• Title/Summary/Keyword: gravity interpretation

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Displacement of Dongducheon and Wangsukcheon Fault Observed by Gravity Field Interpretation (중력장 해석으로 관측된 동두천 및 왕숙천 단층의 변위)

  • Sungchan Choi;Sung-Wook Kim;Eun-Kyeong Choi;Younghong Shin
    • Economic and Environmental Geology
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    • v.57 no.1
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    • pp.73-81
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    • 2024
  • To estimate the tectonic displacement of the Chugaryeong Fault System (CFS), gravity surveys were conducted along the Dongducheon fault (DF) and the Wangsukcheon fault (WF). A total of 1,100 stations for the DF and WF regions have been added to the current gravity database. The results of the gravity interpretation indicate that (1) the dextral displacement of the DF is about 3,000 m, similar to the tectonic displacement (2,900-3,100 m) shown in the geological map. (2) The dextral displacement of the WF is about 3,200 m. (3) Taken together, the tectonic displacement of the CFS is estimated to be about 3,000 m on average. To investigate more accurate tectonic displacement of the CFS, further gravity surveys is planned for the Pocheon fault, Gyeonggang fault, and Inje fault.

A Study on the Generation of Capillary Waves on Steep Gravity Waves

  • Lee, Seung-Joon
    • Journal of Ship and Ocean Technology
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    • v.4 no.4
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    • pp.45-55
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    • 2000
  • A formal solution method using the complex analysis is given for the problems derived by Longuet-Higgins(1963). The same method is applied to a new perturbation problem of higher approximation. Interpretation of its solution made it possible to confirm that the rough agree-ment of Longuet-Higgins\`s prediction with experimental data of Cox(1958) was mainly due to the fact that the gravity effect in the perturbation problem was neglected for the case when the basic gravity wave not sufficiently steep.

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Gravity Field Interpretation and Underground Structure Modelling as a Method of Setting Horizontal and Vertical Zoning of a Active Fault Core (활성단층의 3차원적인 규모를 결정하기 위한 중력장 데이터의 해석 및 지각구조 모델링: 양산단층에서의 예)

  • Choi, Sungchan;Kim, Sung-Wook;Choi, Eun-Kyeong;Lee, Young-Cheol;Ha, Sangmin
    • Economic and Environmental Geology
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    • v.54 no.1
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    • pp.91-103
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    • 2021
  • In order to estimate the vertical and horizontal structural in the Yangsan fault core line (Naengsuri area, Pohang), we carried out gravity field measurements and interpretation procedures such as Euler deconvolution method and curvature analysis in addition to the forward modelling technique (i.e. IGMAS+). We found a prominent gravity difference of more than 1.5 mGal across the fault core. This indicates a distinct density difference between the western and eastern crustal area across the Yangsan fault line. Comparing this gravity field interpretation with other existent geologic and geophysical survey data (e.g. LiDAR, trenching, electric resistivity measurements), It is concluded that (1) the prominent gravity difference is caused by the density difference of about 0.1 g/㎤ between the Bulguksa Granite in the west and the Cretaceous Sandstone in the east side, (2) the fault core is elongated vertically into a depth of about 2,000 meters and extended horizontally 3,000 meters to the NNE direction from Naengsuri area. Our results present that the gravity field method is a very effective tool to estimate a three -dimensional image of the active fault core.

Gravity and Magnetic Surverys for Volcanic Rocks in Yeoncheon Area, kyonggi-do (경기도 인천지역 분포하는 화산암류에 대한 중력 및 자력 탐사 연구)

  • 박혁진
    • Economic and Environmental Geology
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    • v.32 no.6
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    • pp.645-651
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    • 1999
  • The gravity and magnetic measurements have been obtained from 34 stations with 50m intervals along the survey line positioned between Jangtanri and sindapri for studying subsurface geology and structures of the volcanic rocks in Yeoncheon area. The Bouguer gravity and magnetic anomaly values were evaluated from the reduction of the field observation, and then interpreted by Nettleton's method and maximum-pepth rules, are approximately 160m based on magnetic data and 135m based on gravity data. High Bouguer gravity anomaly zone between 0m in Jangtanri and 900m along the survery line, is caused by thick and high density, older dasalt which is positioned beneath jijangbong tuff breccia, and this result corresponds to the interpretation result based on magnetic anomly. Lower gravity and magnetic anomaly zones ariund 900m are caused by between 1300m and 1550m are caused by high density of Quarternary basalt exposed in the surface, and lower gravity and magnetic anomalies at 200m and 1250m are caused by faults.

