SUNG-JA CHOI, KIGAM (Republic of Korea)
DUK-GEUN HONG, KANGWON NATIONAL UNIVERSITY (Republic of Korea)
UEECHAN CHWAE, KIGAM (Republic of Korea)
Taekmo Shim, KINS (Republic of Korea)
YUNGOO SONG, YONSEI UNIVERSITY (Republic of Korea)
There are over 36 Quaternary faults which have found in the southeastern part of Korean Peninsula. Among them, two Quaternary faults are located at the coastal area and cut marine terraces (T3) defined as MIS 5e. One of two, named as Suryum fault, was considered as no big effect of paleo-seismicity because its length is less than ∼150-m with only one fault event. The inner edge of the upper part of the T3 platform at Suryum is at ∼48 m above msl. In a quarry exposure of the platform (43-m), 2 m of stratified beach sediments consist mostly of yellowish brown, well sorted and weathered discoidal to sub-spherical pebbles. Overlying the beach gravels is a thin (<0.5 m) cap of yellow-brown fine sand and silt, possibly loess. A soil formed in the upper part of the sediments on the T3a platform at Suryum consists of a grayish-brown (7.5 YR 4/3) A-horizon, light grayish brown (7.5YR 6/6) EB-horizon, brown (7.5 YR 5/5) B-horizon, reddish brown (5 YR 5/4) BC-horizon, and light reddish brown (2.5 YR 6/4) C-horizon. In the hanging wall block of the reverse fault, having 70-cm vertical throw, that cuts the T3a platform and gravel at Suryum, the platform is very irregular and fractured. Recently, we obtained the new OSL age data from soil layers of the fault exposure and carried out retro-deformation to analysis evolution of the fault movement. Age of top soils ranges from 23 ka to 2 ka. The oldest one of them, 23 ka, should be age of original soil formation. Two others, 12 ka and 2 ka, are interpreted as re-deposition age of the soil formation after fault events of the latest Pleistocene to Holocene. According to retro-deformation of the fault, its active tectonic regime is analyzed to involve at least three-times events: the first is reverse movement which occurs between 23 ka to 12 ka, the second listric before 2 ka, and the third reverse again after 2 ka.