Econ. Environ. Geol. 2012; 45(5): 513-523

Published online October 31, 2012

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Acoustic Characteristics of Gas-related Structures in the Upper Sedimentary Layer of the Ulleung Basin, East Sea

Hyun-Tak Park1, Dong-Geun Yoo2, Hyuk-Soo Han3, Jeong-Min Lee3 and Soo-Chul Park1*

1Department of Oceanography and Ocean Environmental Sciences, Chungnam National University, DaeJeon 305-764, Korea
2Petroleum and Marine Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), DaeJeon 305-350, Korea
3Korea Seabed Information (KOSBI) Corporation, DaeJeon 306-020, Korea

Correspondence to :

Soo-Chul Park

scpark@cnu.ac.kr

Received: September 4, 2012; Accepted: October 11, 2012

Abstract

The upper sedimentary layer of the Ulleung Basin in the East Sea shows stacked mass-flow deposits such as slide/slump deposits in the upper slope, debris-flow deposits in the middle and lower slope, and turbidites in the basin plain. Shallow gases or gas hydrates are also reported in many area of the Ulleung Basin, which are very important in terms of marine resources, environmental changes, and geohazard. This paper aims at studying acoustic characteristics and distribution pattern of gas-related structures such as acoustic column, enhanced reflector, dome structure, pockmark, and gas seepage in the upper sedimentary layer, by analysing high-resolution chirp profiles. Acoustic column shows a transparent pillar shape in the sedimentary layer and mainly occurs in the basin plain. Enhanced reflector is characterized by an increased amplitude and laterally extended to several tens up kilometers. Dome structure is characterized by an upward convex feature at the seabed, and mainly occurs in the lower slope. The pockmark shows a small crater-like feature and usually occurs in the middle and lower slope. Gas seepage is commonly found in the middle slope of the southern Ulleung Basin. These gas-related structures seem to be mainly caused by gas migration and escape in the sedimentary layer. The distribution pattern of the gas-related structures indicates that formation of these structures in the Ulleung Basin is controlled not only by sedimentary facies in upper sedimentary layer but also by gas-solubility changes depending on water depth. Especially, it is interpreted that the chaotic and discontinuous sedimentary structures of debris-flow deposits cause the facilitation of gas migration, whereas the continuous sedimentary layers of turbidites restrict the vertical migration of gases.

Keywords Ulleung Basin, gas-related structures, chirp seismic profiles, acoustic characteristics

Article

Econ. Environ. Geol. 2012; 45(5): 513-523

Published online October 31, 2012

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Acoustic Characteristics of Gas-related Structures in the Upper Sedimentary Layer of the Ulleung Basin, East Sea

Hyun-Tak Park1, Dong-Geun Yoo2, Hyuk-Soo Han3, Jeong-Min Lee3 and Soo-Chul Park1*

1Department of Oceanography and Ocean Environmental Sciences, Chungnam National University, DaeJeon 305-764, Korea
2Petroleum and Marine Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), DaeJeon 305-350, Korea
3Korea Seabed Information (KOSBI) Corporation, DaeJeon 306-020, Korea

Correspondence to:

Soo-Chul Park

scpark@cnu.ac.kr

Received: September 4, 2012; Accepted: October 11, 2012

Abstract

The upper sedimentary layer of the Ulleung Basin in the East Sea shows stacked mass-flow deposits such as slide/slump deposits in the upper slope, debris-flow deposits in the middle and lower slope, and turbidites in the basin plain. Shallow gases or gas hydrates are also reported in many area of the Ulleung Basin, which are very important in terms of marine resources, environmental changes, and geohazard. This paper aims at studying acoustic characteristics and distribution pattern of gas-related structures such as acoustic column, enhanced reflector, dome structure, pockmark, and gas seepage in the upper sedimentary layer, by analysing high-resolution chirp profiles. Acoustic column shows a transparent pillar shape in the sedimentary layer and mainly occurs in the basin plain. Enhanced reflector is characterized by an increased amplitude and laterally extended to several tens up kilometers. Dome structure is characterized by an upward convex feature at the seabed, and mainly occurs in the lower slope. The pockmark shows a small crater-like feature and usually occurs in the middle and lower slope. Gas seepage is commonly found in the middle slope of the southern Ulleung Basin. These gas-related structures seem to be mainly caused by gas migration and escape in the sedimentary layer. The distribution pattern of the gas-related structures indicates that formation of these structures in the Ulleung Basin is controlled not only by sedimentary facies in upper sedimentary layer but also by gas-solubility changes depending on water depth. Especially, it is interpreted that the chaotic and discontinuous sedimentary structures of debris-flow deposits cause the facilitation of gas migration, whereas the continuous sedimentary layers of turbidites restrict the vertical migration of gases.

Keywords Ulleung Basin, gas-related structures, chirp seismic profiles, acoustic characteristics

    KSEEG
    Jun 30, 2024 Vol.57 No.3, pp. 281~352

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