• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.184-196
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• 2008

We perform MT soundings in Bendigo, the northern part of Victoria, Australia, to investigate the deep subsurface geologic structure. The primary purpose of this survey is to figure out whether the discontinuity such as faults extends northward. The time series of MT signal were measured over 11 days at 71 measurement stations together with at remote reference, which help enhance the quality of impedance estimation and its interpretation. The impedances are estimated by robust processing using remote reference technique and then inverted with 2D MT 2D inversion. We can see that known faults are clearly imaged in MT 2D inversion. Comparing resistivity images from MT 2D inversion with interpreted boundary from reflection seismic exploration, two interpretations match well each other.

• Journal of Soil and Groundwater Environment
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• v.28 no.spc
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• pp.18-39
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• 2023

Rapid development of geophysical exploration and hydrogeologic monitoring techniques has yielded remarkable increase of datasets related to groundwater systems. Increased number of datasets contribute to understanding of general aquifer characteristics such as groundwater yield and flow, but understanding of complex heterogenous aquifers system is still a challenging task. Recently, applications of data science technique have become popular in the fields of geophysical explorations and monitoring, and such attempts are also extended in the groundwater field. This work reviewed current status and advancement in utilization of data science in groundwater field. The application of data science techniques facilitates effective and realistic analyses of aquifer system, and allows accurate prediction of aquifer system change in response to extreme climate events. Due to such benefits, data science techniques have become an effective tool to establish more sustainable groundwater management systems. It is expected that the techniques will further strengthen the theoretical framework in groundwater management to cope with upcoming challenges and limitations.

• Journal of the Korean Geophysical Society
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• v.7 no.3
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• pp.217-224
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• 2004

20 groundwater samples in Sahagu Busan were analyzed to understand the characteristics of groundwater quality of the area. Using the data, physical and chemical property, mineral contents, water-rock reaction of the groundwater carried out. The water type in the area is Ca2+-HCO3- and Ca2+-(Cl-+SO42-). Average EC value of the groundwater is 540μS/cm, but in the case of several samples influenced by eawater, the value is up to 4,140μS/cm. Some samples are exceeding the drinking water tandard in NO3-N and NH4-N. On the other hand, contamination by heavy metal is not found.

• Journal of the Korean Geophysical Society
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• v.7 no.2
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• pp.121-134
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• 2004

This study has tried to develop the modified DRASTIC Model by supplying the parameters, such as structural lineament density and land-use, into conventional DRASTIC model, and to predict the potential of groundwater contamination using GIS in Hwanam 2 District, Gyeonggi Province, Korea. Since the aquifers in Korea is generally through the joints of rock-mass in hydrogeological environment, lineament density affects to the behavior of groundwater and contaminated plumes directly, and land-use reflect the effect of point or non-point source of contamination indirectly. For the statistical analysis, lattice-layers of each parameter were generated, and then level of confidence was assessed by analyzing each correlation coefficient. Groundwater contamination potential map was achieved as a final result by comparing modified DRASTIC potential and the amount of pollutant load logically. The result suggest the predictability of contamination potential in a specified area in the respects of hydrogeological aspect and water quality.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.13-20
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• 2008

Magnetic method is rapid, cheap and simple geophysical exploration technique, and has wide range of applications such as resources prospecting, geological structure investigation and even geotechnical and environmental problems. Documents during Japanese occupation says that magnetic method was used for exploring metallic ore deposits and hot spring, and that a geomagnetic observatory was operated. From mid 1950's, magnetic explorations for natural resources such as metallic ore, uranium, coal, and groundwater were intensively executed for industrialization. Magnetic survey techniques were rapidly advanced during 1970's and 1980's with improvements of instruments, growth of geophysical manpower, and availability of computers. Decline of mining industry since mid 1980's moved the exploration objects from traditional resources to new ones such as groundwater and geothermal resources. Recently appeared applications such as natural hazard assessment, and engineering and environmental studies increased the magnetic method's utility in the realm of exploration.

