• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.225-231
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• 2000

The crystallographic and magnetic properties of the sample F $e_{0.8}$ $Co_{0.18}$(BN)$_{0.02}$ synthesized by microwave arc-melting with the maximum power of 3.5 kW have been studied by the methods of an X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in a form of pellet pressed under the pressure of 9,000 N/c $m^2$, rolled coldly, and treated with the different temperatures. The X-ray diffraction pattern of pelleted sample shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The X-ray diffraction pattern shows that a residual stress, which exists in the sample, is eliminated by final 90$0^{\circ}C$ annealing. As rolling rate and heat treatment temperature increases, the saturation magnetization and the remanence of the samples increase whereas the coercivity of the samples shows decrease. Also the saturation magnetization and the remanence of the samples were affected by rolling rate and rolling direction than heat treatment temperature, but the coercivity of the samples was affected by rolling rate and direction as well as heat treatment temperature. This means that a domain wall motion is easy due to elimination of a residual stress and an inclusion which exists in the sample by rolling and heat treatment and a local induced-magnetization easy axis was also formed to parallel to the rolling direction due to creation of the like-atom pairs across the slip plane by rolling......

• Economic and Environmental Geology
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• v.54 no.6
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• pp.615-627
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• 2021

The Baekildo fault, a dextral strike-slip fault developed in Baekil Island, Goheung-gun, controls the distribution of tuffaceous sandstone and lapilli tuff and shows a complex fracture system around it. In this study, we examined the spatial variation in the geometry and connectivity of the fracture system by using circular sampling and topological analysis based on a detailed fracture trace map. As a result, both intensity and connectivity of the fracture system are higher in tuffaceous sandstone than in lapilli tuff. Furthermore, the degree of the orientation dispersion, intensity, and average length of fracture sets vary depending on the along-strike variation in structural position in the tuffaceous sandstone. Notably, curved fractures abutting the fault at a high angle occur at a fault bend. Based on the detailed observation and analyses of the fracture system, we conclude as follows: (1) the high intensity of the fracture system in the tuffaceous sandstone is caused by the higher content of brittle minerals such as quartz and feldspar. (2) the connectivity of the fracture system gets higher with the increase in the diversity and average length of the fracture sets. Finally, (3) the fault bend with geometric irregularity is interpreted to concentrate and disturb the local stress leading to the curved fractures abutting the fault at a high angle. This contribution will provide important insight into various geologic and structural factors that control the development of fracture systems around faults.

• 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.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.509-515
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• 2009

Three earthquakes with local magnitude ($M_L$) greater than 3.0 occurred on April 24, June 2 and September 12 in 1999 nearby the Gyeongju area. Redetermined epicenters were located within the radius of 1 km. We carried out waveform inversion analysis to estimate focal mechanism of June 2 event, and P and S wave polarity and their amplitude ratio analysis to estimate focal mechanisms of April 24 and September 12 events. June 2 and September 12 events had similar fault plane solutions each other. The fault plane solution of April 24 event included those of other 2 events, but its distribution range was relatively broad. Focal mechanisms of those events had a strike slip faulting with a small normal component. P-axes of those events were ENE-WSW which were similar to previous studies on the P-axis of the Korean Peninsula. Considering distances between epicenters, similarities of seismic waves and sameness of polarities of seismic data recorded at common seismic stations, these events might occurred at the same fault. The seismic moment of June 2 event was estimated to be $3.9\;{\times}\;10^{14}\;N{\cdot}m$ and this value corresponded to the moment magnitude ($M_W$) 3.7. The moment magnitude estimated by spectral analysis was 3.8, which was similar to that estimated by waveform inversion analysis. The average stress drop was estimated to be 7.5 MPa. Moment magnitudes of April 24 and September 12 events were estimated to be 3.2 and 3.4 by comparing the spectrum of those events recorded at common single seismic station.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.353-363
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• 1999

The Cretaceous and the Upper Jurassic strata of the Korean Peninsula, entirely of continental facies, form a sedimentary mega-unit subdivided into three unconformity-bounded units. The lower, Upper Jurassic-early Lower Cretaceous unit (Jasong Synthem) occurs profusely in North Korea and is characterized by volcanic rocks of intermediate to acidic, calc-alkaline to alkaline compositions; but strata of this unit is very rare in South Korea. The middle, Hauterivian-Lower Albian unit occurs commonly in the Korean Peninsula, but some alkalinesubalkaline basalt and andesite occur only in South Korea. A recently obtained U-Pb isochron age about 113.6 Ma (Chang et at, 1998) from the zircon grains of the Kusandong Tuff in the uppermost part of the Haman Formation has thrown much light on the age of this unit. The stratotype of this Hauterivian-L. Albian unit is the Sindong and Hayang Groups of the Kyongsang Basin, where the unit is about twice thick and has more conglomerates than in sedimentary basins in North Korea. The unit shows various sedimentary cycles in different basins showing that the cyclicity is controlled by local crustal motion. The upper, Upper Albian-Upper Cretaceous unit is abundant in South Korea with prolific volcanic rocks which are intermediate to acidic and notably calc-alkaline. In North Korea, however, this unit occurs in only one locality without volcanic rocks and is not voluminous. The distribution of these three unconformity-bounded units shows a stepwise younging toward the Pacific Ocean: the lower unit occurs mainly in N Korea, the middle unit occurs in both N and S Korea, and the upper unit occurs mainly in the southern part of S Korea. The Cretaceous sedimentary basins of S Korea were genetically controlled by paralleling sinistral strike-slip faults parallel to the Pacific margin.

• Journal of Yeungnam Medical Science
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• v.2 no.1
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• pp.11-22
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• 1985

Femur neck fracture is well known as one of the major death cause after trauma in elderly patients, and unsolved fracture due to its frequent association with complications such as avascular necrosis and nonunion. Through meticulous evaluation of the patient, hip and surgeon's experiences, reduction of mortality and morbidity as well as rapid recovery of the patient to the preinjury social and ambulatory status without local complications and revision after treatment is urgently needed. Many factors about this fracture In itself were noted, but we have analyzed 18 femur neck fractures of the patients older than 50 years preliminarily according to age, fracture pattern, osteoporosis, etiology and method of treatment with its delay in association with major complications especially avascular necrosis and nonunion. The results are as follows; 1. Of these 18 fractures, 11 were in females, 8 were caused by minor trauma such as slip-down accident and 4 were associated with definite osteoporosis according to the Sing's classification. 2. Fracture pattern of these 18 are undisplaced in 4, displaced subcapital in 11, displaced transcervical in 3. 11 fractures in the patients older than 60 year are composed of 3 undisplaced or impacted fractures and 8 displaced subcapital fractures. 3. These 18 fractures were treated by closed reduction and Internal fixation with multiple pins in 13, and hemiarthroplasty in 4, but one was not treated to die after discharge from hospital. 4. 4 undisplaced or impacted fractures and 3 displaced transcervical fractures were not associated with any complications such as avascular necrosis or nonunion. But 4 of 6 displaced subcapital fractures were complicated by avascular necrosis, 3 of which were reduced in the varus position within 1 week, and the other was reduced in the good position on 1 week after trauma. There was no complication in 2 displaced subcapital fractures reduced in valgus position within 3 days after trauma. According to the above results, the prognosis of the femur neck fracture is dependent upon the fracture pattern and delay in its treatment. So it is inevitable to reduce the fracture in anatomical or valgus position as early as possible. But the arthroplasty may be needed in displaced subcapital fractures delayed for several days, with its reluction in extreme varus position or impossible and with pre-existing disease in the same hip Joint (total hip replacement).