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Econ. Environ. Geol. 2021; 54(6): 743-752

Published online December 28, 2021

https://doi.org/10.9719/EEG.2021.54.6.743

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Expected Segmentation of the Chugaryung Fault System Estimated by the Gravity Field Interpretation

Sungchan Choi1, Eun-Kyeong Choi1,*, Sung-Wook Kim1, Young-Cheol Lee2

1Geo-information Institute, GI Co. Ltd., Busan 47598, Korea
2Institute of Geologic Hazard & Industrial Resources, Pusan National University, Busan 46241, Korea

Correspondence to : *choiek@naver.com

Received: October 20, 2021; Revised: November 28, 2021; Accepted: December 21, 2021

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The three-dimensional distribution of the fault was evaluated using gravity field interpretation such as curvature analysis and Euler deconvolution in the Seoul-Gyeonggi region where the Chugaryeong fault zone was developed. In addition, earthquakes that occurred after 2000 and the location of faults were compared. In Bouguer anomaly of Chugaryeong faults, the Pocheon Fault is an approximately 100 km fault that is extended from the northern part of Gyeonggi Province to the west coast through the central part of Seoul. Considering the frequency of epicenters is high, there is a possibility of an active fault. The Wangsukcheon Fault is divided into the northeast and southwest parts of Seoul, but it shows that the fault is connected underground in the bouguer anomaly. The magnitude 3.0 earthquake that occurred in Siheung city in 2010 occurred in an anticipated fault (aF) that developed in the north-south direction. In the western region of the Dongducheon Fault (≒5,500 m), the density boundary of the rock mass is deeper than that in the eastern region (≒4,000 m), suggesting that the tectonic movements of the western and eastern regions of the Dongducheon Fault is different. The maximum depth of the fracture zone developed in the Dongducheon Fault is about 6,500 m, and it is the deepest in the research area. It is estimated that the fracture zone extends to a depth of about 6,000 m for the Pocheon Fault, about 5,000 m for the Wangsukcheon Fault, and about 6,000 m for the Gyeonggang Fault.

Keywords gravity field interpretation, curvature analysis, Pocheon fault, Wangsukcheon fault, Dongducjeon fault

추가령단층대의 중력장 데이터 해석

최승찬1 · 최은경1,* · 김성욱1 · 이영철2

1지아이 지반정보연구소
2부산대학교 지질재해·산업자원연구소

요 약

추가령 단층대가 발달하는 서울-경기 지역에서 단층의 3차원적인 규모를 확인하기 위해서, 곡률 분석(Curvature analysis)과 오일러 디콘볼루션(Euler deconvolution) 등의 중력장 해석 방법을 이용하여 잔여 중력이상을 해석하였다. 또한 2000년 이후 발생한 진앙과 비교하여 단열 특성을 비교하였다. 부게이상에서 포천단층은 경기 북부에서 서울의 중심부를 지나서 서해안 지역까지 연결된 약 100 km 단층으로 진앙이 빈도가 높아 활성 단층의 가능성이 있고, 단층을 경계로 동서 방향으로 7 km 정도의 변위가 관찰된다. 왕숙천단층은 서울을 중심으로 북동부와 서남부로 분절되어 있으나 지하에서 연결을 암시하는 단층 분절로 추정되는 중력이상대가 관찰된다. 특히 2010년 시흥에서 발생한 규모 3.0의 지진은 남북 방향으로 발달하는 20 km 길이의 단층에 의한 것으로 판단된다. 동두천단층의 서쪽 지역(≒5,500 m)은 중력경계면이 동쪽 지역(≒4,000 m)보다 깊게 나타나며 이는 동두천단층을 중심으로 서쪽 지역과 동쪽 지역의 지구조적인 운동이 다르다는 것을 시사한다. 동두천단층에서 발달한 파쇄대의 최대 깊이는 약 6,500 m이며 연구 지역에서는 가장 깊다. 포천 단층은 약 6,000 m, 왕숙천 단층은 약 5,000 m, 경강 단층은 약 6,000 m 깊이까지 파쇄대가 연장되는 것으로 판단된다.

