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ABSTRACT: Acoustic property of gas-bearing sediment in the southeastern shelf of Korea

Kim, Dae Choul, Young K. Seo, Gil Y. Kim , Pukyong National University, Pusan, South Korea

Laboratory determination of physical, acoustic and electrical properties on nine piston core samples in the southeastern part of Korea was carried out to understand acoustic behavior of gas-bearing sediments. Among them two cores penetrated the gas charged zone. The study area is characterized by its high surface productivity. Upwelling is common along the coastline of the southeast of Korea including the study area. Holocene mud derived from nearby Nakdong River deposits as a belt following the flowing pattern of the warm Tsushima Current. This area is a part of the mud belt that predominating inner shelf of Korean Peninsula. The acoustic property of the gas-bearing sediment is significantly different from that of adjacent mud belt sediments with similar textures. Acoustic velocity decreases abruptly 200 - 250 m/s at the gas charged zone without any substantial changes in other physical properties such as porosity and density. It is clear that even in small amounts of gas bubbles affects acoustic behavior of marine sediments. Good correlation is also existed between velocity and electrical resistivity at the gas charged zone. The gas bubbles also discourage electrical current flow that results in increase in electrical resistivity. Confused signals are observed for the vane shear strength tests. Different from other normal cores shear strengths are rather slightly increased or at least stay on line with subbottom depth. Although quantitative and detailed in situ analysis are not available, X-radiography photos on cores indicate the existence of randomly oriented coin-shaped degassing cracks.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia