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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Geophysics and Geophysical Exploration
Journal Basic Information
Journal DOI :
Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 11, Issue 4 - Nov 2008
Volume 11, Issue 3 - Aug 2008
Volume 11, Issue 2 - May 2008
Volume 11, Issue 1 - Feb 2008
Selecting the target year
The Exploration Methodology of Seafloor Massive Sulfide Deposit by Use of Marine Geophysical Investigation
Kim, Hyun-Sub ; Jung, Mee-Sook ; Kim, Chang-Hwan ; Kim, Jong-Uk ; Lee, Kyeong-Yong ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 167~176
Lau basin of the south Pacific, as an active back arc basin, is promising area bearing seafloor massive hydrothermal deposit that is located in a subduction zone between the Pacific ocean plate and Indo-Australian continental plate. We performed multi-beam bathymetry survey in the Lau basin using EM120, to find out high hydrothermal activity Bone. Fonualei Rift and Spreading Center (FRSC) and Mangatolou Triple Junction (MTJ) area were selected for precise site survey through seafloor morphology investigation. The result of surface and deep-tow magnetometer survey showed that Central Anomaly Magnetization High (CAMH) recorded which is associated with active ridge in FRSC-2 and revealed very low magnetic anomalies that can be connected to past or present high hydrothermal activity in MTJ-1 seamount area. Moreover, the physical and chemical tracers of hydrothermal vent flume, i.e., transmission, hydrogen ion concentration (pH), adenosine triphosphate (ATP), methane (CH4) by use of CTD system, showed significant anomalies in those areas. From positive vent flume results, we could conclude that these areas were or are experiencing very active volcanic activities. The acquired chimney and hydrothermal altered bed rock samples gave us confidence of the existence of massive hydrothermal deposit. Even though not to use visual exploration equipment such as ROV, DTSSS, etc., traditional marine geophysical investigation approach might be a truly cost-effective tool for exploring seafloor hydrothermal massive deposit.
A Study of Waveform Inversion for Improvement of Sub-Salt Migration Image
Ha, Wan-Soo ; Pyun, Suk-Joon ; Son, Woo-Hyun ; Shin, Chang-Soo ; Ko, Seung-Won ; Seo, Young-Tak ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 177~183
The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.
Analysis of MT Data Acquired in Victoria, Australia
Lee, Seong-Kon ; Lee, Tae-Jong ; Uchida, Toshihiro ; Park, In-Hwa ; Song, Yoon-Ho ; Cull, Jim ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 184~196
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.
Seismic Imaging of a Tidal Flat: A Case Study for the Mineopo Area
Jou, Hyeong-Tae ; Kim, Han-Joon ; Lee, Gwang-Hoon ; Lee, Sang-Hoon ; Jung, Baek-Hoon ; Cho, Hyun-Moo ; Jang, Nam-Do ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 197~203
A shallow high-resolution seismic reflection survey was carried out at the Mineopo tidal flat on the western coast of Korea. The purpose of the survey was to investigate shallow sedimentary structure of the tidal flat associated with the recent sea level change. A total of 795 shots were generated at 1 m interval from a 5-kg hammer source and recorded on 48 channels of 100 Hz geophones along two mutually perpendicular profiles. The water-saturated ground condition resulted in suppressed ground rolls by significantly decreasing rigidity. In addition, seismic velocities over 1500 m/s provided easy segregation of reflected arrivals from lower velocity noise. As a consequence, seismic sections from the study area show significantly higher resolution and signal to noise ratio than conventional land seismic sections. The tidal flat consists of 5 sedimentary sequences above acoustic basement. The seismic sections reveal the continuous structure of the tidal flat formed in association with sea level rise during the Holocene.
