• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.41-49
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• 2006

This paper demonstrates the feasibility of using shallow S-wave, high-resolution seismic reflection surveys to characterize geological structure and stratigraphy of basement rocks for civil engineering purposes. S-wave seismic reflections from depths less than 20 m were recorded along the top of steep readout slopes. Seismic reflection data were recorded using a standard CDP acquisition method with a 24-channel seismograph and a sledge-hammer SH-wave source. The data were acquired using a split-spread source-receiver geometry with a 2 m shot-and-receiver interval, and then were processed to enhance S/N ratio of the data, to improve resolvable power of the seismic section, and to get velocity information of the basement rock. The final seismic reflection profiles using the CDP technique has imaged surfaces as shallow as less than 1m and resolved beds as thin as 1m. The migrated reflection sections possess sufficient quality to correlate the prominent reflection events to the bedding planes and faults identified on the readout outcrops. Similar S-wave reflection surveys could also be used to produce the necessary details of a geological structure of shallow bedrocks to pinpoint optimum locations for monitor wells of civil engineering purposes.

• Geophysics and Geophysical Exploration
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• v.25 no.3
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• pp.120-128
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• 2022

There are 17,000 reservoir dams in Korea, of which more than 85% were built over 50 years ago. Old embankment dams are weakened by internal erosion and suffusion phenomena due to preferential leakage paths and this ongoing weakening can cause their failure. Therefore, early warning associated with leakage in an embankment dam is crucial to prevent its failure. An electrical resistivity survey is a non-destructive, real-time and in-situ technique for detecting the development of leakage zones and general conditions of embankment dams. Because of its advantages, the electrical resistivity survey is widely used for reservoir safety inspections. However, the electrical resistivity survey is still not officially included in the precise safety inspection of reservoir dams because it cannot present a quantitative index of dam safety. In this study, we propose a method for calculating the leak index according to the water content evaluated from the electrical resistivity survey and/or induced polarization survey. Particularly, by proposing a quantitative leak index calculation method from monitoring surveys and independent surveys, we provide a theoretical basis for including electrical resistivity and induced polarization surveys as components of the precise safety inspection of reservoirs dams.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.111-116
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• 2012

Far-infrared observations provide crucial data for the investigation and characterisation of the properties of dusty material in the Interstellar Medium (ISM), since most of its energy is emitted between ~ 100 and $200{\mu}m$. We present the first all-sky image from a sensitive all-sky survey using the Japanese AKARI satellite, in the wavelength range $50-180{\mu}m$. Covering > 99% of the sky in four photometric bands with four filters centred at $65{\mu}m$, $90{\mu}m$, $140{\mu}m$, and $160{\mu}m$ wavelengths, this achieved spatial resolutions from 1 to 2 arcmin and a detection limit of < 10 MJy $sr^{-1}$, with absolute and relative photometric accuracies of < 20%. All-sky images of the Galactic dust continuum emission enable astronomers to map the large-scale distribution of the diffuse ISM cirrus, to study its thermal dust temperature, emissivity and column density, and to measure the interaction of the Galactic radiation field and embedded objects with the surrounding ISM. In addition to the point source population of stars, protostars, star-forming regions, and galaxies, the high Galactic latitude sky is shown to be covered with a diffuse filamentary-web of dusty emission that traces the potential sites of high latitude star formation. We show that the temperature of dust particles in thermal equilibrium with the ambient interstellar radiation field can be estimated by using $90{\mu}m$, $140{\mu}m$, and $160{\mu}m$ data. The FIR AKARI full-sky maps provide a rich new data set within which astronomers can investigate the distribution of interstellar matter throughout our Galaxy, and beyond.

• Geophysics and Geophysical Exploration
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• v.8 no.2
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• pp.119-128
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• 2005

The assessment of erosional and depositional patterns near bridge piers is essential to understand the fluvial scour process. Geophysical surveys are particularly effective in determining the riverbed variations in a river and may also be of value for obtaining the previous scour history below the riverbed profile. In this study, GPR (Ground Penetrating Radar), as a non-destructive geophysical technique, was used to assess the existence and depth of existing and infilled scour thickness, streambed materials, and pre- and post- scour surfaces at the bridge piers in Han River, June 2002 and October 2002. The GPR acquisition system used for obtaining profiles of the shallow subsurface deposits was a portable GSSI SIR 2000 system with 100 and 400 MHz antennas. The GPR data obtained along the 24 bridge piers in the flow direction of the river and in the surroundings of 5 bridge piers were compared and presented in this study. It is concluded that GPR surveys can be effective in determining both the water depth and sub-bottom geological structure near the bridge piers and abutments provided that the appropriate instrumentation and operational procedures are applied.

