• Geomechanics and Engineering
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• v.30 no.3
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• pp.233-246
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• 2022

In this study, the city of Osijek is used as a case study area for low to medium seismicity regions with deep soil over deep geological deposits to determine horizontal PGA values. For this reason, we propose new regional attenuation equations for PGA that can simultaneously capture the effects of deep geology and local soil conditions. A micro-zoning map for the city of Osijek is constructed using the derived empirical scaling equations and compared to all prior seismic hazard estimates for the same area. The findings suggest that the deep soil atop deep geological sediments results in PGA values that are only 6 percent larger than those reported at rock soil sites atop geological rocks. Given the rarity of ground motion records for deep soils atop deep geological layers around the world, we believe this case study is a start toward defining more reliable PGA estimates for similar areas.

• The Korean Journal of Petroleum Geology
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• v.10 no.1_2 s.11
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• pp.34-39
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• 2004

This article discusses stratigraphy and geological history of continental shelf area covering of offshore San-in to Tsushima islands. Geological data from 5 wells and detailed seismic surveys indicate that sediments in the studied area are divided into 4 stratigraphic groups ranging from Oligocene to Tertiary in age, namely X, H, K, and D groups in ascending order. The oldest X group of Oligocene time comprises paralic sediments including volcanics deposited in the initial stage of basin-formation. N group of mainly lower Miocene time consists of deep marine sediment, representing the highest stage of transgression. Sediments of the K group of middle Miocene time show distinct off-lapping depositional pattern during the basinfilling stage. The youngest D group covers these older groups unconformably. Strong deformation of sediments prior to the deposition of the D group formed many anticlinal structures. Five exploratory wells were drilled at the selected structures, where only minor gas shows were encountered. The area provides the enough palaeotemperature to mature the source rocks at moderate depth.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.50-53
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• 2006

Regional geophysical surveys and geological cal studies on natural gas hydrate (NGH) in the East Sea were carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) from 2000 to 2004. 16 piston cores, 2270 L-km of multi-channel reflection seismic (MCRS) data and 730 L-km of 3.5kHz Chirp data obtained from the southwestern part of the deep-water Ulleung Basin were analyzed in this study. In piston cores, cracks generally developed parallel to bedding suggest significant gas content. The core analyses showed high total organic carbon (TOC) content, sedimentation rate and heat flow of sediments. These are in favor of the general ion of substantial biogenic methane, which can form the NGH within the stability zone of the near seafloor sediments in the study area. The cores generally show also high residual hydrocarbon gas concentrations for the formation of natural gas hydrates The geophysical indicators of the presence of gas and/or NGH such as bottom simulating reflectors (BSRs), seismic blank Bones, pockmarks and gas seeping features were well defined on the MCRS and Chirp data.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.145-150
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• 2005

A maximum of 3 km thickness of sediments were deposited above basement deformed by volcanic activities around the Dok Island. As the geological structure, the tension caused the basement-involved normal faults in the early stage of basin formation, whereas the sediment layers showed normal faults, volcanic domes and sills caused by volcanic activities. From the distribution of volcanics in order of age at the Ulleung Basin, volcanic activities were increased toward the northeastern direction (toward Dok Island). The study area is characterized by extensional crustal deformation before sediment deposition during the Early or Middle Miocene age, After the Late Miocene age, the basin was deformed by deep buried volcanics or subsidence of basin, in consequence, became complex geological structures.

• Journal of the Korean Geophysical Society
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• v.8 no.3
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• pp.131-135
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• 2005

A maximum of 3 km thickness of sediments were deposited above basement deformed by volcanic activities around the Dok Island. As the geological structure, the tension caused the basement-involved normal faults in the early stage of basin formation, whereas the sediment layers showed normal faults, volcanic domes and sills caused by volcanic activities. From the distribution of volcanics in order of age at the Ulleung Basin, volcanic activities were increased toward the northeastern direction(toward Dok Island). The study area is characterized by extensional crustal deformation before sediment deposition during the Early or Middle Miocene age. After the Late Miocene age, the basin was deformed by deep buried volcanics or subsidence of basin, in consequence, became complex geological structures.

• Journal of the Geological Society of Korea
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• v.54 no.5
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• pp.489-499
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• 2018

A series of geological events such as the formation of the Antarctic continental ice sheets, the changes in ocean circulation and a mass extinction after the onset of Oligocene has been studied as major concerns by various researches. However, paleoclimatic and paleoceanographic changes during the most period of Oligocene since the Eocene-Oligocene transition (EOT) still remains unclear. Especially, although the late Oligocene warming (LOW) has been assessed as the largest period in the paleoceanographic changes, the detailed understanding on the changed components is very low. The purpose of this study is the reconstruction of the paleoceanographic history during the late Oligocene using core sediments from IODP Expedition 342 Site U1406 performed in J-Anomaly Ridge in North Atlantic. Because North Atlantic deep water (NADW) has flowed southward through the study area since the early Oligocene, this area has been considered to an important location for studies on the changes of NADW. The core sediment analyzed in this study were deposited from about 26.0 to 26.5 Ma as evidenced by both of onboard and shore-based paleomagnetic data, and this is corresponded to the earliest period of LOW. The sediment profile can be divided into three Units (Unit 1, 2 & 3) based on the changes in both of total number and test size of Oridorsalis umbonatus as well as grain size data of clastic sediments. Unit 2 represents largest values in these three data. Because the total number, test size of O. umbonatus and grain size can be proxy records on the oxygen concentration and circulation intensity of deep water, we interpreted that Unit 2 had been deposited during the period of relatively strengthened NADW. Previous Cibicidoides spp. stable isotope results from the low latitude region of the North Atlantic also support our interpretation that is the intensified formation of NADW during the identical period. In conclusion, our results present a new evidence for the previous ideas that the causes on LOW are directly related to the changes in NADW.

