Near-surface geophysical studies in the Ulsan Fault Zone of Korea
Ki Young Kim 1 3 Dong Hoon Kim 2 So Young Lee 11 Department of Geophysics, Kangwon National University, Hyoja-Dong, Chuncheon, Kangwon-Do 200-701, Korea.
2 SEKOGEO Co. Ltd., Pyungchon-Dong, Angang, Gyeonggi-Do 431-070, Korea.
3 Corresponding author. Email: kykim@kangwon.ac.kr
Exploration Geophysics 39(1) 78-84 https://doi.org/10.1071/EG08008
Submitted: 22 November 2007 Published: 5 March 2008
Abstract
Recent earthquakes near nuclear power plants in Korea have triggered public concerns about possible seismicity of the Ulsan Fault Zone in the south-eastern part of the Korean peninsula. To reveal subsurface structures of this fault zone, we conducted high-resolution seismic refraction and reflection surveys, and closely spaced gravity measurements in the Dongchon River valley north of Ulsan, Korea. Here alluvium covers the north–south trending fault zone in a 1-km wide valley. Both source points and receivers were spaced at 5-m intervals for the 24-channel seismic refraction and reflection methods, along two profiles of 835 m and 415 m length. Gravity data were also measured along these profiles at 131 stations using a 10-m interval. Synergetic interpretation of seismic refraction, high-resolution seismic reflection, and gravity surveys across the valley indicates that the Ulsan Fault Zone was formed by apparent north–south strike-slip motions during the Cretaceous, and that some faults may have been reactivated by east–west compressional or transpressional stresses during the Tertiary or Quaternary.
Key words: Ulsan Fault, high-resolution seismic survey, refraction, reflection, gravity, reactivated.
Acknowledgments
This work was funded by the Korea Meteorological Research and Development Program under Grant CATER_2006–5201. This work was also supported by the Korea Power Engineering Co. (KOPEC) and the Institute of Research and Development for Earth Resources at Kangwon National University. We thank Mrs. Yeonjoong Kim and Hyeoncho Shin at KOPEC who provided useful information on the geology of the study area. We are also grateful to Professors Hee-Kwon Lee and Daekyo Cheong at Kangwon National University and Dr. Raymond M. René at Indiana University for their helpful discussions and suggestions during the progress of this work.
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