• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.33-40
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• 2009

In field surveys using the dipole-dipole electrical resistivity method, we often encounter negative apparent resistivity. The term 'negative apparent resistivity' refers to apparent resistivity values with the opposite sign to surrounding data in a pseudosection. Because these negative apparent resistivity values have been regarded as measurement errors, we have discarded the negative apparent resistivity data. Some people have even used negative apparent resistivity data in an inversion process, by taking absolute values of the data. Our field experiments lead us to believe that the main cause for negative apparent resistivity is neither measurement errors nor the influence of self potentials. Furthermore, we also believe that it is not caused by the effects of induced polarization. One possible cause for negative apparent resistivity is the subsurface geological structure. In this study, we provide some numerical examples showing that negative apparent resistivity can arise from geological structures. In numerical examples, we simulate field data using a 3D numerical modelling algorithm, and then extract 2D sections. Our numerical experiments demonstrate that the negative apparent resistivity can be caused by geological structures modelled by U-shaped and crescent-shaped conductive models. Negative apparent resistivity usually occurs when potentials increase with distance from the current electrodes. By plotting the voltage-electrode position curves, we could confirm that when the voltage curves intersect each other, negative apparent resistivity appears. These numerical examples suggest that when we observe negative apparent resistivity in field surveys, we should consider the possibility that the negative apparent resistivity has been caused by geological structure.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.197-202
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• 2005

The electromagnetic signals associated with the seismic activity in the south-east offshore of Kii peninsula, Japan, were clearly recorded at the MT sites in Jeju island, Korea. In this research, we have identified the co-seismic electromagnetic signals associated with the seismic activity and have analyzed the characteristics of significant electromagnetic variations. The analysis of phase velocity, power spectral density, MT impedance and polarization direction shows that the significant earthquake signals have the frequency band of about 0.05 to 0.5 Hz and that the sources of electromagnetic field are local effects of passing seismic waves. The simple approximation using electrokinetic effect successfully explains the co-seismic EM signals coincides with measured data but cannot explain the localities of electromagnetic variations.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.654-664
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• 2011

A field campaign of magnetotelluric (MT) and audio-frequency MT (AMT) survey was done at 36 measurement points as a complementary for the previous 44 MT measurements completed during the period of 2005-2006. The purpose of additional MT survey is to investigate the possible fracture system in Seokmo Island, which is conceived to be crucial in accumulation and migration of geothermal hot spring in this area. We have done 2D and 3D inversions of overall MT and AMT data distributed on a grid to interpret subsurface of extended area. The inversion results reveal that at least two major faults are imaged in the inversion results, one of which is in NNE-SWW with steep dip, and another is in E-W direction.

• 한국지구물리탐사학회:학술대회논문집
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• 2001.09a
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• pp.75-89
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• 2001

There are 334 coal mines and about 900 metal mines abandoned. The environmental problems such as acid mine drainage from adits etc. and the subsidence has occurred in the abandoned mines. In addition, soil has been contaminated by tailings. According to analysis of mine drainages, some of them from adits in the abandoned coal and metallic mines were acidic and polluted by heavy metals. Especially, water quality of coal mine drainages were different by areas. Treatment of mine drainage by conventional chemical treatment has the drawback because the operating cost is very expensive. The treatment system used in mine drainage is the natural treatment system such as anoxic limestone drain in adits and the constructed wetland. The method of reclamation for abandoned waste rocks and tailings impoundments are mainly landfilling.

• The Journal of the Acoustical Society of Korea
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• v.26 no.1E
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• pp.33-38
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• 2007

Compressional wave velocity and shear wave velocity were measured for gassy sediments collected from Jinhae Bay, Korea. To distinguish inhomogeneities of gassy sediments, Computed Tomography (CT) was carried out for gassy sediment using CT Scanner. The cored sediments are composed of homogeneous and soft mud (greater than $8{\Phi}$ in mean grain size) containing clay content more than 50%. In depth interval of gassy sediments, compressional wave velocity is significantly decreased from 1480m/s to 1360m/s, indicating that the gas greatly affects compressional wave velocity due to a gas and/or degassing cracks. Shear wave velocity shows a slight increasing pattern from ${\sim}55\;m/s$ in the upper part of the core to ${\sim}58\;m/s$ at 320 cm depth, and then decreases to ${\sim}54\;m/s$ in the lower part of the core containing a small amount of gas. But shear wave velocity in the gassy sediments is slightly greater than that of non-gassy sediments in the upper part of the core. Thus, the Vp/Vs ratio is decreased (from 30 to 25) in gas charged zone. The Vp/Vs ratio is well correlated with shear wave velocity, but no correlation with compressional wave velocity. This suggests that low concentrations of gas have little affects on shear wave velocity. By CT images, the gas in the sediments is mostly concentrated around inner edge of core liner due to a long duration after sediment collection.

• Korean Journal of Remote Sensing
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• v.20 no.6
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• pp.369-382
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• 2004

The purpose of this study is the investigation of applicability of LSMA(Linear Spectral Mixture Analysis) on the geological uses with different radiometric and spatial types of sensor images such as Terra ASTER and LANDSAT 7 ETM+. As for the actual application case, geologic mapping for mineral exploration using ASTER and ETM+ at the Mongolian plateau region was carried out. After the pre-processing such as the geometric corrections and calibration of radiance, 7 endmembers, as spectral classes for geologic rock types, related to spectral signature deviation for the given application was determined by the pre-surveyed geological mapping information and the correlation matrix analysis, and total 20 images of ASTER and ETM+ were used to LSMA processing. As the results, fraction maps showing individual mineral types in the study area are presented. It concluded that this approach based on LSMA using ETM+ and ASTER is regarded as one of the effective schemes for geologic remote sensing.

