• Title/Summary/Keyword: geophysics

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Conversion of 3-Component Magnetic Data into Geodetic Coordinate System by Using Clinometer and GNSS Compass (경사계와 GNSS 나침반을 이용한 3성분 자력 탐사자료의 측지 좌표계로의 변환 방법)

  • Jeon, Tae-Hwan;Rim, Hyoungrea;Park, Young-Sue;Lim, Muteak;Shin, Young-Hong
    • Geophysics and Geophysical Exploration
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    • v.16 no.2
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    • pp.91-96
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    • 2013
  • This study proposes a method to correct inclination of instrument during exploration with a biaxial clinometer and GNSS compass. In 3-component magnetometry, measured vectors are ordinarily described in randomly inclined observation coordinate system due to movement, vibration, and shaking of instrument. Therefore, rotation angles of observation plane are needed to transform it into geodetic coordinate system. In this study, we measured inclination angles of observation plane by using 2-axis clinometer and GNSS compass, and derived proper parameters for rotational transform from them. We applied the conversion method to on-board 3-component magnetometry, and then transformed raw data into proper values on geodetic coordinate system.

Comparative Study on Physical and Mechanical Characteristics of Volcanic Rocks in Jeju Island (제주도 화산암의 물리・역학적 특성에 대한 비교연구)

  • Yang, Soon-Bo
    • Journal of the Korean Geotechnical Society
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    • v.30 no.11
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    • pp.39-49
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    • 2014
  • Volcanic rocks in Jeju island show vesicular structure caused by various environmental factors, and indicate the differences in geological and mechanical characteristics from region to region. Previous studies on the volcanic rocks in Jeju island have been actively conducted on geological and chemical properties in terms of geophysics and geology and on physical and mechanical properties in terms of engineering. But comprehensive comparative analysis on physical and mechanical properties of volcanic rocks in Jeju island is not conducted. In this study, the physical and mechanical properties of volcanic rocks in Jeju island were compared and analyzed comprehensively through the existing research papers and reports about volcanic rocks in Jeju island. As a result, it was found that the relationship between absorption (porosity) and apparent specific gravity is commonly linear and could be represented as two different linear approximations. In addition, it was found that the relationship between P-wave velocity and S-wave velocity and the relationship between absorption (porosity) and uniaxial compressive strength could be classified more clearly, considering two different linear relationships in absorption (porosity) and apparent specific gravity.

A Pole-pole Electrical Survey for Groundwater (2극법 전기비저항 탐사에 의한 지하수탐사)

  • Cho Dong-heng;Jee Sang-keun
    • Geophysics and Geophysical Exploration
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    • v.3 no.3
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    • pp.88-93
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    • 2000
  • The present study may be summarized as follows. By means of a pole-pole electrical survey, major geological features, i.e, fresh rocks, fractured & weak & saturated rocks, fresh water bearing aquifer, were successfully delineated in the surveyed area of a granite region in Korea. The subsequent Schlumberger sounding and drilling confirmed the existence of the acquifer at 60 m depth as expected. But one more minor acquifer which does not show up in the resistivity depth section was met at 100 m depth. A simple forward modelling leads the authors to believe that any other electrode configuration, e.g., Wenner, Schlumberger, dipole-dipole, pole-dipole, would not detect the deeper aquifer. Under these circumstances, further studies remain to be done in connection with the spatial resolution in the vertical direction.

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Applicability of Geophyscal Well Logging in the Assessment of Seawater Intrusion (임해지역 해수침투 평가를 위한 물리검층의 적용성)

  • Lee Sang-Gyu;Hwang Sae-Ho;Hwang Hak-Su;Park In-Hwa
    • Geophysics and Geophysical Exploration
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    • v.3 no.3
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    • pp.101-111
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    • 2000
  • In order to assess the seawater intrusion, induction, temperature and conductivity of fluid, and natural gamma logs were obtained in nine wells at the three study areas having different hydrogeologic characteristics. Besides surface geophysical exploration, supplementary geophysical well logs were carried out to understand the hydrogeological characteristics related to the seawater intrusion in the study areas. The geophysical well logs have been proved to increase the accuracy of interpretation of the surface geophyscial exploration's data for assessment of seawater intrusion, and to get the optimum depth for a long monitoring of groundwater. They, also, revealed that the identification of hydrogeological units for strata's porosity was able to be achieved and were illustrated the applicability of geophysical well logs monitoring. Finally, geophysical well logs are expected to play to get the more quantitative information of seawater infusion, if it is fully collaborated with a better method that is strata's resistivity determination with not relatively much effected by seawater within the drilled borehole and that is the porosity measurement with built on small diameter PVC casing.

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3-D Crosshole EM Modeling by the Extended Born Approximations (확장된 Born근사법에 의한 시추공간 3차원 전자탐사 모델링)

  • Cho, In-Ky;Choi, Kyoung-Hwa
    • Geophysics and Geophysical Exploration
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    • v.2 no.3
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    • pp.142-148
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    • 1999
  • Three-dimensional electromagnetic modeling algorithm in homogeneous half-space was developed using the extended Born approximation to an electric field integral equation. To examine the performance of the extended Born approximation algorithm, the results were compared with those of the full integral equation results. For a crosshole source-receiver configuration, the agreement between the integral equation and the extended Born approximation was remarkable when the source frequency is lower than 20 kHz and conductivity contrast lower than 1:10. Beyond this conductivity contrast, the simulated results by the extended Born approximation exhibit a difference with respect to those by the integral equation. Therefore, the limit of accuracy lies below contrast of 1:10 in the extended Born approximation. Since for the source frequency range from 20 kHz to 100 kHz, however, the difference is relatively small, the extended Born approximation could be used for a reasonable 3-D EM modeling algorithm.