• Economic and Environmental Geology
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• v.48 no.5
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• pp.401-408
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• 2015

The achievements of Tateiwa Iwao's work in Korea are assessed as follows. Firstly, he pioneered the practice of stratigraphy in the Korean peninsula and completed geological maps of 21 sheets at 1:50,000 scale. Secondly, he published the results of a geological survey as bulletins, technical reports, and papers. Thirdly, he faithfully carried out the handover of assets and research outputs to Korea. Finally, after returning to Japan, Tateiwa wrote a book entitled The Korea-Japanese Tectonic Zone: History of a Geological Survey in Korea. However, he neglected to educate and train the next geologists for conducting geological surveys and exploration in Korea.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.78-84
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• 2008

Recent earthquakes near nuclear power plants in Korea have triggered public concerns about possible seismicity of the Ulsan Fault Zone in the south-eastern part of the Korean peninsula. To reveal subsurface structures of this fault zone, we conducted high-resolution seismic refraction and reflection surveys, and closely spaced gravity measurements in the Dongchon River valley north of Ulsan, Korea. Here alluvium covers the north-south trending fault zone in a 1-km wide valley. Both source points and receivers were spaced at 5-m intervals for the 24-channel seismic refraction and reflection methods, along two profiles of 835 m and 415 m length. Gravity data were also measured along these profiles at 131 stations using a 10-m interval. Synergetic interpretation of seismic refraction, high-resolution seismic reflection, and gravity surveys across the valley indicates that the Ulsan Fault Zone was formed by apparent north-south strike-slip motions during the Cretaceous, and that some faults may have been reactivated by east-west compressional or transpressional stresses during the Tertiary or Quaternary.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.60-67
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• 2008

In this paper we consider an application of the method of electromagnetic (EM) migration to the interpretation of a typical marine controlled-source (MCSEM) survey consisting of a set of sea-bottom receivers and a moving electrical bipole transmitter. Three-dimensional interpretation of MCSEM data is a very challenging problem because of the enormous number of computations required in the case of the multi-transmitter and multi-receiver data acquisition systems used in these surveys. At the same time, we demonstrate that the MCSEM surveys with their dense system of transmitters and receivers are extremely well suited for application of the migration method. In order to speed up the computation of the migration field, we apply a fast form of integral equation (IE) solution based on the multigrid quasi-linear (MGQL) approximation which we have developed. The principles of migration imaging formulated in this paper are tested on a typical model of a sea-bottom petroleum reservoir.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.92-100
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• 1998

Array CSAMT surveys were conducted in two areas where it was not easy to identify the presence of faults only with geological survey because of thick overburden. The purpose of these surveys were to locate the faults and to delineate the deep resistivity structures around the faults. The steep dip lineaments having high contrast in resistivity laterally and the low resistive zones having some width in the resistivity sections were interpreted as faults and fracture zones associated with faults, respectively, The good applicability of array CSAMT to the investigation of fault was recognized owing to the agreement between the interpretation results of array CSAMT and the conclusive evidences collected by the following geological survey. The evidences includes the recent exposure of fault and the trajectory of fault evidences of the survey line. A comparison of the applicabilities of array CSAMT method and the resistivity method using dipole-dipole array was presented with the results of both methods along a same traverse line.

• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.59-66
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• 2016

The electrical resistivity method is an effective geophysical tool to detect subsurface contamination because the contaminated zones show generally lower electrical resistivity. In this study, the electrical resistivity surveys were applied to a waste landfill site to image the subsurface structure around the landfill and to identify the contaminated zones. First, the dipole-dipole 2D resistivity surveys were conducted along the boundaries of landfill to define the developed contaminated zones. Then the crosshole resistivity tomography was applied to confirm the suspected contaminated zones at depth. The results of drilling and geochemical analysis of ground water supported that the low resistivity zones coincide well with the contaminated zones and the leachate pathways could be delineated effectively from the resistivity survey.

• Geophysics and Geophysical Exploration
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• v.27 no.2
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• pp.129-143
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• 2024

In magnetotelluric (MT) surveys, small inhomogeneities near the surface cause a static shift in which apparent resistivities shift regardless of frequency. As the static shift in MT data leads to errors in subsurface structure interpretation, many studies have been conducted over the past few decades to mitigate or remove the distortions it caused. The most representative method involves removing static shifts from the data before inversion. Conversely, static shifts can be corrected during inversion or included in the inversion process. In addition, other geophysical data can be used to remove static shifts. However, the correction methods are limited to one-dimensional (1D) static responses, and limitations remain in two- or three-dimensional (2D or 3D) interpretation of distorted MT data owing to static shifts. This study provides a foundation for future studies on static shift by analyzing several previously published methods.