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