주요어 중력장 해석, 곡률 분석, 포천단층, 왕숙천단층, 동두천단층

Article

Research Paper

Econ. Environ. Geol. 2021; 54(6): 743-752

Published online December 28, 2021 https://doi.org/10.9719/EEG.2021.54.6.743

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Expected Segmentation of the Chugaryung Fault System Estimated by the Gravity Field Interpretation

Sungchan Choi1, Eun-Kyeong Choi1,*, Sung-Wook Kim1, Young-Cheol Lee2

1Geo-information Institute, GI Co. Ltd., Busan 47598, Korea
2Institute of Geologic Hazard & Industrial Resources, Pusan National University, Busan 46241, Korea

Correspondence to:*choiek@naver.com

Received: October 20, 2021; Revised: November 28, 2021; Accepted: December 21, 2021

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The three-dimensional distribution of the fault was evaluated using gravity field interpretation such as curvature analysis and Euler deconvolution in the Seoul-Gyeonggi region where the Chugaryeong fault zone was developed. In addition, earthquakes that occurred after 2000 and the location of faults were compared. In Bouguer anomaly of Chugaryeong faults, the Pocheon Fault is an approximately 100 km fault that is extended from the northern part of Gyeonggi Province to the west coast through the central part of Seoul. Considering the frequency of epicenters is high, there is a possibility of an active fault. The Wangsukcheon Fault is divided into the northeast and southwest parts of Seoul, but it shows that the fault is connected underground in the bouguer anomaly. The magnitude 3.0 earthquake that occurred in Siheung city in 2010 occurred in an anticipated fault (aF) that developed in the north-south direction. In the western region of the Dongducheon Fault (≒5,500 m), the density boundary of the rock mass is deeper than that in the eastern region (≒4,000 m), suggesting that the tectonic movements of the western and eastern regions of the Dongducheon Fault is different. The maximum depth of the fracture zone developed in the Dongducheon Fault is about 6,500 m, and it is the deepest in the research area. It is estimated that the fracture zone extends to a depth of about 6,000 m for the Pocheon Fault, about 5,000 m for the Wangsukcheon Fault, and about 6,000 m for the Gyeonggang Fault.

Keywords gravity field interpretation, curvature analysis, Pocheon fault, Wangsukcheon fault, Dongducjeon fault

추가령단층대의 중력장 데이터 해석

최승찬1 · 최은경1,* · 김성욱1 · 이영철2

1지아이 지반정보연구소
2부산대학교 지질재해·산업자원연구소

Received: October 20, 2021; Revised: November 28, 2021; Accepted: December 21, 2021

요 약

추가령 단층대가 발달하는 서울-경기 지역에서 단층의 3차원적인 규모를 확인하기 위해서, 곡률 분석(Curvature analysis)과 오일러 디콘볼루션(Euler deconvolution) 등의 중력장 해석 방법을 이용하여 잔여 중력이상을 해석하였다. 또한 2000년 이후 발생한 진앙과 비교하여 단열 특성을 비교하였다. 부게이상에서 포천단층은 경기 북부에서 서울의 중심부를 지나서 서해안 지역까지 연결된 약 100 km 단층으로 진앙이 빈도가 높아 활성 단층의 가능성이 있고, 단층을 경계로 동서 방향으로 7 km 정도의 변위가 관찰된다. 왕숙천단층은 서울을 중심으로 북동부와 서남부로 분절되어 있으나 지하에서 연결을 암시하는 단층 분절로 추정되는 중력이상대가 관찰된다. 특히 2010년 시흥에서 발생한 규모 3.0의 지진은 남북 방향으로 발달하는 20 km 길이의 단층에 의한 것으로 판단된다. 동두천단층의 서쪽 지역(≒5,500 m)은 중력경계면이 동쪽 지역(≒4,000 m)보다 깊게 나타나며 이는 동두천단층을 중심으로 서쪽 지역과 동쪽 지역의 지구조적인 운동이 다르다는 것을 시사한다. 동두천단층에서 발달한 파쇄대의 최대 깊이는 약 6,500 m이며 연구 지역에서는 가장 깊다. 포천 단층은 약 6,000 m, 왕숙천 단층은 약 5,000 m, 경강 단층은 약 6,000 m 깊이까지 파쇄대가 연장되는 것으로 판단된다.