Stability Analysis for the Pohang Deep Geothermal Borehole
Lee, Min-Jung ; Chang, Chan-Dong ; Lee, Jun-Bok ; Lee, Tae-Jong ; Hwang, Se-Ho ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 204~213
This paper presents the analysis about the stability of the Pohang deep geothermal borehole drilled in 2006. Severe wellhole instability problems such as collapse and tight hole occurred in weak rocks while drilling. Optimal mud pressure (mud window) required to prevent instability problems during drilling is obtained from analysis on in-situ stress and rock strength. The window is bounded by vertical stress in its upper limit and by either collapse pressure or pore pressure in its lower limit. Mud window varies with different types of rocks. In the top-most semi-consolidated mudstone formation, no mud window can secure borehole stability. In some weak rock types (basic dyke and crystal tuff), the borehole pressure needs to be higher by
than hydrostatic pressure. That means a mud density of 1.5 g/
or higher should be applied during drilling in order to prevent excessive collapse around the borehole.
Electrical Resistivity Response Due to the Variation of Embankment Shape and Reservoir Level
Oh, Seok-Hoon ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 214~220
The distortion effect of electrical response for two-dimensional (2-D) DC resistivity method was verified in terms of 2-D inversion result of synthetic data obtained by three-dimensional (3-D) modeling, which is frequently applied to assess the safety of center core-type fill dam structure. The distortion effect is due to 2-D interpretation for 3-D structure. By the modeling analysis, we found that the water level is correctly described in the resistivity section around the middle part rather than each end side of the embankment due to the 3-D terrain effect, when the material of the embankment is assumed as horizontally uniform. And when we set the slope of outer rock fill part as uniform. the sharper the slope of the center core is, the more similar the resistivity section reflects. On the other hand, when the slope of the rock fill is steep, the resistivity section shows the water level at lower position than the real one, and the 3-D distortion effect at the end side of the embankment was enhanced.
The Case Study on Application of 3 Dimensional Modeling Method with Geophysical Data
Heo, Seung ; Park, Joon-Young ; Do, Jung-Lok ; Yoo, In-Kol ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 221~229
The three dimensional model method is widely applied in resource development for feasibility study, mine design, excavation planning and process management by constructing the database of various data in 3 dimensional space. Most of geophysical surveys for the purpose of engineering and resource development are performed in 2 dimensional line survey due to the restriction of the field situation, technical or economical situation and so on. The acquired geophysical data are used as the input for the 2 dimensional inversion under the 2 dimensional assumption. But the geophysical data are affected by 3 dimensional space. Therefore in order to reduce the error caused by 2 dimensional assumption, the 2 dimensional inversion result must be interpreted considering the additional information such as 3 dimensional topography, geological structure, borehole survey etc. The applicability and usability of 3 dimensional modeling method are studied by reviewing the case study to the geophysical data acquired in field of engineering and resource development.
Characterization of S-velocity Structure Near Izmit City of Turkey Using Ambient Noise and MASW
Cho, Chang-Soo ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 230~241
Characteristics of transfer responses for arrays like triangle, hexagon and semicircle were investigated. To characterize the site near Izmit city with ambient noise measurement, dispersion curves of surface waves were derived with using array technique like F-K, High resolution F-K, MSPAC and H/V ratio was calculated. Also, MASW was surveyed to get the high frequency part of dispersion curves. The transition from fundamental mode to first high mode of surface waves for dispersion curve was observed. Dispersion curve of fundamental mode of ambient noise and first higher mode of MASW was used in inversion to get S-wave velocity structure of subsurface. None-unique problem of results of surface wave inversion was solved with comparison of result of refraction tomography performed with first arrivals of MASW data.
