• The Journal of Engineering Geology
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• v.2 no.2
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• pp.113-130
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• 1992

Groundwater in crystalline basement is controlled primarily by tectonic fractures. It is evident that the delineation of the heavily faulted area and/or fractures deeply developped should be considerable value in deep-seated low enthalphy geothermal water. Electrical and electromagnetic methods have effectively been employed to map hydraulic faults and shear zones for groundwater exploration. In this study VLi; dipoledipole resistivity, controlled source audio~frequency magneto-telluric(CSAMT) and magnetic methods were applied in the Bomun resort area, adjacent to Kyongju city, southeastern part of Korea. The integrated geophysical tools employed in this experiment can be manifested themselves as: 1. Magnetic high for granite intrusions which is more favorable for geothermal gradient increase in depth. 2. VLF cross-over trends for mapping linear shallow conductive fractures and shear zones. 3. Dipole-dipole resistivity distributions for the deep-seated(less than 500m in depth) fractures and shear zones. The dipole-dipole resistivity field data were inverted to the true resistivity distribution with two-dimensional automatic inversion program based on the finite-difference method. 4. CSAMT provides an efficient way of delineating fractures and fault zones if the depth is greater than about 500m.

• Geophysics and Geophysical Exploration
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• v.4 no.1
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• pp.1-7
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• 2001

The application of geophysical survey methods need to be integrated to meet the increasing demands of imaging of the subsurface in the practical application of civil engineering, underground water survey and environmental problems. This paper examines the IP survey which can be surveyed simultaneously with DC resistivity survey. In this study, 3-D IP modeling algorithm was developed. The 3-D IP modeling algorithm was based on 3-D resistivity modeling by finite-element method. The result of 3-D modeling was compared with 2-dimensional modeling result. The result showed that the 3-D modeling algorithm developed in this study was accurate. Finally, the 3-D modeling algorithm developed in this paper will be useful for the study of IP data.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.22 no.1
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• pp.1.2-5
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• 1994

Ionospheric sounding experiments have been conducted at RRL (Radio Research Laboratory), Ministry of Communications, using Digisonde 256 since its installation in 1990. Routine observations of the vertical sounding are carried out 48 times (or 39 times) a day, at every 24 hour. In addition, we also made oblique sounding experiments to obtain the real time data of Maximum Usable Frequency (MUF) and detect the anomalous HF propagation, as a part of the joint study between RRL and CRL (Communications Research Laboratory) of Japan. The two stations involved in the study were Anyang (RRL, Korea) and Kokubunji (CRL, Japan). The ionosondes used in both stations were Digisonde 256, developed by ULCAR (University of Lowell, Center for Atmospheric Research), U. S. A. , and the synchronization of time was accomplished with the help of GPS receiver. During most part of the experiments RRL transmitted non-modulated pulses, and CRL received them. The experiment was scheduled from October 25 through October 29, 1993. However, the ionosphere was not developed well enough to conduct the experiment with pre-set operation parameters. The experiment became successful (from 0500 UT to 0800 UT, October 29) only after the operation parameters had been changed, and the continuous ionograms were obtained by CRL at 0718 UT and 0733 UT in October 29, 1993. We believe this type of experiment will ensure the qualitative enhancement of solar-terrestrial physics research and a routine observation of the oblique ionospheric sounding. In this report, we present the results of the fore-mentioned oblique sounding as well as the vertical sounding results obtained by Digisonde 256 at Anyang station of RRL.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.23 no.1
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• pp.34-38
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• 1995

A diagnostic study on the summertime air mass thunderstorms occurring in the middle region of South Korea was made by analyzing the data of surface and upper air observations as well as the surface and upper level weather charts. The key parameters used in the present study are the amount of precipitable water below 850 hPa level, the vertical profiles of water vapor content and wind, and both the temperature difference and the equivalent potential temperature difference between 850 hPa and 700 hPa levels. It is found from this study that the summertime air mass thunderstorms in the middle region of South Korea can be classified into two distinct types, type I and type II. The thunderstorms of type I occur under the atmospheric conditions of high moisture content, low vertical wind shear in low levels, and conditional instability between 850 hPa and 700 hPa levels. On the other hand, the thunderstorms of type II occur under the atmospheric conditions of less moisture content, higher wind shear and conditional instability. Furthermore, our study suggests that atmospheric instability and the amount of water vapor below 850 hPa level are complementary in the development of air mass thunderstorms. The complementary nature between these two parameters may be an explanation for the thunderstorm development in the areas of low atmospheric water vapor content such as the plains of eastern Colorado.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.23 no.1
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• pp.39-51
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• 1995

Bidirectional transport trend using the sediment-transport path model was identified in the two areas, sand ridge area and tidal mudflat in Garolim Bay, which is located in the mid-western coast of Korean Peninsular. This model exhibits the two-dimensional view of clear sediment transport trend based on data of changes in sediment statistics such as mean, sorting, and skewness, Garolim Bay was selected to test for the sediment-transport path model developed by McLaren and Bowles [1985]. Line-S, a typical tidal mudflat and representative of the Garolim Bay tidal flats, is well tested by this model, showing a clear seasonal change and coarsening-trend seaward (case C). This indicates that strong ebb currents carried relatively coarser sediments seaward with respect to high energy regime. Seasonally, this energy regime slowly decreases toward the summer in contrast with an increase of energy regime of flood tides, carrying coarser sediments landward (case C) in the summer. However, the Line-D area does not show consistent transport trend with respect to time-series. Separated and scattered events show fining trend landward (case B) in the sand ridge itself. The finining-trend (case B) either seaward and landward is not chiefly important in both the entire Line-D area and sand ridge itself. Also, the coarsening-Trend (case C) landward is not significant in the sand ridge itself. Consequently, in reality, the selection of suitable and representative locations are very important to fit with this model.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.49-56
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• 2000

As a part of geophysical studies on segmentation of the Ulsan fault, walkaway refraction seismic data were measured at 17 stations near National Road 7 between Kyungju and Ulsan. Seismic anisotropy was analyzed in the offset range of 1-48 m. The average refraction velocity of 1787 m/s indicates the refractor is the upper boundary of weathered basement. P-wave anisotropy is computed to be 0.056 in average, which may serve as a weak evidence that the strike of major geologic structure coincide with the inferred fault direction. In the south of the province boundary between Kyungsangnam-do and Kyungsangbuk-do, the velocity anisotropy is normal in that P-wave velocity in the strike direction is faster than the one measured in the dip direction. On the contrary, it appears that the fault strikes in many directions or that fractures may be developed better in the dip direction in the northern par. Such a difference in anisotropic pattern is believed to be a seismic evidence indicating that a segmentation boundary of the Ulsan fault locates near the province boundary.

• Journal of the Korean Geophysical Society
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• v.4 no.2
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• pp.113-120
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• 2001

The discrete wavelet transform(DWT) has potential as a tool for supplying discriminatory attributes with which to distinguish seismic events. The wavelet transform has the great advantage over the Fourier transform in being able to localize changes. In this study, a discrete wavelet transform is applied to seismic traces for identifying seismic events and picking of arrival times for first breaks and S-wave arrivals. The precise determination of arrival times can greatly improve the quality of a number of geophysical studies, such as velocity analysis, refraction seismic survey, seismic tomography, down-hole and cross-hole survey, and sonic logging, etc. provide precise determination of seismic velocities. Tests for picking of P- and S- wave arrival times with the wavelet transform method is conducted with synthetic seismic traces which have or do not have noises. The results show that this picking algorithm can be successfully applied to noisy traces. The first arrival can be precisely determined with the field data, too.

• 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.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.26 no.1
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• pp.43-58
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• 1998

The Kwinana Shoreline Fumigation Experiment (KSFE) took place at Fremantle, WA, Australia between January 23 and February 8, 1995. The CSIRO DAR LIDAR measured plume sections from near the Kwinana Power Station (KPS) stacks to up to about 5 km downstream. It also measured boundary layer aerosols and the structure of the boundary layer on some occasions. Both stages A and C of KPS were used as tracers at different times. The heart of the LIDAR system is a Neodymium-doped Yttrium-aluminum-garnet (Nd:YAG) laser operating at a fundamental wavelength of 1064 nm, with harmonics of 532 nm and 355 nm. For these experiments the third harmonic was used because the UV wavelength at 355 nm is eye safe beyond about 50 m. The laser fires a pulse of light 6 ns in duration (about 1.8 m long) and with an energy (at the third harmonic) of about 70 mJ. This pulse subsequently scattered and absorbed by both air molecules and particles in the atmosphere. A small fraction of the laser beam is scattered back to the LIDAR, collected by a telescope and detected by a photo-multiplier tube. The intensity of the signal as a function of time is a measure of the particle concentration as a function of distance along the line of the laser shot. The smoke plume was clearly identifiable in the scans both before and after fumigation in the thermal internal boundary layer (TIBL). Both power station plumes were detected. Over the 9 days of operation, 1,568 plumes scans (214 series) were performed. Essentially all of these will provide instantaneous plume heights and widths, and there are many periods of continuous operation over several hours when it should be possible to compile hourly average plume statistics as well. The results of four days LIDAR observations of the dispersion of smoke plume in the TIBL at a coastal site are presented for the case of stages A and C.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.155-165
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• 2002

This paper presents a case study on the construction of a long tunnel named as "Solan tunnel", which connects between Mt. Dongbaek station and Dokye station in the Youngdong Railroad. The tunnel will be the longest tunnel with length of 16.4 km in Korea when completed. The tunnel site is located in a complex geological region with faults, cavities and coal measures. In construction of adit No. 2, geophysical investigation methods such as electrical resistivity method and GPR(Ground Penetration Radar) were used to detect faults, cavities and coal measures in advance with some success. The geophysical investigation results and in-situ boring data were used as feedback to improve tunnel reinforcement design. Also, the tube umbrellas of grouted steel pipes were found to have a good reinforcement and grouting effects in zones of faults, cavities. In zones of coal measures, swellex rockbolts with mortar grouting were verified as successful.