• The Korean Journal of Petroleum Geology
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• v.6 no.1_2 s.7
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• pp.20-24
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• 1998

Expert system is one type of artificial intelligence softwares that incorporate problem-solving knowledges and experiences of human experts by use of symbolic reasoning and rules about a specific topic. In this study, an expert system, PLAYMAKER2, is used to interpret sedimentary facies and depositional settings of the sedimentary sequence. The original version of the expert system, PLAYMAKER, was developed in University of South Carolina in 1990, and modified into the present PLAYMAKER2 with some changes in the knowledge-base of the previous system. The late Cenozoic sedimentary sequence with maximum 10,000 m in thickness, which is located in the Korean Oil Exploration Block VI-1 at the southwestern margin of the Ulleung Basin, is analysed by the expert system, PLAYMAKER2. The Cenozoic sedimentary sequence is divided into two units-lower Miocene and upper Pliocene-Pleistocene sediments. The depositional settings and sedimentary facies of the Miocene sediments interpreted by PLAYMAKER2 in terms of belief values are: for depositional settings, slope; $57.4\%$, shelf; $21.4\%$, basin; $10.1\%$, and for sedimentary facies, submarine fan; $35.7\%$, continental slope; $26.3\%$, delta; $16.1\%$, deep basinplain; $6.1\%$ continental shelf; $3.2\%$, shelf margin; $1.4\%$. The depositional settings and sedimentary facies of the Pliocene-Pleistocene sediments in terms of belief values we: for depositional settings, slope; $59.0\%$, shelf; $22.8\%$, basin; $7.0\%$, and for sedimentary facies, delta; $24.1\%$, continental slope; $22.2\%$, submarine fan; $17.3\%$, continental shelf; $7.0\%$, deep basinplain; $4.8\%$, shelf margin; $2.6\%$. The comparison of the depositional settings and sedimentary facies consulted by PLAYMAKER2 with those of the classical interpretation from previous studies shows resonable similarity for the both sedimentary units-the lower Miocene sediments and the upper Pliocene-Pleistocene sediments. It demonstrates that PLAYMAKER2 is an efficient tool to interpret the depositional setting and sedimentary facies for sediments. However, to be a more reliable system, many sedimentologists should work to refine and add geological rules in the knowledge-base of the expert system, PLAYMAKER2.

• Journal of the Korean earth science society
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• v.35 no.2
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• pp.131-146
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• 2014

Multi-beam echosounder data and grain size analysis data of surface sediment were acquired and analyzed in order to investigate the shelf-to-slope morphology, geological character, and their geological controlling factors in the southwestern margin of the Ulleung Basin. According to the morphological character, the continental shelf can be divided into two parts: (1) shallow (~100 m) and steep ($0.5^{\circ}$) inner shelf, (2) deep (100-300 m) and gentle ($0.2^{\circ}$) outer shelf. The continental slope is featured with eight distinct topographic depressions of various spatial dimension (~121 $km^2$ in area) and head wall gradient (${\sim}24.3^{\circ}$). They are developed adjacent to each other and presumably formed by submarine landslides which have recurred under the strong influences of earthquakes and eustatic sea-level change. The inner continental shelf and the continental slope are dominated by fine-grained sediment, whereas the outer continental shelf is dominated by coarse-grained sediment. The surface sediment distribution seems dominantly influenced by eustatic sea-level change. The outer continental shelf is mostly covered by coarse relict sediment deposited during lowstand sea-level, while the inner shelf is covered with recent sediment during highstand sea-level. The surface of the continental slope is covered with fine-grained sediments which were supplied by hemipelagic advection process.

• Journal of the Korean Geophysical Society
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• v.9 no.4
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• pp.409-416
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• 2006

Reflection seismic survey has been conducted using R/V Yuzmogeologia of Russia on the area of between northern part of Powell basin and South Scotia Ridge. 48-channel seismic data have been processed using Promax system. Hesperides and Eastern Deep located in the central part of the South Scotia Ridge show similar geological structure comprising two distinct sedimentary layers. The lower layer filled with fault breccia is considered to be formed with the expansion of the deeps. The upper layer is filled with pelagic sediments which implies this layer is formed after the spreading of the deeps has stopped. The south branch of the South Scotia Ridge is characterized by bigger width than the north branch. Topographical depression shown in the south branch is formed by many faults accompanied with the seafloor expansion of Powell basin.

• Journal of the Mineralogical Society of Korea
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• v.5 no.1
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• pp.32-41
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• 1992

An XRD quantitative analytical method using calculated XRD patterns was discussed in this study, Deep-seabed sediments commonly contain smectite, illite, chlorite, and kaolinite, and XRD pattern of each clay mineral of appropriate chemical composition was simulated by using an XRD pattern calculation method. Theoretical peak intensities of specific reflections of four clay minerals (the 001 reflections of smectite and illite, the 004 reflection of chlorite, and the 002 reflection of kaolinite) were measured from calculated patterns, and MIF(mineral intensity factor)value of each phase was determined from the intensities of calculated patterns. The peak intensities obtaine from experimental XRD patterns of sediments were corrected using the MIF values so that the calibrated intensity values for the specimens are linearly proportional to the weight fraction of each phase, which is normalized to 100 wt%. The MIF method can provide accurate quantitaive results without the necessity of correcting the factors by the mass absorption coefficient of each phase. This method excludes the necessity of standard specimens having compositions that are similar to those of clay minerals in the sediment samples. Therefore, quantitaive analysis using XRD calculation method can be utilized for the specimens, for which the standard specimens are very difficult or impossible to obtain. this quantitative method can provide rapid, routine analysis results for a large number of samples which occur in similar geological environments.