주요어 중력장 해석, 곡률 분석, 포천단층, 왕숙천단층, 동두천단층

    Fig 1.

    Figure 1.(A) Study area (green solid rectangle) locates in the western part of the Gyeonggi Massif, middle part of the Korean peninsula. CFS: Chugaryung Fault System, YSF: Yangsan Fault, GY: Gyeongju earthquake, PO: Pohang earthquake. (B) The NNE-SSW directing Chugaryung Fault System (CFS in A) is composed of several fault lines numbered by 1 ~ 7. Gravity stations in the study area were about 5,000 points, which are indicated by green dots. (C) The Annual frequency of earthquake registered in the study area shows a clear difference before and after the Gyeongju earthquake (black rectangle). The annual earthquake frequency after the Gyeongju earthquake increased rapidly to more than 4 times.
    Economic and Environmental Geology 2021; 54: 743-752https://doi.org/10.9719/EEG.2021.54.6.743

    Fig 2.

    Figure 2.The geological map of the study area shows that the Chugaryung fault system is mainly covered by Precambrian Gneiss, Jurassic Granites and Cretaceous volcanics. About 100 density measurements of igneous, metamorphic, and volcanic rocks are indicated by symbols that relate to the observed values (Park et al., 2009). The mean densities of the Granites, Volcanics and Gneiss are measured of 2.60, 2.56 and 2.67 g/cm3, respectively. ① –⑦ : Fault lines (see Fig. 2 for the identifications).
    Economic and Environmental Geology 2021; 54: 743-752https://doi.org/10.9719/EEG.2021.54.6.743

    Fig 3.

    Figure 3.The complete Bouguer anomaly map (A) over the research area has a mean value of approximately –5.0 mGal and a range from –25.0 to 20.0 mGal. The higher Bouguer gravity anomalies relative to the mean value (–5.0 mGal) are generally observed to the west along the coast. The anomalies lower than the mean value (–5 mGal) reveal along the Chugaryoung fault system, where the Jurrasic Grantite are mainly exposed. ① – ⑦ : Fault lines (see Fig. 2 for the identifications). (B) The regional gravity anomalies are calculated using a wavelength of 20 km.
    Economic and Environmental Geology 2021; 54: 743-752https://doi.org/10.9719/EEG.2021.54.6.743

    Fig 4.

    Figure 4.A residual anomaly map of the research area (A), which is calculated by subtracting the regional gravity field (Fig. 3B) from the Bouguer gravity field (Fig. 3A). The residual anomalies reflect the gravity effects of the crustal rocks much better than Bouguer anomalies (Fig. 3A). The dip curvature map (B) shows anticipated fault lines with a NE-SW direction (red dotted lines with aF2, aF5, aF8 and aF9) and a N-S direction (red dotted lines with aF1, aF3, aF4 and aF6). ① − ⑦ : Fault (see Fig. 2 for the identifications).
    Economic and Environmental Geology 2021; 54: 743-752https://doi.org/10.9719/EEG.2021.54.6.743

    Fig 5.

    Figure 5.(A) Euler deconvolution technique are applied by using the residual gravity- (Fig. 4A) to obtain preliminary information on the 3D distribution of source points in the study area. The deep mass points greater than the mean depth (4,500 m), are mainly clustered in the western parts of the Dongducheon fault line marked with ①, while the eastern part of the Pocheon fault marked with ② is expected to be less than 4,000 m deep. Residual anomalies along the W-E profile (B) (refer to Fig. A for the location of the profile) ranges from –2.0 mGal to 6.0 mGal. The maximum source depth along the profile (D) are compared to the rock types (C).
    Economic and Environmental Geology 2021; 54: 743-752https://doi.org/10.9719/EEG.2021.54.6.743
    KSEEG
    Apr 30, 2024 Vol.57 No.2, pp. 107~280

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