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The First Discovery of Quaternary Fault in the Western Part of the South Yangsan Fault - Sinwoo Site

양산단층 남부 이서 지역에서 최초로 발견된 제4기 단층 - 신우지점

  • Choi, Sung-Ja (Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Ghim, Yong Sik (Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Cheon, Youngbeom (Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Ko, Kyoungtae (Geology Division, Korea Institute of Geoscience and Mineral Resources)
  • 최성자 (한국지질자원연구원 국토지질연구본부) ;
  • 김용식 (한국지질자원연구원 국토지질연구본부) ;
  • 천영범 (한국지질자원연구원 국토지질연구본부) ;
  • 고경태 (한국지질자원연구원 국토지질연구본부)
  • Received : 2019.06.10
  • Accepted : 2019.06.26
  • Published : 2019.06.28

Abstract

During the detailed geological survey around the southern Yangsan Fault, we newly found a Quaternary fault outcrop, which cuts unconsolidated sediments. The fault named the Sinwoo site, located in the Sinwoo pasture, Miho-ri, Duseo-myeon, Ulsan metropolitan city, is the first discovered Quaternary fault near the western part of the south Yangsan Fault. In this study, we provide information on characteristics of fault geometry and unconsolidated sediment at Sinwoo site based on the analysis data of topography, drainage, and lineament around the study site. The fault site is situated at pediment slope, but fan-shaped middle terrace, as well as thick sediment exposed at low terrace, indicates that the unconsolidated sediments have been deposited in the alluvial fan environment. The drainage develops to the third-order drainage system, and the first and the second drainage system meet at right angles to each other and form a radial drainage pattern. In addition, the NE-SW direction lineaments can be identified on the basis of the curvature of the river and the step of the topographic relief, running over the Sinwoo site. The fault of $N30-35^{\circ}E/79-82^{\circ}SE$ shows ~ 5.8 m apparent vertical offset and dominantly reverse-slip sense based on slickenline, rotation of pebbles, and drag folding at footwall. However, some discontinuous sediments observed in the footwall are interpreted as fissure-filling materials due to the strike-slip movement. Now, we are under multidisciplinary investigations of additional field survey and age dating in order to determine the evolution of Sinwoo site fault during the Quaternary.

Keywords

Sinwoo site;quaternary fault;pediment;reverse-slip sense;strike-slip movement

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Fig. 1. Simplified regional geological map of the eastern part of the Gyeongsang basin with the location of the study area, modified after Chwae et al. (1995) and Son et al. (2015).

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Fig. 2. Geomorphological map around the Sinwoo site based on hillshade images from LiDAR-derived DEM and topographic profiles across the piedmont; a green circle:location of the fault; orange: higher surface; light green:middle surface; pink: lower surface; red dashed-lines:lineaments; blue lines: drainages; A-A’ and B-B’: topographic profile line.

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Fig. 3. A panoramic photograph of the Sinwoo site fault and unconsolidated sediment units.

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Fig. 4. Photographs of the detailed sedimentary facies.

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Fig. 5. Photographs of the detailed fault-related structures at the Sinwoo site fault.

Acknowledgement

Grant : (양산단층 중부지역) 위험요소 평가연구

Supported by : 한국연구재단

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