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3-Dimensional Sequence Interpretation of Seismic Attributes in the Structurally Complex Area (복잡한 지질구조 지역에서의 3차원 탄성파 Attribute를 이용한 층서해석 사례)

  • Kim, Kun-Deuk
    • Geophysics and Geophysical Exploration
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    • v.2 no.3
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    • pp.149-153
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    • 1999
  • The study was performed as a part of 3-D exploration project of the South Con Son basin, where Korea National Oil Co. (KNOC) and SHELL Company are performing joint operation. In the structurally complex area, seismic facies or lap-out patterns, which are usually the tools for the conventional seismic stratigraphy developed by Exxon Group (Vail et at., 1977), are not easily identifiable. Therefore, stratigraphic informations are mainly extracted from seismic attribute maps of each sequence or systems tracts, and isopach maps in correlation with the stratigraphic information from the wells. The attribute maps of the sequence or systems tract boundaries and isopach map describe the variations of paleodepositional environments. The shape of the attribute maps of the boundaries is a reasonable description of the shape of the paleodepositional surface. With other maps such as isopach and structural maps, the variations of the parasequences in the systems tracts can be projected using the surface attribute maps. The reflection intensity attribute at each sequence or system tract boundary can be related to lithology, facies or porosity distributions. The azimuth attribute of source rock sequence can be used to identify the hydrocarbon migration patterns into the prospects. The overall risks of reservoir rocks, cap rocks, structure and hydrocarbon migrations were computed using the results of the study.

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Improvement of Reverse-time Migration using Modified Receiver Aperture (수진기 배열 변경에 의한 역시간 구조보정 영상 개선 연구)

  • Cheong Soon-Hong;Shin Chang-Soo
    • Geophysics and Geophysical Exploration
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    • v.6 no.3
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    • pp.153-159
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    • 2003
  • Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

Derivation the Correction of the Component of the Recorder and the Application of Hilbert Transformation to Calculating the Frequency Response of the Sensor (지진기록계 보정과 힐버트 변환 적용에 의한 센서 주파수 응답 계산)

  • Cho, Chang Soo
    • Geophysics and Geophysical Exploration
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    • v.19 no.2
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    • pp.84-90
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    • 2016
  • The validation of performance test for newly developed or old-used sensor is very important in the earthquake monitoring and seismology using earthquake data. Especially the frequency response of the sensor is mainly used to correct the earthquake data. The technique of the calculation of phase and amplitude with Hilbert transformation for earthquake data that is filtered with band limited frequency in time domain is applied to calculate the frequency response of the sensor. This technique was tested for the acceleration sensors, CMG-5T of 1g and 2g installed on the vibration table at the laboratory and we could obtain satisfactory result. Tohoku large earthquake in 2011 observed at the station SNU that has accelerometer, ES-T and seismometer, STS-2 operated by KIGAM was also used to test the field data applicability. We could successfully get the low frequency response of broad band sensor, STS-2. The technique by using band limited frequency filter and Hilbert transformation showed the superior frequency response to the frequency spectrum ratio method for noisy part in data.

Relationship Analysis of Volumetric Water Content According to the Dielectric Constant for Stability Analysis of Ground Excavation (굴착의 안정성에 미치는 영향인자 분석을 위한 전자기적 유전상수와 체적함수비와의 상관관계 분석기법 연구)

  • Han, Yushik;Sohn, Hee Jeung;Yoo, Ki Cheong
    • Geophysics and Geophysical Exploration
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    • v.19 no.3
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    • pp.153-163
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    • 2016
  • In order to prevent ground collapses by groundwater level drawdown, we need to understand the groundwater flow and also make an analytical approach to the cause of the collapses. In this study, we used the result of the soil lab tests to compare and review the suitability of the various interaction equations about the relation between volumetric water content and the dielectric constant. In addition, using GPR (Ground-Penetrating Radar), we reviewed the possibility of calculating an estimate of dielectric constant. Lastly, we applied seepage analysis and stress-strain analysis to the sandy ground given by ground excavation. In comparison with the previous result of the soil lab tests, we similarly predicted the suction of unsaturated soil from results of stress-strain analysis considered the seepage force for the unsaturated soil.

Location of Recent Micro-earthquakes in the Gyeongju Area (최근 경주지역 미소지진 진원 위치)

  • Han, Minhui;Kim, Kwang-Hee;Son, Moon;Kang, Su Young;Park, Jung-Ho
    • Geophysics and Geophysical Exploration
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    • v.19 no.2
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    • pp.97-104
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    • 2016
  • Small to large earthquakes have been reported in Gyeongju and its vicinity in southeast Korea during historical period as well as instrumental observation period. We identified and located more than 300 earthquakes that occurred between January 2010 and December 2014 in a $20km{\times}30km$ area, but were unreported because of their small magnitudes. We used the Joint Hypocenter Determination (JHD) method to minimize the influence of the differences between the actual earth structure and 1-D velocity model for earthquake locations. The potential relationship between the previously reported Quaternary faults and the earthquake hypocenters was investigated. Many micro-earthquakes were found to be located in the southern segment of the Yeonil Tectonic Line, the Seokup fault, and the Waup basin boundary faults.