• Geophysics and Geophysical Exploration
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• v.7 no.3
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• pp.197-206
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• 2004

Because the minute displacement of ground accompanied by excessive pumping of groundwater at specified site is mainly generated from ill-balancing of water budget within groundwater basin, It is necessary to monitor the variation of micro-subsidence for a long time at representative points. We made up the conceptual model using two-dimensional electrical resistivity survey and three-dimensional soil profile consisted of loam and sand. In verifying the reliability of this conceptual model using numerical modeling for ground settlement and groundwater flowing, two-dimensional electrical resistivity survey with short distance of electrode following soil sampling with hand auger would be useful for interpreting hydrogeological structure related to the minute displacement of ground consisted of loam and sand.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.344-351
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• 2003

Hydrogeological survey and geochemical analysis were carried out in Phra Yun area, Northeast Thailand, which is a typical salt-affected area for an understanding of hydrogeological groundwater behaviours. Geological survey reveals the presence of G1 and F1 faults. Electromagnetic ground conductivity prospecting shows that the high conductivity zones of 15 mS/cm or more are distributed at underground of the G1 and F1 faults where saline groundwater is discharged. The distribution patterns of tritium concentration show that high tritium concentration zones of groundwater were recharged from pond and river. On the assumption that the annual average tritium concentration of precipitation in Northeast Thailand is same as tritium concentration of precipitation in Tokyo and groundwater flows as piston flow, the age of recharging precipitation of groundwater with 15 TU in 1997 could be estimated at 1967-1970 years. The velocity of groundwater flow was calculated to be $5.3{\times}10^{-7}\;m/s\;and\;2.1{\times}x10^{-6}\;m/s$ respectively from a duration time of 30 years and distance of groundwater flow 500m -2000m from the pond and river to the investigation wells. Because the estimated values of velocity of groundwater flow are compatible with the hydraulic conductivities, it is considered that 30 years is a reasonable period for recharging groundwater.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.361-368
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• 2007

In this paper, we suggested the relationship between resistivity of coastal groundwater and NaCl equivalent salinity for the quantitative interpretation the results of surface/borehole resistivity and electromagnetic data. 38 groundwater samples having electrical conductivity higher than about 1,000 ${\mu}S/cm$ were analyzed to derive the empirical relationship between groundwater resistivity and NaCl equivalent salinity. We used Schlumberger chart GEN-8 to convert ion concentration from hydrochemical analysis to the equivalent NaCl salinity, and the portable meter to measure the in situ electrical conductivity of groundwater samples. From the hydrochemical analysis, relationship between the groundwater resistivity $(R_w)$ and equivalent NaCl salinity (Eq_NaCl) is expressed as Eq_NaCl=$5935.3551{\times}R_w^{-1.0993}$, and relationship between the groundwater electrical conductivity (EC) and total dissolved solids (TDS) is expressed as TDS=0.721*EC. We believe these relationships are very useful to assess the seawater intrusion in western and southern coastal area.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.261-266
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• 2007

An efficient three-dimensional (3D) inversion of magnetotelluric (MT) data can be carried out by using approximate sensitivities or avoiding the calculation of a full sensitivity matrix. In this paper, we propose approximate sensitivities for efficient 3D MT inversion based on the Gauss-Newton method and test and compare four kinds of sensitivities. Applying the four sensitivities to both synthetic and field data shows that the effects of sensitivities are highly dependent on data and thus applying various combinations of sensitivities is recommended for efficient inversion and good images.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.335-339
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• 2003

The estimation of seawater intrusion into deep aquifers has been becoming an important subject in terms of site characterization for geological disposal of radioactive waste. Conventional direct-current resistivity methods have been used for ground water explorations and recently have been applied to environmental problems. However, electromagnetic methods are more practical and useful for such a deep investigation. We consider audio-frequency magnetotelluric (AMT) and surface-to-borehole electromagnetic (EM) tomography methods as promising tools for the investigation of deep aquifer. These methods were tested in the Hasunuma area, Chiba Prefecture, Japan. Although the study area is in an urban area, high-quality AMT data were acquired, which was mainly accomplished by night-time data recording and remote-reference data processing. One-dimensional inversion results of the AMT data revealed two extremely conductive zones, which is consistent with the electrical conductivity profile of pore water in core samples. It can be interpreted as the seawater intrusions into both zones. However, the chemical analysis of the groundwater sampled in the deep zone suggests that this groundwater must be fossil seawater that had been confined during sedimentation processes. In addition, the permeability coefficient of the deep layer is very low. Thus the deep conductive zone corresponds to the fossil seawater regarded as being difficult to flow.