• Journal of the Korean earth science society
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• v.30 no.4
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• pp.401-408
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• 2009

We carried out the Suspension PS log and gamma-gamma log in andesite and sedimentary rocks distributed near the area of Myodo-dong, Yeosu. The main purpose of this study was to find out the distribution of seismic velocities and densities and to analyze the correlation of the two rocks by comparing their geophysical well logs with rock cores. The distributions of P and S-wave velocities for two rocks represented in the study area showed a difference of about 2,000 m/sec and 1,500 m/sec with depth, respectively, while the distributions of densities had a discrepancy of about $0.35g/cm^3$ with depth. However, the results of geophysical well logs analysis were similar to the two rocks. Consequently, it is clear that these results are interpreted as a difference due to weathering rather than rock type. In particular, the RQD values showed a good correlation to geophysical well log data.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.507-522
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• 2021

Specific survey objectives often cannot be met using only one geophysical method, as each method's results are influenced by the specific physical properties of subsurface materials. In particular, areas susceptible to geological hazards require investigation using more than one method in order to reduce risks to life and property. Instead of analyzing the results from each method separately, this work develops a four-quadrant criterion for classifying areas of levees as safe or weak. The assessment is based on statistically determined thresholds of seismic velocity (P-wave velocity from seismic refraction and S-wave velocity from multichannel analysis of surface waves) and electrical resistivity. Thresholds are determined by subtracting the standard deviation from the mean during performance testing of this correlation technique applied to model data of four horizontal and inclined fracture zones. Compared with results from the crossplot of resistivity and P-wave velocity, crossplot analysis using resistivity and S-wave velocity data provides more reliable information on the soil type, ground stiffness, and lithological characteristics of the levee system. A loose and sandy zone (represented by low S-wave velocity and high resistivity) falling within the second quadrant is interpreted to be a weak zone. This interpretation is well supported by the N values from standard penetrating test for the central core.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.83-105
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• 2003

Geochemical studies on the alluvial aquifer system near the Nakdong River were carried out for the basic investigation of the estimation of artificial recharge for the river bank filtration. In-situ data do not show any distinct difference between the pumping well and river. Most of waters belong to $_3$ and Ca-$SO_4$ types and show high Mn concentration. In the borehole installed with Multi-Ca-HCOPacker (MP) system, Na, Ca, Mg, $HCO_3$ contents of the groundwater are increased with depth increasing. Cl and $SO_4$ contents of the groundwater show the lowest values at the bottom level (18m depth) and Mn content is very high at the middle level (13.5 m depth) of MP system. There is no distinct difference in the ${\delta}^{18}O$ and D values and tritium content between MP, borehole and surface water samples. The sulfur isotope data indicate that the possible sulfur source is dissolution of sulfate mineral from sedimentary rock. Strontium isotope ratio shows a little differences between the pumping well and observation borehole samples. Nitrogen isotope data indicate that the nitrogen of water samples is originated from fertilizer or organic materials.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.4
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• pp.307-327
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• 2008

Geochemical study on the rocks and minerals of the Gyeongju low and intermediate level waste repository was carried out in order to provide geochemical data for the safety assessment and geochemical modeling. Polarized microscopy, X-ray diffraction method, chemical analysis for the major and trace elements, scanning electron microscopy(SEM), and stable isotope analysis were applied. Fracture zones are locally developed with various degrees of alteration in the study area. The study area is mainly composed of granodiorite and diorite and their relation is gradational in the field. However, they could be easily distinguished by their chemical property. The granodiorite showed higher $SiO_2$ content and lower MgO and $Fe_2O_3$ contents than the diorite. Variation trends of the major elements of the granodiorite and diorite were plotted on the same line according to the increase of $SiO_2$ content suggesting that they were differentiated from the same magma. Spatial distribution of the various elements showed that the diorite region had lower $SiO_2,\;Al_2O_3,\;Na_2O\;and\;K_2O$ contents, and higher CaO, $Fe_2O_3$ contents than the granodiorite region. Especially, because the differences in the CaO and $Na_2O$ distribution were most distinct and their trends were reciprocal, the chemical variation of the plagioclase of the granitic rocks was the main parameter of the chemical variation of the host rocks in the study area. Identified fracture-filling minerals from the drill core were montmorillonite, zeolite minerals, chlorite, illite, calcite and pyrite. Especially pyrite and laumontite, which are known as indicating minerals of hydrothermal alteration, were widely distributed in the study area indicating that the study area was affected by mineralization and/or hydrothermal alteration. Sulfur isotope analysis for the pyrite and oxygen-hydrogen stable isotope analysis for the clay minerals indicated that they were originated from the magma. Therefore, it is considered that the fracture-filling minerals from the study area were affected by the hydrothermal solution as well as the simply water-rock interaction.

