Evidence of Active Faulting and the Influences on Coastal Terrace Development along the Central East Coast of the Korean Peninsula

Choi K. H. and Yi. S., 2024. Evidence of active faulting and the influences on the coastal terrace development along the central east coast of the Korean Peninsula. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 768-772. Charlotte (North Carolina), ISSN 0749-0208. Coastal terraces along the east coast of the Korean Peninsula are considered evidence of either tectonic uplift or quaternary sea level fluctuations. The calculated uplift rate of the central east coast (c. 0.3∼0.4 m/ky) during the MIS-7 is significantly higher than the mean uplift rate of the east coast (c. 0.1∼0.2 m/ky), hinting at the possible intervention of local tectonism. Despite its height, the study area, Jeongdongjin Terrace, is associated with relatively young dates obtained by IRSL and cosmogonic Be-10, which strongly suggests the influence of local tectonism. However, clear evidence is yet to be found. This study attempts to investigate evidence of faulting activities and their timing and suggest its geomorphological implications for the coastal terrace development in relation to local tectonic movements. From the fieldwork, diverse fault markers, including fault lines, gouges, and colluvial wedges, were found beneath the uppermost clay layer, a sedimentary bed as thick as 3 m apparently had been deformed. Considering the ages of the pIRIR225 from the lower part of the deposit along with OSL dates and the presence of the AT tephra in the upper part of the bed, it is estimated that fault activity in the study area had occurred approximately between 210 and 30 ka, supporting the idea that the Jeongdongjin area had experienced several episodes of local uplifting relatively recently.