• Geophysics and Geophysical Exploration
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• v.3 no.1
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• pp.19-24
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• 2000

Seismic reflection data was obtained by using 28 and 100 Hz geophones at the ground subsidence sites in an old coal mine area. Frequency spectrum of the geophone analyzed with offset revealed that 1) In the near offset ($1\~10m$), the signals in the 100 Hz geophone data contains higher frequency components (up to 300 Hz) than that of the 28 Hz (<200 Hz), 2) In the intermediate offset ($11\~39m$), although the 28 Hz geophone data showed very similar frequency characteristics as the near offset data, the 100Hz geophone data seemed to be contaminated by noise at high frequency zone (>200 Hz). In the far offset ($\geq40\;m$), the signals in both the 28 and 100 Hz geophone data are attenuated to noise level at high frequency Bone more than 150 Hz.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.321-328
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• 2002

Difficulties encountered in downhole S-wave (shear wave) surveys include the precise determination of shear wave travel times and determination of geophone orientation relative to the direction of polarization caused by the seismic source. In this study an S-wave enhancing and a principal component analysis method were adopted as a tool for determination of S-wave arrivals and the direction of polarization from downhole S-wave survey data. An S-wave enhancing method can almost double the amplitudes of S-waves, and the angle between direction of polarization and a geophone axis can be obtained by a principal component analysis. Once the angle is obtained data recorded by two horizontal geophones are transformed to principal axes, yielding so called scores. The scores gathered along depth are all in-phase, consequently, the accuracy of S-wave arrival picking could be remarkably improved. Applying this processing method to the field data reveals that the test site consists of a layered ground earth structure.

• The Journal of Engineering Geology
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• v.3 no.2
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• pp.167-176
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• 1993

The high resolution studies for shallow seismic reflection are carried out using 24-channel seismograph and the high sensitivity geophone(50-500Hz). In order to study the underground structures such as small faults, fractures, cracks and cavities, it is of great importance to enhance high resolution of the seisrnic records for the targets vertically and laterally. In analysis of high resolution seismic reflection, Nyquist frequency($F_N$) should be lager than the highest frequency in the records and the highest wave number should not be exceed the Nyquist wave number($1/2{\Delta}x$). The highest frequency above the Nyquist will be removed using low pass filter or antialias filter. The trace interval Ax should be taken into account so that the highest wave number(f/v) can be less than $1/2{\Delta}x$. The Fraunhofer diffraction of a hyperbola seismic section above the tunnel appeares on the common offset method, and little first arrivals of direct wave on the single-end shooting, delayed strong impulsive reflections are also shown above the tunnel. Ray Method(Cherveney and Psencik, 1983) also represents the same results that the reflected waves from the tunnel are delayed and single impulsive with little first arrivals, while transrnitted waves through the tunnel are delayed with low frequency.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.41-54
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• 2024

Regular monitoring plays a crucial role in ensuring the safety of geotechnical structures. Currently, nondestructive methods are employed to monitor such structures to minimize the impact, e.g., sensor-based accelerometers, displacement meters, image-based lasers, and drone imaging. These technologies can observe surface changes; however, they frequently suffer difficulties in terms of identifying changes in internal properties. To monitor changes in internal properties, in situ geotechnical investigations can be employed. A nondestructive test that can be used for this purpose is the spectral analysis of surface wave (SASW) test using geophones. The SASW test is a nondestructive method; however, due to the time required for data interpretation and the difficulty in analyzing the data, it is challenging to use the SASW test for monitoring applications that require frequent observations. However, it is possible to apply the first-step analysis, which yields the dispersion curve, for monitoring rather than the complete SASW analysis, which yields the shear wave velocity. Thus, this paper presents a fundamental study on the phase difference that derives the dispersion curve to utilize the SASW test for monitoring. The reliability of each phase difference interval is examined to determine the boundary to the subjected monitor. The study used phase difference data obtained using a geophone from a single-layered, homogeneous ground site to evaluate reliable boundaries. The findings of this study are expected to improve the utility of monitoring by identifying the ideal boundary for phase difference data.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.223-226
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• 2005

In order to acquire 3 components data which has the good signal to noise ratio with only one shot, 3-C geophones were used, As a result, the vertical component showed the distinct first arrival of P-wave, and the horizontal component was improved the signal to noise ratio of S-wave, while was attenuated P-wave. The 2-D Poisson's ratio section was computed from P- and S-wave cell velocities included velocity tomograms of the P- and S-waves. The Poisson's ratio values were computed in the range of $0.2{\~}0.3$. With one shot, we can obtain 2-D distribution of dynamic Poisson's ratio as well as velocity tomograms of P- and S-waves.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.95-100
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• 2006

To reveal subsurface structures of the Ulsan fault, seismic data were recorded along a 750-m long line near Nongso-Eup in Ulsan. P and S waves were generated simultaneously by impacting a 5 kg sledgehammer on a tilted plate. The data were received by 16 10-Hz 3-component geophones at 3 m intervals. Refracted P waves were inverted using the tomography method. Dip moveout and migration were applied to reflection data processed following a general sequence. Four layers were identified based on P-wave velocities and P- and S-wave stacked image. From top to bottom, the P-wave velocity of each layer ranges in $300{\sim}1100\;m/s$, $1100{\sim}1700\;m/s$, $1700{\sim}2700\;m/s$, and greater than 2700 m/s. The corresponding thickness of the top three layers averages 3.9 m, 5.9 m, 4.4 m, respectively. The S-wave stack section is effective to define subsurface structures shallower than 10 m.

• Geophysics and Geophysical Exploration
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• v.26 no.3
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• pp.103-113
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• 2023

In the oil and gas exploration market, various cableless seismic systems have been developed as an alternative to improve data acquisition efficiency. However, developing such equipment at a small scale for academic research is not available owing to highly priced commercial products. Fortunately, building and experimenting with open-source hardware enable the academic utilization of cableless seismic equipment with relatively low cost. This study aims to develop a cableless seismic acquisition module using Arduino. A cableless seismic system requires the combination of signal sensing, simple pre-processing, and data storage in a single device. A conventional geophone is used as the sensor that detects the seismic wave signal. In addition, it is connected to an Arduino circuit that plays a role in implementing the processing and storing module for the detected signals. Three main functions are implemented in the Arduino module: preprocessing, A/D conversion, and data storage. The developed single-channel module can acquire a common receiver gather from multiple source experiments.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.209-216
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• 1999

In order to get geologic information necessary for underground installation of water pipe, seismic refraction profiling was applied to the southwest side of the Seomjin River which flows between Namwon-gun, Cholabuk-do and Gokseong-gun, Cholanam-do. Before obtaining the in-line refraction data, walkaway data were recorded with 1 m geophone interval and -36∼+36 m offset range. From the walkaway data, it is interpreted that a dry soil layer with the average velocity of 585 m/s covers wet sediments with the average velocity of 1,326 m/s. The second layer overlies basements nearly horizontally with the average velocity of 4,218 m/s. Refraction profiling of 220 m long with the geophone interval of 2 m is interpreted with the Generalized Reciprocal Method (GRM). Three layers are identified with average velocities of 688 m/s, 1,473 m/s, and 3,776 m/s, respectively. The depth to the bedrock impossible for ripping ranges between two extremes, 1.51∼2.43 m and 2.25∼3.54 m, depending upon thickness of the hidden layer. A typical shortcoming of refraction method, the hidden layer problem, prevents accurate estimation in depth of the second layer.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.209-214
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• 1999

A field experiment generating shear waves by trench method was conducted at two places in Taejun area. We were able to separate the P- and S-waves by summing and subtracting the vertical and horizontal component of the data recorded at a three component downhole geophone in the borehole. The analysis of the records revealed that the shear waves were polarized to NS and EW directions. The faster shear waves were polarized to NS direction. The NS direction generally agrees with the dominant joints direction observed from the cores collected from the borehole.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.412-417
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• 2005

To ensure the safety of the tunnelling without the loss of economy, the tunnel seismic profiling(TSP) method for the prediction ahead of tunnel face, begins to be used routinely in these days. TSP method does not interfere the tunnelling works while the horizontal drilling does, and its prediction length is longer than that of the drilling. Yet the most frequently adopted technique of TSP in Korea is the multi-shot and 2 receiver array using in-hole receivers, even though this array requires as many as 26 drill-holes for receiver installation and ballasting, which results in 3-6 hours of suspension in excavation work. In this paper, multi-receiver and lesser shot array using side-wall attached 3 component geophones is to be described to prove the efficiency in terms of the survey time as well as the reliability of the method by comparison of the predicted weak points and the face mapping results. The predictions mostly agreed with the real fractures or joint developed zones which have been confirmed during the excavation. It also has been found that TSP method can be effectively applied to perform draining ground water ahead of tunnel face by imaging the geologic discontinuities.