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Evaluation of Soil Compaction Using Gravity Field Interpretation and UAV-based Remote Sensing Information (중력 데이터 해석과 드론원격정보를 이용한 지반의 다짐도 평가)

  • Kim, Sung-Wook;Choi, Sungchan;Choi, Eun-Kyoung;Lee, Yeong-Jae;Go, Daehong;Lee, Kyu-Hwan
    • The Journal of Engineering Geology
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    • v.31 no.3
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    • pp.283-293
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    • 2021
  • The homogeneity of the compacted ground was analyzed using drone-based remote terrain and gravity field data. Among the topographic elements calculated by the hydrological algorithm, the topographic curvature effectively showed the shape of the surface that occurred during the compaction process, and the non-uniformly compacted area could be identified. The appropriate resolution of the digital topography requires a precision of about 10 cm. Gravity field Interpretation was performed to analyze the spatial density change of the compacted ground. In the distribution of residual bouguer gravity anomaly, the non-homogeneously compacted area showed a different magnitude of gravity than the surrounding area, and the difference in compaction was identified through gravity-density modeling. From the results, it is expected that the topographic element and gravitational field analysis method can be used to evaluate the homogeneity of the compacted ground.

Spatial distribution of hydrocarbon reservoirs in the West Korea Bay Basin in the northern part of the Yellow Sea, estimated by 3D gravity forward modeling (3차원 중력 모델링에 의해 예측된 황해 북부 서한만 분지 석유 저류층의 공간적 분포)

  • Choi, Sungchan;Ryu, In-Chang
    • Journal of the Geological Society of Korea
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    • v.54 no.6
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    • pp.641-656
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    • 2018
  • Although an amount of hydrocarbon has been discovered in the West Korea Bay Basin (WKBB), located in the North Korean offshore area, geophysical investigations associated with these hydrocarbon reservoirs are not permitted because of the current geopolitical situation. Interpretation of satellite derived potential field data can be alternatively used to image three-dimensional (3D) density distribution in the sedimentary basin associated with hydrocarbon deposits. We interpreted the TRIDENT satellite-derived gravity field data to provide detailed insights into the spatial distribution of sedimentary density structures in the WKBB. We used 3D forward density modeling for the interpretation that incorporated constraints from existing geological and geophysical information. The gravity data interpretation and 3D forward modeling showed that there are two modeled areas in the central subbasin that are characterized by very low density structures, with a maximum density of about $2,000kg/m^3$, indicating some type of hydrocarbon reservoir. One of the anticipated hydrocarbon reservoirs is located in the southern part of the central subbasin with a volume of about $250km^3$ at a depth of about 3,000 m in the Cretaceous/Jurassic layer. The other hydrocarbon reservoir should exist in the northern part of the central subbasin, with an average volume of about $300km^3$ at a depth of about 2,500 m. A comparison between the TRIDENT derived gravity field and the ship-based gravity field measured in 1980s shows us that our results are highly reliable and there is a very high probability to detect another low-density layer existings in the northwestern part of the central subbasin.

A Study on Interpretation of Gravity Data by using Iterative Inversion Methods (반복적(反復的) 역산법(逆算法)에 의(依)한 중력자료(重力資料)의 해석(解析)에 관(關)한 연구(硏究))

  • Roh, Cheol-Hwan;Yang, Sung-Jin;Shin, Chang-Soo
    • Economic and Environmental Geology
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    • v.22 no.3
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    • pp.267-276
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    • 1989
  • This paper presents results of interpretaton of gravity data by iterative nonlinear inversion methods. The gravity data are obtained by a theoretical formula for two-dimensional 2-layer structure. Depths to the basement of the structure are determined from the gravity data by four interative inversion methods. The four inversion methods used here are the Gradient, Gauss-Newton, Newton-Raphson, and Full Newton methods. Inversions are performed by using different initial guesses of depth for the over-determined, even-determined, and under-determined cases. This study shows that the depth can be determined well by all of the methods and most efficiently by the Newton-Raphson method.