• Journal of the Korean Geophysical Society
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• v.7 no.2
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• pp.113-120
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• 2004

Hydrochemical characteristics of deep groundwater at Surak-ri, Nonsan-gun, Chungnam Province was explained by major ion concentration, water type, and phase stability diagram. The area is composed of meta-sedimentary rock and quartz pophyry. The 5 boreholes where deep groundwater was sampled and analyzed are located on the meta-sedimentary rocks and drilling depth range of the wells is from 554 m to 928 m. pH, TDS, Na, and SiO2 values are high in the groundwater from meta-sedimentary area intruded by quartz pophyry, while Ca is high in the groundwater from meta-sedimentary area. K and Mg concentrations are low but F concentration is high both groundwater. The content of major anions is in the order of CO3(HCO3)>Cl>SO4(F) in both geology, while that of major cations shows the order of Na>Ca>K(Mg) in meta-sedimentary area intruded by quartz porphyry and a>Na>Mg>Na in meta-sedimentary area. Based on the phase equilibrium in the systems Na2O-Al2O3-SiO2-H2O and K2O-Al2O3-SiO2-H2O, the groundwater is saturated with respect to Quartz and more evolved compared with the natural mineral water. It is concluded that chemical evolution in the groundwater from meta-sedimentary area intruded by quartz porphyry, is nearly saturated with respect to feldspar, while the groundwater from meta-sedimentary area continue to proceed with increasing pH by reaction of feldspar.

• Journal of Soil and Groundwater Environment
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• v.23 no.2
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• pp.1-14
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• 2018

The recent increase in demand for lithium has led to the development of new brine prospects, The brines are hosted in closed salar basin aquifers of two types that are mature halite salars and immature clastic salars. Salar brines also contain other elements of commercial interest, most notably potassium and boron. As a result, there has been a plethora of new exploration projects focused on the brines hosted in the aquifers of the intermontane-closed basins. The estimate of lithium resources and reserves in these salars depends on a detailed knowledge of aquifer geometry, porosity, and brine grade. Because the resource is in a fluid state, it has the propensity to move, mix, rearrange itself relatively rapidly during the course of a project lifetime, and lower recovery factors compared with most metalliferous and industrial mineral deposits due to reliance on pumping of the brine from wells for extraction. This is unlike any other type of metallic mineral resource and hence a different approach specially focusing on hydrogeology and brine hydrology is required for these prospects.

• Geomechanics and Engineering
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• v.37 no.6
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• pp.577-590
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• 2024

With increasing demand for nuclear power generation, nuclear structures are being planned and constructed worldwide. A grave safety concern is that these structures are sensitive to large-magnitude shaking, e.g., during earthquakes. Seismic response analysis, which requires P- and S-wave velocities, is a key element in nuclear structure design. Accordingly, it is important to determine the P- and S-wave velocities in the Gyeongju and Pohang regions of South Korea, which are home to nuclear power plants and have a history of seismic activity. P- and S-wave velocities can be obtained indirectly through a correlation with physical properties (e.g., N values, Young's modulus, and uniaxial compressive strength), and researchers worldwide have proposed regression equations. However, the Gyeongju and Pohang regions of Korea have not been considered in previous studies. Therefore, a database was constructed for these regions. The database includes physical properties such as N values and P- and S-wave velocities of the soil layer, as well as the uniaxial compressive strength, Young's modulus, and P- and S-wave velocities of the bedrock layer. Using the constructed database, the geological characteristics and distribution of physical properties of the study region were analyzed. Furthermore, models for predicting P- and S-wave velocities were developed for soil and bedrock layers in the Gyeongju and Pohang regions. In particular, the model for predicting the S-wave velocity for the soil layers was compared with models from previous studies, and the results indicated its effectiveness in predicting the S-wave velocity for the soil layers in the Gyeongju and Pohang regions using the N values. The proposed models for predicting P- and S-wave velocities will contribute to predicting the damage caused by earthquakes.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.33-43
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• 2020

CO₂ geological storage is currently considered as the most stable and effective technology for greenhouse gas reduction. The saline formations for CO₂ geological storage are generally located at a depth of more than 800 m where CO₂ can be stored in a supercritical state, and an extensive impermeable cap rock that prevents CO₂ leakage to the surface should be distributed above the saline formations. Trough analysis of seismic and well data, we identified the basalt flow structure for potential CO₂ storage where saline formation is overlain by basalt cap rock around PZ-1 exploration well in the Southern Continental Shelf of Korea. To evaluate CO₂ storage capacity of the saline formation, total porosity and CO₂ density are calculated based on well logging data of PZ-1 well. We constructed a 3D geological grid model with a certain size in the x, y and z axis directions for volume estimates of the saline formation, and performed a property modeling to assign total porosity to the geological grid. The estimated average CO₂ geological storage capacity evaluated by the U.S. DOE method for the saline formation covered by the basalt cap rock is 84.17 Mt of CO₂(ranges from 42.07 to 143.79 Mt of CO₂).