• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.142-151
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• 2001

Detailed interpretation of some high-resolution seismic profiles in Yosu Strait reveals that Late Quaternary deposits consist of three allostratigraphic units (UH, LH, PL) formed by fluvial and tidal controls. The top mud unit, UH, thins onshore, and overlies the backstepping modem Seomjin delta deposits, which is interpreted as a transgressive systems tract (757) related to Holocene relative sea-level rise. The unit LH below the unit UH is composed of delta, valley- and basin-fill facies. The delta facies (Unit $LH_1$) occurs only in Gwangyang Bay and shows two prograding sets retrogradationaly stacked, thus it is also interpreted as a transgressive systems tract(757). On the contrary, the valley- and basin-fill facies (Unit $LH_2$), interpreted as 757, occur between the units UH and PL (Pleistocene deposits) in Yosu Strait. The bounding surface between UH and $LH_2$ can be interpreted as a tidal ravinement surface on the basis of trends thinning toward inner bay and becoming young landward. Furthermore its geomorphological pattern is similar to that of recent tidal channels. This allostratigraphy in'ffsu Strait suggests that two 757 deposits (UH and $LH_2$), divided by tidal ravinement surface, have been formed in Yosu Strait, whereas in Gwangyang Bay backstepping delta deposits ($LH_1$) without tidal ravinement surface have been formed during Holocene sea-level rise. These characteristics indicate that different stacking patterns could be formed in these two areas according to different increasing rate of accommodation space caused by different geomorphology, sediment supply and tidal-current patterns even in the same period of Holocene sea-level rise.

• Journal of the Korean association of regional geographers
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• v.13 no.1
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• pp.32-42
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• 2007

In Sagye coast of Andeok-myeon, southwestern Jeju, shore platform of noncohesive Hamori Formation, marine terrace deposit of round gravels, coastal dune composed of shell sand and volcanic sand, and back lake are linked closely with each other. In this paper, the formation process of Sagye coastal geomorphic system analysed by using OSL dating method is as follows: Firstly, Hamori Formation is a horizontal stratum filed up of tuff reworked by submarine volcanic eruption during 3$\sim$7.6 ka BP. Hollow at the boundary between Hamori Formation' flat and Kwangheak Basalt's gentle slope become a back lake when block is appeared over the sea level by uplift. Secondly, while Hamori Formation was laid below sea level, gravels which had been broken and abraded at southwestern rocky coast composed of Kwangheak basalt or been transported through the small stream from adjacent hillslope were deposited in rapid flow environment. Thirdly, deposition of round gravels was ceased by earth uplift, and shore platform was constructed by abrasion process of energy of swash moving forward. As altitude of shore platform is equal to high tidal level of spring tide, compared it with present high tidal level of study area, earth is uplifted about 105m since shore platform was formed. Fourthly, much sandy sediments transported from offshore bottom covered shore platforms and marine terrace deposits. Lighter sediments among sandy sediments was blown to back, formed secondary sand dune since about 500 year.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.4
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• pp.343-349
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• 2011

Seabed topography and marine site survey should be performed first in the design and construction of marine structures. We could successfully acquire the seafloor topography information can be obtained by bathymetric survey and side scan sonar and the sediment layer thickness and 3D bedrock depth by seismic reflection. It is necessary to apply carry out the integrated interpretation to each other in the ocean civil Eng. In this paper, we have obtained information on the sea bottom topography and water depth at the same time using interferometer technique and on the basement depth by seismic reflection. We have performed to assess the proposed method on the seafloor topographic survey with bedrock.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.424-431
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• 2009

This study investigates the difference of sound velocity (compressional wave velocity) between gas hydrate-bearing sediments and nongas hydrate-bearing sediments in the Ulleung Basin, East Sea. We use a dataset measured from one site in the central part of the Ulleung Basin. Sound velocity for gas hydrate-bearing sediment shows the range from 1600 m/s to 2200 m/s. However, the value for nongas hydrate-bearing sediment is mostly around 1500 m/s, being less than 1400 m/s below 140 m subbottom depth. This trend is probably due to the presence of free gas below BSR (Bottom Simulating Reflector). Gas hydrate-bearing sediments show high value (maximum 150 Ohm-m) of resistivity. The physical properties between gas hydrate-bearing sediment and nongas hydrate-bearing sediment are characterized by the different patterns due to the presence of gas hydrate in comparison with those of marine unconsolidated sediments. Therefore, in order to investigate acoustic and physical properties for gas hydrate-bearing sediments, the study for the occurrence type and the amount of gas hydrates should be conducted simultaneously.