• Journal of the Korean GEO-environmental Society
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• v.13 no.10
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• pp.15-23
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• 2012

A numerical model and field monitoring data are used to estimate a change in groundwater level at a borrow site, which will be constructed at the mountainous area with a large ground excavation in the study area, Hwaseong city. Lithologic data and hydraulic coefficients are collected at 9 boreholes and also groundwater levels are measured at these boreholes and existing wells in the study area. Additionally, groundwater recharge rate for the type of land cover is estimated using water budget analysis; 133.34mm/year for a mountainous area, 157.68mm/year for a farming area, 71.08mm/year for an urbanized area, and 26.06mm/year for a bedrock exposure area. The change in groundwater level in and around a borrow site is simulated with Modflow using these data. The result of a transient model indicates that a removal of high ground (over 40El.m) by an excavation will produce a decrease in groundwater levels, up to 1 m, around a borrow site in 10 years. It also explains that this ground excavation will bring about the decreases of 9.4% and 7.0% for groundwater recharge and surface runoff, respectively, which are the factors causing groundwater level's change. This study shows that it is required to construct the groundwater monitoring wells to observe the change of groundwater near a borrow site.

• Journal of the Korean earth science society
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• v.42 no.1
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• pp.39-54
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• 2021

Damyang Wetland, a riverine wetland, has been designated as the first wetland protection area in South Korea and is a candidate area for the Mudeungsan Area UNESCO Global Geopark. The Damyang Wetland area is the upstream part of the Yeongsan River and is now a relatively wide plain. To reconstruct the sedimentary environment around the Damyang Wetland, core samples were obtained, and sedimentary facies analysis, AMS and OSL age dataings, grain size, and geochemical analyses were carried out. In addition, comprehensive sedimentary environment changes were reconstructed using previous core data obtained from this wetland area. In the Yeongsan River upstream area, where the Damyang Wetland is located, fluvial terrace deposits formed during the late Pleistocene are distributed in an area relatively far from the river. As a gravel layer is widely distributed throughout the plains, Holocene sediments were likely deposited in a braided river environment when the sea level stabilized after the middle Holocene. Then, as the sedimentary environment changed from a braided river to a meandering river, the influx of sand-dominated sediments increased, and a floodplain environment was formed around the river. In addition, based on the pollen data, it is inferred that the climate was warm and humid around 6,000 years ago, with wetland deposits forming afterward. The the trench survey results of the river area around the Damyang Wetland show that a well-rounded gravel layer occurs in the lower part, covered by the sand layer. The Damyang Wetland was likely formed after the construction of Damyang Lake in the 1970s, as muddy sediments were deposited on the sand layer.

• Geophysics and Geophysical Exploration
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• v.21 no.4
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• pp.255-261
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• 2018

The purpose of this study was to obtain a large amount of saline groundwater around coastal aquaculture farms. Thus, we have proposed a method for evaluating the potential amount of saline groundwater resources through the combined analysis of geophysical methods. Refraction seismic survey and electrical resistivity survey were conducted in the vicinity of fish farm at Hadong, Gyeongnam Province. As the result, the velocity of layer in the range of 900 ~ 2,400 m/s was found to be saltwater aquifer with high water content. Geological drilling investigation and analysis of soil samples also showed that the soil at study area was the same as the texture of sandy loam layer in agricultural radial collector wells installed by KRC (Korea Rural Community Corporation). Futhermore, the study area turned out to be quite possible to develop saline groundwater from the coastal shallow aquifer. Therefore, parallel analysis of refraction seismic surveys and electrical resistivity surveys at coastal area are expected to be very useful for the detection of the aquifer composed of sand and gravel layers with high porosity in sandy sedimentary layers along the coastal area.

