Distribution and Acoustic Characteristics of Shallow Gas in the Korea Strait Shelf Mud off SE Korea |
| |
Authors: | Dae Choul Kim Gwang Hoon Lee Young Kyo Seo Gil Young Kim Seok Yun Kim Jeong Chang Kim Soo Chul Park Roy Wilkens |
| |
Affiliation: | a Pukyong National University, Department of Environmental Exploration Engineering, Busan, Koreab Pukyong National University, Department of Oceanography, Busan, Koreac Chungnam National University, Department of Oceanography, Daejon, Koread University of Hawaii, Hawaii Institute of Geophysics and Planetology, Honolulu, Hawaii, USA |
| |
Abstract: | Shallow gas in the Korea Strait shelf mud (KSSM) off SE Korea, revealed by high-resolution subbottom profiles, is associated with acoustic blanking, acoustic turbidity, seepages with plumes in the water column, and seafloor depressions. The acoustic blanking, characterized by strong, consistent top reflection and wipeout below, is most dominant. The seaward edge of the acoustic blanking zone generally coincides with the 100-m water-depth contour, suggesting that the water depth (the pressure) may control the distribution of shallow gas. The acoustic turbidity, characterized by diffuse top reflection, is a dark smear, partially blanking the data below. The seepages with plumes, characterized by vertical smearing and disturbed seafloor, are seen only along the shallowest, landward edge of the acoustic blanking zone. This may suggest that the decreased gas solubility at shallow water depths, caused by the lowered pressure, increases the volume of free gas in the sediments, facilitating the gas escape. The seafloor depressions, interpreted as pockmarks, are accompanied by cone-shaped acoustic masking, which is probably the reflection from a narrow vent of gas. The gas-related acoustic anomalies appear to occur mostly in the upper, recent mud of the KSSM. Neither permeable beds nor faults, which can act as vertical migration pathways for deep thermogenic gas, are evident in the recent mud. We interpret that the bacterial degradation of organic matter in situ is the main source for the gas in the KSSM. The upwelling off SE Korea may be an important source for the increased organic matter in the area. |
| |
Keywords: | shallow gas acoustic blanking acoustic turbidity Korea Strait shelf mud |
本文献已被 InformaWorld 等数据库收录! |
|