동해 남서 울릉분지에서의 제 4기 후기(<29.4 cal kyr BP) 해저사면사태의 발생 및 특성 변화

Abstract

Detailed analysis of depositional characters and ages of turbidites from the southwestern Ulleung Basin reveals changes in frequency, failing area and dimension of slope failures after 29.4 cal kyr BP. Abundant thin- to thick-bedded turbidites between 29.4 and 19.1 cal kyr BP indicate that various-scale slope failures occurred frequently during the last glacial period. When sea level was lowest (20.0-19.1 cal kyr BP), larger-scale slope failures occurred, forming very thick turbidites. Occurrence and thickness of turbidites decreased after 19.1 cal kyr BP when sea level began to rise, reflecting decrease in frequency and dimension of slope failures. The upward change from muddy to sandy turbidites around 21.4 cal kyr BP indicates that failing areas retrograded upslope from the upper-middle muddy slope to the uppermost sandy slope when sea level was nearly lowest. In the southwestern slope of the basin, frequent slope failures during the last glacial period suggest that slope failures were mostly triggered by earthqukes associated with active decomposition of gas hydrate during sea-level lowering.