• The Journal of the Petrological Society of Korea
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• v.25 no.1
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• pp.85-88
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• 2016

The new rocks of the oceanic crust, like basalt, are created in the mid-oceanic ridge, and the magnetic polarities of the rocks are supposed to be oriented as following the Earth's magnetic field. An extensive magnetic survey of total field at sea level reveals mainly unusual north-south magnetic stripes parallel to the axis of the mid-oceanic ridge, especially in the Atlantic Ocean. From this stripes the Earth's magnetic field is considered as repeatedly 'flipped'(the N pole becoming the S pole, and vice versa) and many times over geological time. The discovery of stripes of alternately normal and reversed-magnetized rocks forming the ocean floor has been a key evidence for the sea-floor spreading, continental drift, and plate tectonics. This study introduces a simple apparatus to explain a possible mechanism of the magnetic reversal in the new oceanic crust, which makes a magnetic stripe adjacent to the mid-oceanic ridge. The apparatus shows a bar magnet effect of adjoined stripes to have a special magnetic polarity on the rocks in the center of the mid-oceanic ridge. The new magnetic stripe seems to be generated not only by Earth's magnetic field, but also by neighbored stripes in the mid-oceanic ridge, acting as a bar magnet.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.189-197
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• 2006

The Korea Plateau is a continental fragment rifted and partially segmented from the Korean Peninsulaat the initial stage of the opening of the East Sea (Japan Sea). We interpreted marine seismic profiles from the South Korea Plateau in conjunction with swath bathymetric to investigate processes of con-tjnental rifting and separation of the southwestern Japan Arc. The SouU-i Korea Plateau preserves funda-mental elements of rift architecture comprising a seaward succession of a rift basin and an uplifted rift flank passing into the slope, typical of a passive continental margin. Two distinguished rift basins (Onnuri and Bandal Basins) in the South Korea Plateau are bounded by major synthetic and smaller antithetic faults, creating wide and symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. Rifting was primarily controlled by normal faulting resulting from extension orthogonal to the inferred line of breakup along the base ofthe slope rather U-ian strike-slip deformation. Two extension direcdons for rifdng are recog-nized; U-ie Onnuri Basin was rifted in U-ie EW direction; U-ie Bandal Basin in U-ie EW and NW-SE directions, suggesting two rift stages. We interpret that the E-W direction represents initial rifting at the inner margin; while the Japan Basin widened, rifting propagated repeatedly from the Japan Basin to the southeast toward the Korean margin but could not penetrate the strong continental lithosphere of the Korean Shield and changed direction to the south, resulting in E-W extension to create the rift basins at the Korean margin. The Hupo Basin to the south of the Korea Plateau is estimated to have formed in this process. The NW-SE direction probably represents the direction of rifting orthogonal to the inferred line of breakup along the base of the slope of the South Korea Plateau; after breakup the southwestern Japan Arc separated in the SE direction, indicating a response to tensional tectonics associated with the subduction of the Pacific Plate in the NE direction. We suggest that structural evolution of the eastern Korean margin can be explained by the processes occurring at the passive continental margin.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.1-6
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• 2005

Analogue physical modelling using granular materials (i.e., sandbox experiments) has been applied with great success to a number of geological problems at various scales. Such physical experiments can also be simulated numerically with the Discrete Element Method (DEM). In this study, we apply the DEM simulation to the collision between the Indian subcontinent and the Eurasian Plate, one of the most significant current tectonic processes in the Earth. DEM simulation has been applied to various kinds of dynamic modelling, not only in structural geology but also in soil mechanics, rock mechanics, and the like. As the target of the investigation is assumed to be an assembly of many tiny particles, DEM simulation makes it possible to treat an object with large and discontinuous deformations. However, in DEM simulations, we often encounter difficulties when we examine the validity of the input parameters, since little is known about the relationship between the input parameters for each particle and the properties of the whole assembly. Therefore, in our previous studies (Yamada et al.,2002a,2002b,2002c), we were obliged to tune the input parameters by trial and error. To overcome these difficulties, we introduce a numerical biaxial test with the DEM simulation. Using the results of this numerical test, we examine the validity of the input parameters used in the collision model. The resulting collision model is quite similar to the real deformation observed in eastern Asia, and compares well with GPS data and in-situ stress data in eastern Asia.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.1
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• pp.30-48
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• 2019