• Journal of the Korean GEO-environmental Society
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• v.22 no.12
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• pp.33-40
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• 2021

The deterioration of underground facilities, disturbance of the ground due to underground development activities, and changes in ground water can cause ground subsidence accidents in the urban areas. The investigation on the geotechnical and hydraulic factors affecting the ground subsidence accident is very significant to predict the ground subsidence risk in advance. In this study, an analysis DB was constructed through 3D ground modeling to utilize the currently operating geotechnical survey information DB and ground water behavior information for risk prediction. Additionally, using these results, the relationship between the actual ground subsidence occurrence history and ground conditions and ground water level changes was confirmed. Furthermore, the methodology used to visualize the risk of ground subsidence was presented by reconstructing the engineering characteristics of the soil presented according to the Unified Soil Classification System (USCS) in the existing geotechnical survey information into the internal erosion sensitivity of the soil, Based on the result, it was confirmed that the ground in the area where the ground subsidence occurred consists of more than 40% of sand (SM, SC, SP, SW) vulnerable to internal erosion. In addition, the effect of the occurrence frequency of ground subsidence due to the change in ground water level is also confirmed.

• The Korean Journal of Quaternary Research
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• v.19 no.1
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• pp.1-17
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• 2005

This study aims to study the distribution and formation age of Quaternary deposits in the downstream of Yeongsan Estuarine River, encompassing Muan, Illo and Donggang counties. For this purpose the authors examine several borehole data, and step trench survey for excellent profiles was studied in connection with grain size population and magnetic susceptibility. As a result, it is interpreted that the coastal plain of the Yeongsan River was formed by sea level rise after Last Glacial Maximum(LGM). The fore edge/escarpment of coastal terraces distributed 7-10 m asl is assumed to be formed during the last glacial period, while the coastal terraces distributed above 7-10m asl formed during MIS 5a. In addition, the fore edge/escarpment of coastal terraces distributed above 15 m asl is presumed to be have been formed during the stadial of last interglacial period, while the formation age of coastal terraces distributed above 15m(asl) is assumed to be MIS 5e. This formation age can be estimated by the coastal terrace ages of the southeastern coast of Korean Peninsula. The characteristics of Quaternary deposits linked to paleolithic culture will eventually lead to the reconstruction of ecosystem environment of paleolithic peoples.

• Economic and Environmental Geology
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• v.56 no.3
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• pp.343-363
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• 2023

Sulawesi island, as a global producer of nickel resources, is leading the rapid growth of nickel industry of Indonesia. Nickel laterite deposits in Sulawesi was formed by lateritization of the world-scale East Sulawesi Ophiolite (ESO) under the active tectonic setting and tropical rainforest climate. In this paper, exploration cases for nickel laterite deposits in five regions of Sulawesi are reported. Regional characteristics on nickel laterite deposits in Sulawesi are understood based on various exploration activities such as outcrop, trench and pit survey, petrological observation, geochemical analysis, and interpretation of drilling data, etc.. In the northeastern part of 'Southeast-Arm', which is a strategic location for nickel industry of Indonesia, ESO is extensively exposed to the surface. In the Morombo and Morowali regions, typical high-grade saprolite-type orebodies with a thickness of 10 to 20 m occur. The cases showed that topographic relief tends to regulate Ni-grade distribution and orebody thickness, and that high grade intervals tend to occur in places where joints and garnierite veins are dense. In the Tinanggea and South Palangga regions in the southern part of the Southeast-Arm, overburden composed of Neogene to Quaternary deposits is a major factor affecting the preservation and profitability of nickel laterite deposits. Despite the overburden, high-grade saprolite-type orebodies composed of Ni-bearing serpentine with garnierite veins occur in a thickness of around 10 m to secure economic feasibility. In contrast, in the Ampana region in the northern part of 'East-Arm', low-grade nickel laterite deposits with immature laterite profile was identified, which is thought to be the result of active denudation due to tectonic uplift. Exploration cases in this paper will help to understand characteristics and controlling factors on nickel laterite deposits in Sulawesi, Indonesia.