• The Korean Journal of Petroleum Geology
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• v.5 no.1_2 s.6
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• pp.9-15
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• 1997

The study area is located in the Central Bransfield Basin, Antarctica. To analyze the morphology of seafloor, structure of basement, and seismic stratigraphy of the sedimentary layers, we have acquired, processed, and interpreted the multi-channel seismic data. The northwest-southeastern back-arc extension dramatically changes seafloor morphology, volcanic and fault distribution, and basin structure along the spreading ridges. The northern continental shelf shows a narrow, steep topography. In contrast, the continental shelf or slope in the south, which is connected to the Antarctic Peninsula, has a gentle gradient. Volcanic activities resulted in the formation of large volcanos and basement highs near the spreading center, and small-scale volcanic diapirs on the shelf. A very long, continuous normal fault characterizes the northern shelf, whereas several basinward synthetic faults probably detach into the master fault in the south. Four transfer faults, the northwest-southeastern deep-parallel structures, controlled the complex distributions of the volcanos, normal faults, depocenters, and possibly hydrocarbon provinces in the study area. They have also deformed the basement structure and depositional pattern. Even though the Bransfield Basin was believed to be formed in the Late Cenozoic (about 4 Ma), the hydrocarbon potential may be very high due to thick sediment accumulation, high organic contents, high heat flow resulted from the active tectonics, and adequate traps.

• Journal of the Korean Geophysical Society
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• v.2 no.1
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• pp.39-44
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• 1999

High-resolution images are drawn from existing seismic data which were originally obtained by Korea Ocean Research & Development Institute (KORDI) during 1994-1997 for deep seismic studies on the East Sea of Korea. These images are analyzed for mapping Quaternary faults and near-bottom gas pockets. First 12 channels are selected from shot gathers for reprocessing. The processing sequence adopted for high-resolution seismic images comprises data copy, trace editing, true amplitude recovery, common-midpoint sorting, initial muting, prestack deconvolution, bandpass filtering, stacking, highpass filtering, poststack deconvolution, f-x migration, and automatic gain control (AGC). Among these processing steps, predictive deconvolution, highpass filtering, and short window AGC are the most significant in enhancement of resolution. More than 200 Quaternanry faults are interpreted on the migrated sections in the shallow depths beneath the seafloor. Although numerous faults are found mostly at the western continental slope and boundaries of the Ulleung Basin, significant amount of the faults are also indicated within the basin. Many of these faults are believed to be formed with reactivation of basement, from geotectonic activities including volcanism, and often originated in Tertiary, indicating that the tectonic regime of the East Sea might be unstable. Existence of shallow gas pockets casts real hazardous warnings to deep-sea drillings and/or to underwater constructions such as inter-island cables and gas pipelines. On the other hand, discovery of these gas pockets heightens the interests in developing natural resources in the East Sea. Reprocessed seismic sections, however, show no typical seismic characteristics for gas hydrates such as bottom-simulating reflectors in the western continental slope and ocean floor.

• Economic and Environmental Geology
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• v.9 no.4
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• pp.213-223
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• 1976

Proceeding from general elementary principles to more specific abstract problems, we have attempted the rearrangement of the research results as they are known at present concerning the propagation and attennation of the elastic wave in submarine layers. We have derived the elementary equations of the elastic wave. In addition, the relationship of the propagation of the elastic waves in the sea water mass and the reflection of the waves from the water-sediment interface are treated and presented in different sections.

• Journal of the Korean Geophysical Society
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• v.7 no.3
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• pp.193-206
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• 2004

Geophysical data including chirp (3 7 kHz) subbottom profile and detailed bathymetry were obtained over three seamounts in the Ogasawara Fracture Zone (OFZ) of the western Pacific, as a part of manganese crust survey onboard R/V Onnuri in 2003. The OFZ is a 150-km-wide, 600-km-long rift zone, which separates the East Mariana and Pigafetta Basin. The OFZ is unique in that it includes many seamounts (e.g., Magellan Seamounts andseamounts on the Dutton Ridge). The sub-seafloor acoustic echoes obtained near the OFZ were classified into following types on the basis of their characteristics: types I-1(pelagic sediment with parallel or subparallel reflectors), I-2 (pelagic sediment with no internal reflectors), and III-1 (reef build-up complex) on summit; types II-1 and III-2 (basement outcrop) on flank rift zone and upper slope, respectively; type III-3 (slump) on the lower slope and embayment between the flank rift zones; types II-2 (debrite) on the base of slope and basin floor; and types II-3 (turbidite or pelagic sediment) and II-4 (turbidite) on the basin floor. The mass-wasting that produced the complex of type II-2 debrite and III-3 slump on the lower slope and basin may have been caused by (1) strong tensional stress in the OFZ which may cause the numerous fissures or basement faults and (2) complex of the faults on the summit and steep upper slope. The variations in the echo type of pelagic sediment in the summit of seamounts may be related with the changes in the depositional and/or erosional environments. Type I-2 pelagic sediment, which is characterized by a thin and intermittent coverage, was probably deposited at a sheltered area when the current was strong, whereas type I-1 pelagic deposit occurred during a stage of progressive sedimentation.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.2
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• pp.90-101
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• 2009

Analysis of multi-channel seismic reflection data from the Southern Ulleung Basin reveals that Plio-Quaternary section in the area consists of nine stacked sedimentary units separated by erosional unconformities. On the southern slope, these sedimentary units are acoustically characterized by chaotic seismic facies without distinct internal reflections, interpreted as debris-flow bodies. Toward the basin floor, the sedimentary units are defined by well-stratified facies with good continuity and strong amplitude, interpreted as turbidite/hemipelagic sediments. The seismic facies distribution suggests that deposition of Plio-Quaternary section in the area was controlled mainly by tectonic movement and sea-level fluctuations. During the Pliocene, sedimentation was mainly controlled by tectonic movements related to the back-arc closure of the East Sea. The back-arc closure that began in the Miocene caused compressional deformation along the southern margin of the Ulleung Basin, resulting in regional uplift which continued until the Pliocene. Large amounts of sediments, eroded from the uplifted crustal blocks, were supplied to the basin, depositing Unit 1 which consists of debris-flow deposits. During the Quaternary, sea-level fluctuations resulted in stacked sedimentary units (2-9) consisting of debris-flow deposits, formed during sea-level fall and lowstands, and thin hemipelagic/turbidite sediments, deposited during sea-level rise and highstands.

• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.1-6
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• 1999

Natural gas hydrate, a solid compound of natural gas (mainly methane) and water in the low temperature and high pressure, is widely distributed in permafrost region and deep sea sediments. Gas hydrate stability field (GHSF), which corresponds to the conditions of a stable existence of solid gas hydrate without dissociation, depends on temperature, pressure, and composition of gas and interstitial water. Gas hydrate-saturated sediment are easily recognized by the bottom simulating reflector (BSR), a strong-amplitude sea bottom-mimic reflector in seismic profiles. It is known that BSR is associated with the basal boundary of the GHSF, The purpose of this study is to define the GHSF and its occurrence in the southwestern part of Ulleung Basin, East Sea. The hydrothermal gradient is measured using the expandable bathythermograph (XBT) and the geothermal gradient data are utilized from previous drilling results for the adjacent area. By the laboratory work using methane and NaCl $3.0 wt{\%}$ solution, it is shown that the equilibrium pressures of the gas hydrate reach to 2,920.2 kPa at 274.15 K and to 18,090 kPa at 289.95 K for the study area. Consequently, it is interpreted that the lower boundary of the GHSF is about 210 m beneath 400-m-deep sea bottom and about 480 m beneath 1,100-m-deep sea bottom. The resultant boundary is well matched with the depth of the BSR obtained from the seismic data analysis for the study area.