The year 2018 is the $50^{th}$ anniversary of scientific ocean drilling. Nevertheless, we know more about the surface of the moon than the Earth's ocean floor. In other words, there are still no much informations about the Earth interior. Much of what we do know has come from the scientific ocean drilling, providing the systematic collection of core samples from the deep seabed. This revolutionary process began 50 years ago, when the drilling vessel Glomar Challenger sailed into the Gulf of Mexico on August 11, 1968 on the first expedition of the federally funded Deep Sea Drilling Project (DSDP). DSDP followed successively by Ocean Drilling Program (ODP), Integrated Ocean Drilling Program (old IODP), and International Ocean Discovery Program (new IODP). Concerning on the results of scientific ocean drilling, there are two technological innovations and various scientific research results. The one is a dynamic positioning system, enables the drilling vessel to stay fixed in place while drilling and recovering cores in the deep water. Another is the finding of re-entry cone to replace drill bit during the drilling. In addition to technological innovation, there are important scientific results such as confirmation of plate tectonics, reconstruction of earth's history, and finding of life within sediments. New IODP has begun in October, 2013 and will continue till 2023. IODP member countries are preparing for the IODP science plan beyond 2023 and future 50 years of scientific ocean drilling. We as IODP member also need to participate in keeping with the international trend.

• Geophysics and Geophysical Exploration
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• v.27 no.2
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• pp.119-128
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• 2024

Marine magnetic surveys provide a rapid and cost-effective method for pioneer geophysical survey for many purposes. Sea-surface magnetometers offer high accuracy but are limited to measuring the scalar total magnetic field and require dedicated cruise missions. Shipboard three-component magnetometers, on the other hand, can collect vector three components and applicable to any cruise missions. However, correcting for the ship's magnetic field, particularly viscous magnetization, still remains a challenge. This study proposes a new additional correction method for ship's viscous magnetization effect in vector data acquired by shipboard three-component magnetometer. This method utilizes magnetic data collected simultaneously with a sea-surface magnetometer providing total magnetic field measurements. Our method significantly reduces deviations between the two datasets, resulting in corrected vector anomalies with errors as low as 7-25 nT. These tiny errors are possibly caused by the vector magnetic anomaly and its related viscous magnetization. This method is expected to significantly improve the accuracy of shipborne magnetic surveys by providing corrected vector components. This will enhance magnetic interpretations and might be useful for understanding plate tectonics, geological structures, hydrothermal deposits, and more.

• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.369-384
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• 2006

