• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.4
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• pp.335-345
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• 2000

Physical and acoustic properties of the Southeastern Yellow Sea Mud (SEYSM) of Korea were studied by using 10 piston cores. The data were also compared with mudbelt sediments in the South Sea and the East Sea (southeastern inner shelf) of Korea. The sediments were mainly composed of homogeneous silt. Sandy mud and mud were minor components. The major source of sediment in the study area is probably the Keum River. Finegrained sediments discharged from the river are transported southward by coastal current, resulting in a gradual southward increase in porosity and a decrease in wet bulk density and sound velocity. The mean grain size especially appears to be the most important variable to determine the physical properties and velocity. The variations of physical properties with burial depth are dependent more strongly on sediment texture (especially, silt content) than compaction and/or consolidation. Correlations between the physical properties and the sediment texture show slight deviations from those of the East Sea and the South Sea of Korea in spite of similar pattern within the limiting values. This is probably due to the differences in silt contents, sedimentary environments, mineral compositions, and gas contents.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.52-59
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• 2008

We have developed a new deep-towed marine DC resistivity survey system. It was designed to detect the top boundary of the methane hydrate zone, which is not imaged well by seismic reflection surveys. Our system, with a transmitter and a 160-m-long tail with eight source electrodes and a receiver dipole, is towed from a research vessel near the seafloor. Numerical calculations show that our marine DC resistivity survey system can effectively image the top surface of the methane hydrate layer. A survey was carried out off Joetsu, in the Japan Sea, where outcrops of methane hydrate are observed. We successfully obtained DC resistivity data along a profile ${\sim}3.5\;km$ long, and detected relatively high apparent resistivity values. Particularly in areas with methane hydrate exposure, anomalously high apparent resistivity was observed, and we interpret these high apparent resistivities to be due to the methane hydrate zone below the seafloor. Marine DC resistivity surveys will be a new tool to image sub-seafloor structures within methane hydrate zones.