applications of on-land seismic surveys have been enlarged for both academic and industrial purposes such as investigation of geologic structure of the fault and tidal flat area, construction of highway, railroad and dam, geothermal energy and mineral resource exploration, environmental assessment for waste disposal sites and archaeological investigations. In 2002, the first crustal seismic survey was carried out on the profile of 294km length across the whole peninsular. It is expected that the advanced technology and experience acquired through offshore seismic surveys, which have been conducted in continental shelf of Korea and foreign oil fields, will stimulate the more active on-land seismic explorations.

• 한국지구물리탐사학회:학술대회논문집
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• 2002.09a
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• pp.101-125
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• 2002

A lake seismic survey was carried out to investigate possible geohazards for construction of the underground LPG storage at Namyang Lake. The proposed survey site has a land-lake combined geography and furthermore water depth of the lake is shallow. Therefore, various seismic methods such as marine single channel high resolution seismic reflection survey, sonobuoy refraction survey, land refraction survey and land-lake combined refraction survey were applied. Total survey amounts are 34 line-km of high resolution lake seismic survey, 14 lines of sonobuoy refraction survey, 890 m of land refraction survey and 8 lines of land-lake combined refraction survey. During the reflection survey, there were severe water reverberations from the lake bottom obscured subsurface profiling. These strong multiple events appeared in most of the survey area except the northern and southern area near the embankment where seems to be accumulated mainly mud dominated depositions. The sonobuoy refraction profiles also showed the same Phenomena as those of reflection survey. Meanwhile the results of the land-lake combined refraction survey showed relatively better qualities. However, the land refraction survey did not so due to low velocity soil layer and electrical noise. Summarized results from the lake seismic survey are that acoustic basement with relatively flat pattern appeared 30m below water level and showed three types of bedrock such as fresh, moderately weathered and weathered type. According to the results of the combined refraction survey, a velocity distribution pattern of the lake bottom shows three types of seismic velocity zone such as >4.5 km/s, 4.5-4.0km/s and <4.0km/s. The major fault lineament in the area showed NW-SE trend which was different from the Landsat image interpretation. A drilling was confirmed estimated faults by seismic survey.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.615-621
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• 2007

Seismic refraction survey which is assumed to be effective for investigating of the amount of bed sediment was applied to two sites having different soil types. The ten lines of seismic surveys were carried out in the areas of the levee near the Wolchon Bridge, Yongin and the Damam levee, Yecheon. At the same time, two borehole data were obtained to be used in classifying geological formations on the inverted seismic sections. As the results of interpolating the depths of geological formations and the surface elevation values, it is possible to estimate the volume of the bed sediments at $24,000m^3\;and\;56,000m^3$ in Yongin and Yecheon, respectively.

• Geophysics and Geophysical Exploration
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• v.5 no.1
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• pp.6-17
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• 2002

Refraction tomography was developed to interpret subsurface velocity structure easily in topographic conditions. It was applied to synthetic refraction data to find the factors for optimization of applicability of refraction tomography such as configuration of profiling and its length, spacing of geophones and sources and topographic conditions. Also, low velocity layer near VSP hole could be detected by joint inversion with refraction and VSP data. Continuity of subsurface velocity structure in two different spread lines for area of house land development was good in case of applying our algorithm and velocity structure was classified quantitatively to evaluate rippability for engineering works.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.43-48
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• 2017

The applicability of refraction survey has been tested using a wave glider widely used in long-term ocean observations around the world. To record seismic refractions, a single channel streamer with metal weight and a seismic recording system were mounted on the wave glider. We used GPS precise time synchronization signal and radio frequency (RF) communication to synchronize shot and recorder triggers and to control acquired data quality in real time. When the wave glider is positioned close to the set point, a 2,000 J sparker is exploded along the designed track at 2 second intervals. Through the test survey, we were able to successfully acquire refractions from the subsurface.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.95-100
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• 2006

To reveal subsurface structures of the Ulsan fault, seismic data were recorded along a 750-m long line near Nongso-Eup in Ulsan. P and S waves were generated simultaneously by impacting a 5 kg sledgehammer on a tilted plate. The data were received by 16 10-Hz 3-component geophones at 3 m intervals. Refracted P waves were inverted using the tomography method. Dip moveout and migration were applied to reflection data processed following a general sequence. Four layers were identified based on P-wave velocities and P- and S-wave stacked image. From top to bottom, the P-wave velocity of each layer ranges in $300{\sim}1100\;m/s$, $1100{\sim}1700\;m/s$, $1700{\sim}2700\;m/s$, and greater than 2700 m/s. The corresponding thickness of the top three layers averages 3.9 m, 5.9 m, 4.4 m, respectively. The S-wave stack section is effective to define subsurface structures shallower than 10 m.