Geomorphology of a mass failure zone and their implication on the submarine slope stability in the northwestern part of the East Sea (Japan Sea), Korea
Presented by Dr. Seong-Pil KIM on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Track: Poster presentations
Topographic and geologic features of a mass failure zone were investigated in the mid-eastern continental margin of the Korean peninsula. The surveyed area resides on a gentle (less than 2 degree) continental slope running down to a submarine plateau in the northwestern part of the Ulleung Basin. The Ulleung Basin is a back-arc basin which was opened during the Tertiary Period behind the Japanese islands. High-resolution echo-sounders, a 3.5-kHz acoustic profiler and a meter-scale sediment corer were used for onboard data acquisition, which was followed by laboratory data processing and sediment analyses. Based on the study results a well-preserved slope failure scar could be delineated and examined in detail. The overall shape of the slope scar is tongue-like and comprised of at least two superimposed scars. Each of the scars runs more than ten kilometers downward toward the top of the Kangwon Plateau (the eastern part of the Korea Plateau) covering more than 20 km2 of aerial extent. In the along-scar sections the headwalls could clearly be defined with abrupt depth changes and shallow subsurface acoustic reflectors. The internal surfaces of the scars are generally flat and show similar slope angle down to about 1,000-m depth contour. Further below the 1,000-m contour the surfaces change their shapes into hummocky mounds with deformed and irregular acoustic reflectors implying the existence of mass-transported sediment deposit. In the cross-scar sections stepped seafloor could clearly be noticed, which indicates the overall shape of the scar zone is a cumulative result of recursive failure events. According to the textural and geotechnical properties of the cored samples the sediments in the failure zone are clay-rich, highly plastic and shear-resistant, which is not in favor of mass wasting. Considering the earthquake records around the Korean peninsula the mass failures in the study area imply the tectonic condition.