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Gravity Exploration Inferring the Source Granite of the NMC Moland Mine, Jecheon, Chungbuk (충북 제천 NMC 몰랜드 광산의 관계 화성암에 대한 중력탐사)

  • Shin, Young Hong;Yoo, Bong Chul;Lim, Mutaek;Park, Yeong-Sue;Ko, In Se
    • Economic and Environmental Geology
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    • v.47 no.2
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    • pp.107-119
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    • 2014
  • NMC Moland mine, which is classified as a contact replacement or skarn deposit, has been interpreted to have been formed by Daebo igneous activity which intruded into the Joseon Supergroup, because it is quite closely located to Jecheon granite. However, an alternative interpretation was recently suggested that the mine could be related with the hydrothermal fluid originated from Cretaceous granitic rocks, bringing about skarnization and Mo mineralization. Here we present an interpretation on the source granite of the mine based on the gravity exploration: the gravity anomaly, unlike the surface geology, shows that the Muamsa granite could be the related granite of the mine, because its hidden subsurface structure is expected to be more widely extended to surrounding area of the mine and deeper than the Jecheon granite.

A Study on Interpretation of Gravity Data on Two-Dimensional Geologic Structures by Iterative Nonlinear Inverse (반복적 비선형역산에 의한 2차원 지질구조의 중력자료 해석 연구)

  • Ko, Chin-Surk;Yang, Seung-Jin
    • Economic and Environmental Geology
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    • v.27 no.5
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    • pp.479-489
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    • 1994
  • In this paper, the iterative least-squares inversion method is used to determine shapes and density contrasts of 2-D structures from the gravity data. The 2-D structures are represented by their cross-sections of N-sided polygons with density contrasts which are constant or varying with depth. Gravity data are calculated by theoretical formulas for the above structure models. The data are considered as observed ones and used for inversions. The inversions are performed by the following processes: I) polygon's vertices and density contrast are initially assumed, 2) gravity are calculated for the assumed model and error between the true (observed) and calculated gravity are determined, 3) new vertices and density contrast are determined from the error by using the damped least-squares inversion method, and 4) final model is determined when the error is very small. Results of this study show that the shape and density contrast of each model are accurately determined when the density contrast is constant or vertical density gradient is known. In case where the density gradient is unknown, the inversion gives incorrect results. But the shape and density gradient of the model are determined when the surface density contrast is known.

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Microgravity for Engineering and Environmental Applications (토목.환경 응용을 위한 고정밀 중력탐사)

  • Park, Yeong-Sue;Rim, Hyoung-Rae;Lim, Mu-Taek
    • 한국지구물리탐사학회:학술대회논문집
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    • 2007.12a
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    • pp.15-25
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    • 2007
  • Gravity method could be one of the most effective tool for evaluating the soundness of basement which is directly correlated with density and its variations. Moreover, Gravimeter is easy to handle and strong to electromagnetic noises. But, gravity anomaly due to the target structures in engineering and environmemtal applications are too small to detect, comparing to the external changes, such as, elevation, topography, and regional geological variations. Gravity method targeting these kinds of small anomaly sources with high precision usually called microgravity. Microgravimetry with precision and accuracy of few ${\mu}Gal$, can be achieved by the recent high-resolution gravimeter, careful field acquisition, and sophisticated processing, analysis, and interpretation routines. This paper describes the application of the microgravity, such as, density structure of a rock fill dam, detection of abandoned mine-shaft, detection and mapping of karstic cavities in limestone terrains, and time-lapse gravity for grout monitoring. The case studies show how the gravity anomalies detect the location of the targets and reveal the geologic structure by mapping density distributions and their variations.

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