Korean Peninsula, located on the southeastern part of Eurasian plate, belongs to the intraplate region. The characteristics of intraplate earthquake show the low and rare seismicity and the sparse and irregular distribution of epicenters comparing to interplate earthquake. To evaluate the exact seismic activity in intraplate region, long-term seismic data including historical earthquake data should be archived. Fortunately the long-term historical earthquake records about 2,000 years are available in Korea Peninsula. By the analysis of this historical and instrumental earthquake data, seismic activity was very high in 16-18 centuries and is more active at the Yellow sea area than East sea area. Comparing to the high seismic activity of the north-eastern China in 16-18 centuries, it is inferred that seismic activity in two regions shows close relationship. Also general trend of epicenter distribution shows the SE-NW direction. In Korea Peninsula, the first seismic station was installed at Incheon in 1905 and 5 additional seismic stations were installed till 1943. There was no seismic station from 1945 to 1962, but a World Wide Standardized Seismograph was installed at Seoul in 1963. In 1990, Korean Meteorological Adminstration(KMA) had established centralized modem seismic network in real-time, consisted of 12 stations. After that time, many institutes tried to expand their own seismic networks in Korea Peninsula. Now KMA operates 35 velocity-type seismic stations and 75 accelerometers and Korea Institute of Geoscience and Mineral Resources operates 32 and 16 stations, respectively. Korea Institute of Nuclear Safety and Korea Electric Power Research Institute operate 4 and 13 stations, consisted of velocity-type and accelerometer. In and around the Korean Peninsula, 27 intraplate earthquake mechanisms since 1936 were analyzed to understand the regional stress orientation and tectonics. These earthquakes are largest ones in this century and may represent the characteristics of earthquake in this region. Focal mechanism of these earthquakes show predominant strike-slip faulting with small amount of thrust components. The average P-axis is almost horizontal ENE-WSW. In north-eastern China, strike-slip faulting is dominant and nearly horizontal average P-axis in ENE-WSW is very similar with the Korean Peninsula. On the other hand, in the eastern part of East Sea, thrust faulting is dominant and average P-axis is horizontal with ESE-WNW. This indicate that not only the subducting Pacific Plate in east but also the indenting Indian Plate controls earthquake mechanism in the far east of the Eurasian Plate. Crustal velocity model is very important to determine the hypocenters of the local earthquakes. But the crust model in and around Korean Peninsula is not clear till now, because the sufficient seismic data could not accumulated. To solve this problem, reflection and refraction seismic survey and seismic wave analysis method were simultaneously applied to two long cross-section traversing the southern Korean Peninsula since 2002. This survey should be continuously conducted.

• Economic and Environmental Geology
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• v.44 no.1
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• pp.83-94
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• 2011

Extra heavy oil reservoirs are distributed over the world but most of them is deposited in the northern part of the Orinoco River in Venezuela, in the area of 5,500 $km^2$, This region, which has been commonly called "the Orinoco Oil Belt", contains estimated 1.3 trillion barrels of original oil-in-place and 250 billion barrels of established reserves. The Venezuela extra heavy oil has an API gravity of less than 10 degree and in situ viscosity of 5,000 cP at reservoir condition. Although the presence of extra heavy oil in the Orinoco Oil Belt has been initially reported in the 1930's, the commercial development using in situ cold production started in the 1990's. The Orinoco heavy oil deposits are clustered into 4 development areas, Boyaco, Junin, Ayachoco, and Carabobo respectively, and they are subdivided into totally 31 production blocks. Nowadays, PDVSA (Petr$\'{o}$leos de Venzuela, S.A.) makes a development of each production block with the international oil companies from more than 20 countries forming a international joint-venture company. The Eastern Venezuela Basin, the Orinoco Oil Belt is included in, is one of the major oil-bearing sedimentary basins in Venezuela and is first formed as a passive margin basin by the Jurassic tectonic plate motion. The major source rock of heavy oil is the late Cretaceous calcareous shale in the central Eastern Venezuela Basin. Hydrocarbon materials migrated an average of 150 km up dip to the southern margin of the basin. During the migration, lighter fractions in the hydrocarbon were removed by biodegradation and the oil changed into heavy and/or extra heavy oil. Miocene Oficina Formation, the main extra heavy oil reservoir, is the unconsolidated sand and shale alternation formed in fluvial-estuarine environment and also has irregularly a large number of the Cenozoic faults induced by basin subsidence and tectonics. Because Oficina Formation has not only complex lithology distribution but also irregular geology structure, geological evolution and characteristics of the reservoirs have to be determined for economical production well design and effective oil recovery. This study introduces geological formation and evolution of the Venezuela extra heavy oil reservoirs and suggest their significant geological characteristics which are (1) thickness and geometry of reservoir pay sands, (2) continuity and thickness of mud beds, (3) geometry of faults, (4) depth and geothermal character of reservoir, (5) in-situ stress field of reservoir, and (6) chemical composition of extra heavy oil. Newly developed exploration techniques, such as 3-D seismic survey and LWD (logging while drilling), can be expected as powerful methods to recognize the geological reservoir characteristics in the Orinoco Oil Belt.