UPLIFT RATE AND RELATED ACTIVE FAULTING OF KOREAN PENINSULA

Korean peninsula has the rias coast to the south and the west. The largest tidal range is 8m at the middle part of the western coast. Holocene marine terrace is developed on the rias coast. However, the late Pleistocene terraces, generally showing intermittent extension and very narrow widths, are abundant along the east coast. Digital terrace mapping and active fault survey have been done simultaneously for the morphotectonic evaluation of the peninsula. The east coast has three representative MIS 5 terraces; 10m of 5a, 20m of 5c, and 30m of 5e. Some terraces show 18m of 5a, 33m of 5c, and 45m of 5e due to differential uplift, which shows locally higher Holocene terrace of 3.5m than that of other ordinary terraces. The west coast shows gradational height decrease from the mid-west to the southwest. The height of 5e-terrace shows 8m on the mid-west coast, 1m on the southwest, and the below from the present sea level at the southwestern tip. Terrace age is based on OSL (optically stimulated luminescence) data, which is 60ka for 5a and 100ka for 5e. It reveals that the east coast has higher uplift compared to the west and that the west coast has been tilted to the south. The uplift rate of the east coast is 0.2-0.3m/ky and the west is 0.01m/ky. Two neotectonic faults striking to NNE cross the peninsula from the north to the south and are parallel each other with right lateral strike-slip movement sense. Both of them formed during the late Cretaceous and have been reactivated until the late Pleistocene. Structural segmentation ranges from 4km to 500m. Since after 15Ma, the southeastern margin block (Yonil) of the east faults (Yangsan-Ulsan faults) had been rotated to the clockwise due to the northward subduction of Philippine Plate. The rotation gave an effect of widening the East Sea until the lowest Pliocene (5Ma). The sea is closing because of the westwards movement of Pacific Ocean Plate. GPS vectors indicating WNW immediately throw down after penetrating the west fault (Chugaryong fault), which brought the differential uplift of the peninsula. Morphotectonically, it reveals that the peninsula is tilted to the west and the southwest, accompanying the westward reverse faulting, and that 5e terrace sediments of the east coast are faulted with top-up-to-the-west reverse sense. Fault movement occurred three times during the late Pleistocene.