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Acoustic Properties of Gassy Sediments: Preliminary Result of Jinhae Bay, Korea  

Kim, Gil-Young (Petroleum & Marine Resources Division, Korea Institute of Geoscience and Mineral Resources (KIGAM))
Kim, Dae-Choul (Department of Environmental Exploration Engineering, Pukyong National University)
Yeo, Jung-Yoon (Gematek Corporation)
Yoo, Dong-Geun (Petroleum & Marine Resources Division, Korea Institute of Geoscience and Mineral Resources (KIGAM))
Publication Information
The Journal of the Acoustical Society of Korea / v.26, no.1E, 2007 , pp. 33-38 More about this Journal
Abstract
Compressional wave velocity and shear wave velocity were measured for gassy sediments collected from Jinhae Bay, Korea. To distinguish inhomogeneities of gassy sediments, Computed Tomography (CT) was carried out for gassy sediment using CT Scanner. The cored sediments are composed of homogeneous and soft mud (greater than $8{\Phi}$ in mean grain size) containing clay content more than 50%. In depth interval of gassy sediments, compressional wave velocity is significantly decreased from 1480m/s to 1360m/s, indicating that the gas greatly affects compressional wave velocity due to a gas and/or degassing cracks. Shear wave velocity shows a slight increasing pattern from ${\sim}55\;m/s$ in the upper part of the core to ${\sim}58\;m/s$ at 320 cm depth, and then decreases to ${\sim}54\;m/s$ in the lower part of the core containing a small amount of gas. But shear wave velocity in the gassy sediments is slightly greater than that of non-gassy sediments in the upper part of the core. Thus, the Vp/Vs ratio is decreased (from 30 to 25) in gas charged zone. The Vp/Vs ratio is well correlated with shear wave velocity, but no correlation with compressional wave velocity. This suggests that low concentrations of gas have little affects on shear wave velocity. By CT images, the gas in the sediments is mostly concentrated around inner edge of core liner due to a long duration after sediment collection.
Keywords
acoustic properties; gas bubble; CT scanner; gassy sediments; Jinhae Bay;
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Times Cited By KSCI : 2  (Citation Analysis)
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