HR: 0800h
AN: OS51C-01    [Abstracts]
TI: Physical and Acoustic Properties of Gas-bearing Sediments in Jinhae Bay, the South Sea of Korea
AU: * Kim, D C
EM: dckim@pknu.ac.kr
AF: Dae C. Kim, Namgu Daeyondong 599-1, Busan, 608-737, Korea, Republic of
AU: Lee, G S
EM: cooks@mail1.pknu.ac.kr
AF: Dae C. Kim, Namgu Daeyondong 599-1, Busan, 608-737, Korea, Republic of
AU: Lee, G H
EM: gwanglee@pknu.ac.kr
AF: Dae C. Kim, Namgu Daeyondong 599-1, Busan, 608-737, Korea, Republic of
AU: Park, S C
EM: scpark@cnu.ac.kr
AF: Soo C. Park, Yusonggu Gungdong 220, Daejon, 305-764, Korea, Republic of
AB: High-resolution seismic survey and sediment core sampling were conducted to investigate acoustic characteristics of gas-bearing sediments in Jinhae Bay, the southeast of Korea. . The sediment in the Jinhae Bay is mostly homogenous mud deposited after Holocene transgression. Along with the 410 km of chirp seismic profiling, 13 piston core samples were collected on the track lines. Gassy sediments are common and widely occurred in the bay. Core samples were analyzed for physical properties (porosity, water content, bulk density, grain density and shear strength), acoustic properties (compressional wave velocity and attenuation), and electrical resistivity. Pulse transmission technique (1 MHz) that programmed to pick up first arrival signal was used to calculate accurate velocity. Electrical resistivity was measured by the standard four electrode method. Sediment texture was also analyzed using sedimentation method. Subsampling interval was 10 cm. X- radiograph image analysis was also performed to observe the shape of degassing cracks. Both quantitative and composition analyses of free gas were carried out for the cores of gas zone. Carbon isotope was also determined for the origin of the gas. There is no significant downcore variation on physical and sediment textures regardless of existence of gas bubbles. However, velocity dramatically decreases from average 1480 to 1350~911 m/s for the cores that penetrate the gas-bearing zones. This is probably due to degassying cracks which developed by escaping gases and free gas bubbles that still trapped in the cores. Electrical resistivity is the only geotechnical property increase in the gas-bearing zone where velocity decreases abruptly. This indicates the possibility of electrical resistivity as an index variable as well as velocity for sediment microstructure because there is little changes in texture and composition of sediment. Methane is a dominant component with about 5% average content in the gassy zones. The carbon isotope analysis suggests that the shallow gas in Jinhae Bay is biogenic origin.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3004 Gas and hydrate systems
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly