• 한국해양학회지
• /
• v.27 no.1
• /
• pp.66-77
• /
• 1992

Tidal sand ridges and sand waves are well developed in the Yellow Sea off Tae-An Peninsula, Korea. Their transport directions were inferred based on high resolution seismic profiles, surficial sediment characteristics and tidal regime. Tidal sand ridges are asymmetric, with long axes parallel to or slightly oblique to the dominant NE-SW tidal current direction. They show steep south and/or southeast flanks, which are in concordance with the apparent direction of internal cross-bedding in the south. Holocene sediments occur in accordance with distributional patterns of tidal sand ridges. These features indicate that Holocene active tidal sand ridges move toward the open sea in southeast, south and southwest direction. Sand waves which are distributed in flat sea floor with depth of about 40-60m show also asymmetric forms with a steep east-to-northeast face. Surficial sediments in the sand wave field are characterized by well sorted fine sands compared with poorly sorted adjacent areas. The sand waves appear to undergo easterly or northeasterly landward movement.

• The Korean Journal of Petroleum Geology
• /
• v.9 no.1_2 s.10
• /
• pp.16-23
• /
• 2001

The study area in the East Sea is located on the northeastern margins of the Ulleung Basin near the Kita-Yamato Bank. The research area provides the important clue to the development of Miocene basins which are characterized by the normal faults and volcanic activities related to rifting in the continental crust. Kita-Yamato Bank is a small sediment-filled graben which was formed by failed rifting in the Early Miocene. The basins rapidly vary the bathymetry, depth of acoustic basement and thickness of sedimentary layer. The tension in the study area caused the extensional lithospheric deformation before/during the Early Miocene. In consequence, tectonic forces resulted in the depression or subsidence of basement from continental rifting in the Kita-Yamato Bank followed by the opening of the Ulleung Basin, and caused the onset of graben or half-graben structure bounded by large blocked syn-rift faults. Afterward no significant tectonic deformation exists, with the consequence that post-rift normal faults with small heave were formed and reactivated by the resultant forces such as tectonic subsidence, sediment loading and volcanic activity. The Cenozoic sediment layer has a maximum thickness of 1.0 s along the center of the graben or half-graben, which overlies the consolidated acoustic basement. Seismic units V and IV supposed to be syn-rift sedimentary rocks are deformed by both the volcanic activities and numerous basement-involved normal faults induced from extension. In the uppermost layer, slump scars resulted from the slope failure are recognized.

• Korean Journal of Microbiology
• /
• v.34 no.4
• /
• pp.183-187
• /
• 1998

In order to characterize the microbial distribution at sediments of Lake Daechung, soil samples were collected at two depths of 0.5~2 cm and 19~21 cm of Chudong(static) and Hoenam(streaming) site on May 18th(before rainy season) and on August 24th in 1998(after rainy season), and then the density(CFU/g soil) of microorganisms including bacteria, actinomycetes, and fungi was investigated by the viable cell counting method. Microbial density at streaming site was on the whole 3.9-fold higher than that at static site. Bacterial densities examined before and after rainy season was revealed to be similar, whereas actinomycetes and fungi exhibited higher distribution after and before rainy season, respectively. The microbial distribution was not generally reduced with the increase of depth and was rather higher at some deep sites. On comparing with the microbial densities of grass land around the lake, bacteria, actinomycetes, and fungi at lake sediments on the average showed the distribution of 52.9%, 35%, and 7%, respectively. However, their distribution except for fungi which exhibited 71.2% was mostly found to be somewhat higher than at the shore of lake.

• Journal of the Korean Geophysical Society
• /
• v.9 no.4
• /
• pp.343-349
• /
• 2006

In order to study unconsolidated sediments upstream of the Soyang Dam, seismic refraction data were recorded along five profiles of 94 m length. Receiver interval and record length were 2 m and 204 ms, respectively. Recorded data were analyzed using the traveltime tomography and delay-time methods in order to reveal sediment distribution in the investigation site. The acoustic basements are buried at approximately 14 m deep and their thickness shallows to southeast approaching to a hill. On the basement, pre-existing sediments deposited before construction of the Soyang dam lies. This sedimentary layer is composed of paleo-soil and sandy sediments. Above this layer, recent sediments comprise the top layer which is believed to have been deposited since the formation of the dam. Average thickness of this uppermost layer is approximately 1.6 m, which is much thicker than in the downstream.

• Journal of the Korean earth science society
• /
• v.44 no.6
• /
• pp.594-610
• /
• 2023

The horizontal-to-vertical spectral ratio (HVSR) has been widely applied to evaluate ground characteristics such as site response and thickness of the soft sedimentary layer on top of the bedrock via dominant frequencies and amplification factors of microtremors. Eight seismic stations were selected to investigate the HVSR results at the surface and at varying depths, and their variations due to wind speeds. These stations are equipped with seismic sensors on the surface and downhole(s) at depths. The borehole data analysis reveals that the geological condition at burial depth influences the HVSR results. Their dominant frequencies indicate the entire thickness of the soft layer, not the thickness to the bottom or top of the soft sedimentary layer from the seismometer burial depth. Analysis of the background noise observed at the surface showed that the resonance frequency estimation varied with wind speed changes. In the studied cases, the background noise observed in the sedimentary layer at depths of 20 to 66 meters yielded stable and consistent resonance frequency estimation regardless of wind speed fluctuations. The results of the seismic sensors buried deeper than 100 meters are unstable. The result indicates that the background noise from the buried seismometer at shallow depths (~0.3 m) under light wind conditions (wind speeds less than 3 m/s) is sufficient to achieve the purpose of the HVSR analysis.

• 한국해양학회지
• /
• v.20 no.1
• /
• pp.43-49
• /
• 1985

The Changgu Bay, a macrotidal coastal embayment of the west coast of Korea, is an area of extensive intertidal sedimentation. Three types of major sediment facies are identified based on grain size analysis: silt, sandy-silt, and silty-sand facies. It is found that intertidal sediment facies comprise a continuum of progressively finer sediments from lower flat to upper one. The X-radiography of the cores in the intertidal zone show a wide variety of physical and biogenic sedimentary structures. The major structures include bioturbation, current ripple and parallel-laminae. Bioturbations are observed in all core samples, especially in the silt flat zone. The degree of bioturbation increases laterally from sandy facies (low tide level) to silt facies (high tide level) due to favorable properties of fine mud for organisms. The ripple laminae, composed of current ripple foresets, characterize the silty-sand and sandy-silt flats. The parallel laminae are extensively bioturbated, and two types of laminae are distinguishable; thick-laminae with a thickness of 1 to 5mm and thin-laminae with a thickness of less than 1mm.

• Journal of the Korean Geophysical Society
• /
• v.7 no.2
• /
• pp.99-112
• /
• 2004

The Basin, a marginal basin located between the Antarctic Peninsula and the South Shetland Islands, is consist of three small basins, the Central, Eastern, Western Basins. Seismic data obtained on December 1995 show well-defined spreading ridges, basement highs, faults, morphology of the basin, distribution of sediments, crustal and sedimentary deformation, diapirs, and contourites. The main spreading axis of the Central Bransfield Basin connecting Deception and Bridgeman Islands continues up to the central part of the Eastern Basin, whereas deep basin covered by thick sediments without any spreading structures develops in the northeastern part. This indicates that back-arc spreading along the axis of the Bransfield Basin has been taken place in the southwestern part of the Eastern Basin, not in the northeastern part. Many NW-SE trending faults perpendicular to the axis of the basin would be related with strike-slip movement of the Shackleton Fracture. Zone. Extensinal strutures like deep basin without any spreading structures in the northeastern part, normal faults and diapirs on both continental slopes of the Eastern Basin would be formed by extension as a consequence of the sinistral movement between Antarctic and the Scotia plates.

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2004.06a
• /
• pp.223-224
• /
• 2004

고준위폐기물 혹은 사용후 핵연료의 처분용기 재질은 각 국의 처분개념과 처분공의 주위 환경에 따라 달라질 수 있다. 용기의 후보재질로는 탄소강, 스텐레스 강, 구리, 니켈, 티탄 혹은 이들의 합금이 주로 고려되고 있으나, 국내에서는 아직 선정되지 않았다. 국내 처분환경에서 이들 재질의 부식특성을 조사하고자 모의 화강암 지하수를 가해 만든 겔 상태의 경주 벤토나이트에 탄소강, 스텐레스 강, 구리 시편을 넣고, $70^{\circ}C$, 아르곤 분위기에서 530일 경과한 후 시편의 표면 변화 (그림 1) 및 무게 감소를 측정하였다. 철 부식시편은 검정색의 철 화합물 층으로 덮여 있었으며, 구리표면에는 노란색의 부식층이 형성되었는데, 이를 XRD로 분석한 결과 $Cu_2O$로 판명되었다. 그러나 $700^{\circ}C$에서 각각 0, 24, 96시간동안 예민화시킨 스텐레스 강 시편들은 모두 초기상태 그대로 광택을 유지하고 있었으며, XRD에서 다른 화합물의 형성을 발견할 수 없었다 (그림 2). 시편의 무게 감소가 균일부식에 기인한 것으로 가정하여 환산한 결과, 구리와 스텐레스 강 모두 0.3~0.4 $\mu\textrm{m}/yr$의 부식속도를 나타내었다. 그러나 구리는 부식생성물이 표면에 부착되어 있기 때문에 실제 부식두께는 이 값보다 더 클 것으로 생각된다. 용기가 초기 530일간과 같은 속도로 처분용기의 부식이 진행된다면 한국에서 기준처분 개념으로 삼고 있는 50mm 두께의 내부식성 외벽 금속용기는 적어도 만년이상 견딜 수 있을 것으로 추정된다. 한편, 검정색 부식층을 제거한 무게감소로부터 계산한 철의 부식속도는 구리의 약 30배에 해당하였다. 금속 재질의 정확한 부식 거동을 파악하기 위해서는 보다 장기간의 실험이 요구된다. 시험법 선정에 각계(규제기관, 학계, 발전소 현장 및 산업계 등) 전문가로부터 기술자문회의를 통하여 자문 의견을 받기로 하였다. 특히 현재 폐기물 인수 기술기준치가 설정된 국가의 시험법을 심층 있게 검토하기로 하였다.검토하기로 하였다. 혹은 수성주변 환경이 지배하는 산악이나 구릉지에서 흔히 나타나는 침엽수-낙엽활엽수의 혼합림 식생상태를 잘 대변해 주고 있는 것으로 판단된다. 끝으로, 의림지 호저 퇴적층 중에서 인위적인 교란흔적이 없는 암회색 유기질 니층에 대한 탄소연대측정 결과, 제1호공 12번 시료에서 950$\pm$40 years B.P을 얻었으며, 제3-1호공에서도 아래로 내려가면서 8, 10, 11번 시료에 대하여 500$\pm$30 years B.P, 650$\pm$30 years B.P, 800$\pm$40 years B.P의 연대측정 결과를 획득하였다. 이상과 같은 의림지 호저 퇴적층의 형성환경과 형성시기 연구를 통하여 의림지의 제방축조의 최초시기를 해석해 보면, 의림지의 제방은 적어도 과거 약 827년 전에서 866년 전에는 이미 축조되어 있었음을 알 수 있다. 과거 제천 일대에 살았던 옛사람들이 의림지 하류의 곡지중앙과 고기 충적선상지에 대한 관계용 용수조달의 필요성에 부응하여 상류부 곡지하천의 자연입지 환경을 최대한 이용하여 축조한 것으로 판단된다..준비하였다.전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다.se that were all low

• Economic and Environmental Geology
• /
• v.45 no.3
• /
• pp.317-333
• /
• 2012

The Yeongweol Group is a Lower Paleozoic mixed carbonate-siliciclastic sequence in the Taebaeksan Basin of Korea, and consists of five lithologic formations: Sambangsan, Machari, Wagok, Mungok, and Yeongheung in ascending order. Sequence stratigraphic interpretation of the group indicates that initial flooding in the Yeongweol area of the Taebaeksan Basin resulted in basal siliciclastic-dominated sequences of the Sambangsan Formation during the Middle Cambrian. The accelerated sea-level rise in the late Middle to early Late Cambrian generated a mixed carbonate-siliciclastic slope or deep ramp sequence of shale, grainstone and breccia intercalations, representing the lower part of the Machari Formation. The continued rise of sea level in the Late Cambrian made substantial accommodation space and activated subtidal carbonate factory, forming carbonate-dominated subtidal platform sequence in the middle and upper parts of the Machari Formation. The overlying Wagok Formation might originally be a ramp carbonate sequence of subtidal ribbon carbonates and marls with conglomerates, deposited during the normal rise of relative sea level in the late Late Cambrian. The formation was affected by unstable dolomitization shortly after the deposition during the relative sea-level fall in the latest Cambrian or earliest Ordovician. Subsequently, it was extensively dolomitized under the deep burial diagenetic condition. During the Early Ordovician (Tremadocian), global transgression (viz. Sauk) was continued, and subtidal ramp deposition was sustained in the Yeongweol platform, forming the Mungok Formation. The formation is overlain by the peritidal carbonates of the Yeongheung Formation, and is stacked by cyclic sedimentation during the Early to Middle Ordovician (Arenigian to Caradocian). The lithologic change from subtidal ramp to peritidal facies is preserved at the uppermost part of the Mungok Formation. The transition between Sauk and Tippecanoe sequences is recognized within the middle part of the Yeongheung Formation as a minimum accommodation zone. The global eustatic fall in the earliest Middle Ordovician and the ensuing rise of relative sea level during the Darrwillian to Caradocian produced broadly-prograding peritidal carbonates of shallowing-upward cyclic successions within the Yeongheung Formation. The reconstructed relative sea-level curve of the Yeongweol platform is very similar to that of the Taebaek platform. This reveals that the Yeongweol platform experienced same tectonic movements with the Taebaek platform, and consequently that both platform sequences might be located in a body or somewhere separately in the margin of the North China platform. The significant differences in lithologic and stratigraphic successions imply that the Yeongweol platform was much far from the Taebaek platform and not associated with the Taebaek platform as a single depositional system. The Yeongweol platform was probably located in relatively open shallow marine environments, whereas the Taebaek platform was a part of the restricted embayments. During the late Paleozoic to early Mesozoic amalgamations of the Korean massifs, the Yeongweol platform was probably pushed against the Taebaek platform by the complex movement, forming fragmented platform sequences of the Taebaeksan Basin.

• Journal of the Korean earth science society
• /
• v.40 no.1
• /
• pp.24-36
• /
• 2019

In the mid-eastern Yellow Sea, glacio-eustatic sea-level fluctuations and a regional tectonic subsidence have combined to represent an aggradational stacking pattern of sedimentary units during late Pleistocene-Holocene. The accumulated sediments are divisible into two-type units of Type-A and Type-B in high-resolution air-gun seismic profiles and the deep-drilled core of YSDP-105. Type-A unit largely comprises clast-rich coarse-grained sediments of non-marine to paralic origin, whereas Type-B unit consists mostly of tidal fine-grained sediments. Based on a bottom model of the sedimentary units, this study suggested a geoacoustic model of long-coring bottom layers at the YSDP-105 drilling site of the mid-eastern Yellow Sea. The geoacoustic model of 64-m depth below the seafloor with four-layer geoacoustic units was reconstructed in continental shelf strata at 45 m in water depth. For actual modeling, the geoacoustic property values of the models were compensated to in situ depth values below the seafloor using the Hamilton modeling method. We suggest that the geoacoustic model will be used for geoacoustic and underwater acoustic experiments of mid- and low-frequency reflecting on the deep bottom layers in the mid-eastern Yellow Sea.