Study on the Limitation of AVO Responses Shown in the Seismic Data from East-sea Gas Reservoir
Shin, Seung-Il ; Byun, Joong-Moo ; Choi, Hyung-Wook ; Kim, Kun-Deuk ; Ko, Seung-Won ; Seo, Young-Tak ; Cha, Young-Ho ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 242~249
Recently, AVO analysis has been widely used in oil exploration with seismic subsurface section as a direct indicator of the existence of the gas. In the case of the deep reservoirs like the gas reservoirs in the East-sea, it is often difficult to observe AVO responses in CMP gathers even though the bright spots are shown in the stacked section. Because the reservoir becomes more consolidated as its depth deepens, P-wave velocity does not decrease significantly when the pore fluid is replaced by the gas. Thus the difference in Poisson's ratio, which is a key factor for AVO response, between the reservoir and the layer above it does not increase significantly. In this study, we analyzed the effects of Poisson's ratio difference on AVO response with a variety of Poisson's ratios for the upper and lower layers. The results show that, as the difference in Poisson's ratio between the upper and lower layers decreases, the change in the reflection amplitude with incidence angle decreases and AVO responses become insignificant. To consider the limitation of AVO responses shown in the gas reservoir in East-sea, the velocity model was made by simulation Gorae V structure with seismic data and well logs. The results of comparing AVO responses observed from the synthetic data with theoretical AVO responses calculated by using material properties show that the amount of the change in reflection amplitude with increasing incident angle is very small when the difference in Poisson's ratio between the upper and lower layers is small. In addition, the characteristics of AVO responses were concealed by noise or amplitude distortion arisen during preprocessing. To overcome such limitations of AVO analysis of the data from deep reservoirs, we need to acquire precisely reflection amplltudes In data acquisition stage and use processing tools which preserve reflection amplitude in data processing stage.
A Study of Feasibility of Dipole-dipole Electric Method to Metallic Ore-deposit Exploration in Korea
Min, Dong-Joo ; Jung, Hyun-Key ; Park, Sam-Gyu ; Chon, Hyo-Taek ; Kwak, Na-Eun ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 250~262
In order to assess the feasibility of the dipole-dipole electric method to the investigation of metallic ore deposit, both field data simulation and inversion are carried out for several simplified ore deposit models. Our interest is in a vein-type model, because most of the ore deposits (more than 70%) exist in a vein type in Korea. Based on the fact that the width of the vein-type ore deposits ranges from tens of centimeters to 2m, we change the width and the material property of the vein, and we use 40m-electrode spacing for our test. For the vein-type model with too small width, the low resistivity zone is not detected, even though the resistivity of the vein amounts to 1/300 of that of the surrounding rock. Considering a wide electrode interval and cell size used in the inversion, it is natural that the size of the low resistivity zone is overestimated. We also perform field data simulation and inversion for a vein-type model with surrounding hydrothermal alteration zones, which is a typical structure in an epithermal ore deposits. In the model, the material properties are assumed on the basis of resistivity values directly observed in a mine originated from an epithermal ore deposits. From this simulation, we can also note that the high resistivity value of the vein does not affect the results when the width of the vein is narrow. This indicates that our main target should be surrounding hydrothermal alteration zones rather than veins in field survey. From these results, we can summarize that when the vein is placed at the deep part and the difference of resistivity values between the vein and the surrounding rock is not large enough, we cannot detect low resistivity zone and interpret the subsurface structures incorrectly using the electric method performed at the surface. Although this work is a little simple, it can be used as references for field survey design and field data Interpretation. If we perform field data simulation and inversion for a number of models and provide some references, they will be helpful in real field survey and interpretation.
Gas Hydrate Exploration Using LWD/MWD in the Ulleung Basin, the East Sea of Korea
Kim, Gil-Young ; Yoo, Dong-Geun ; Kim, Won-Sik ; Lee, Ho-Young ; Park, Keun-Pil ;
Geophysics and Geophysical Exploration, volume 11, issue 3, 2008, Pages 263~270
The Gas Hydrate Research and Development Organization (KGHDO) of Korea accomplished successfully geophysical logging (LWD: Logging While Drilling, MWD: Measurement While Drilling) for five sites in 2007, in order to investigate the presence of gas hydrate in the Ulleung Basin, the East Sea of Korea. The togging parameters acquired from LWD/MWD dre electrical resistivity, acoustic velocity, neutron density and porosity, and natural gamma. In addition, pressure, temperature, and diameter of borehole were measured. LWD/MWD data showed several evidences indicating the presence of gas hydrate. Based on LWD/MWD data, three coring sites were selected for sampling of gas hydrate. Subsequently, various gas hydrate samples were collected directly from three sites. Therefore. the presence of gas hydrates was verified by coring. LWD/MWD data will be significantly used to estimate the amount of gas hydrate. Also, they will provide important information to elucidate about sedimentologic characteristics of gas-hydrate bearing formation and sedimentary environment of the Ulleung Basin.