chirp subbottom profile 자료를 이용한 태평양 오가사와라 균열대 주변 다섯 해저산들의 지형 변화 연구

Abstract

The multibeam bathymetric and chirp (3-7 kHz) subbottom data used in this study were obtained during a reconnaissance survey of seamounts in the west Pacific for ferromanganese crusts by KORDI onboard R/V Onnuri during 2000 and 2003. In this study, we construct detailed echo-type maps based on chirp subbottom profile. These map show extensive mass-wasting processes and features related with flank evolution of seamounts in the Ogasawara Fracture Zone (OFZ) of the west Pacific. A total of nine different echo types were identified based on the clarity of echo, subbottom structure and morphology of the seafloor. Pelagic sediment of types I-1, I-2 and type III-1 reef build-up complex are found on the flat summits; basement outcrop of types II-1 and III-2 on the flank rift zones, slopes and hills; type III-3 slump on the lower slope and the embayment between the flank rift zones; type II-2 debrite on the base of slope; and turbidite of types II-3 and II-4 on the basin floor. Large mass-wasting may be triggered by earthquakes, dike intrusion, caldera collapse, weakening of volcanic rocks by hydrothermal fluids, reactivation of basement faults, etc. There are two possibilities that the mass-wasting of the west study is well-developed. The first is that the strong tensional stress in the OFZ makes some fissures or basement faults in the fracture zone and intrusions occur. The magnetic anomaly lineation M35 between the PB and EMB suggests that there has been about 600-km-long movement between them. The OFZ, seamounts, and associated flexural moat separate the PB and EMB. These strong stresses may make basement faults and/or fissures. Another cause may be the complex of the faults on the summit, steep upper slope, and closeness to the Mariana Trench. The slope failure in the study area started on the margin of summit and upper slope. The steep upper slope and faults on the summit in the west study area are easy to cause the mass-wasting by shear stresses above cri