• Journal of the Korean Geophysical Society
• /
• v.2 no.2
• /
• pp.123-134
• /
• 1999

Magnetotelluric responses may be affected by strong anisotropy of the high-conductivity layers (HCL) in the upper mantle or lower crust. We have studied two-dimensional anisotropy MT modelling to examine the effect of high anisotropic media. Electrical properties of a homogeneous anisotropic body are defined by a symmetric conductivity tensor and the problem is described by coupled diffusion equation in the frequency domain. In two-dimensional anisotropic environments, diagonal elements of the impedance tensor have higher values than those in isotropic environments. In some cases, TM mode phases reach more than 90°and apparent resistivities decrease for some frequency range because of telluric distortion. GB decomposition may be used to recover regional responses, but can be affected by the regional anisotropic effect. Considering these results, BC87 dataset was interpreted with a modified anisotropic model.

• Journal of the Korean Geophysical Society
• /
• v.4 no.1
• /
• pp.21-33
• /
• 2001

Simultaneous inversion of first-arrivals of local earthquakes recorded by the Korea Meteorological Administration(KMA) seismograph network from 1991 to 1998 is made to derive 1D crustal velocity structure of the Korean peninsula. Twenty-nine events with 178 observations are used in the inversion. Average crustal P-wave velocity turns out to be about 6.3 km/sec, and crustal thickness and upper mantle P-wave velocity are estimated as 33 km and 7.9 km/sec, respectively. Results of inversion indicate the possibility of the low velocity layer in the lower crust. Joint inversion is applied to estimate hypocenters, station delays, and velocities simultaneously. Relative station corrections for 11 stations range from zero to about 1.2 sec. Analysis of the synthetic data shows that estimates of hypocenter locations and station corrections as well as averaged crustal structure are reliable for the given data set..

• Journal of the Korean earth science society
• /
• v.21 no.3
• /
• pp.349-358
• /
• 2000

Compressional and shear wave velocities (Vp and Vs) and densities have been measured for serpentinite, amphibolite, amphibole and biotite schist, and gneiss from western part of Chungnam Province at room temperature. Ranges of the density are 2.6${\sim}$2.86g/cm$^3$ for serpentinite, 2.25${\sim}$2.81g/cm$^3$ for talc, and 2.74${\sim}$3.07g/cm$^3$ for metamorphic rocks. Of these rocks, talc shows wider ranges than serpentinite and amphibolites due to its metamorphic process from serpentinite. Values of Vp and Vs are 5719${\sim}$6062m/s and 2898${\sim}$3351m/s for serpentinites, 4019${\sim}$5478m/s and 2241/${\sim}$2976m/s for talc, 5375${\sim}$6372m/s and 3042${\sim}$3625m/s for amphibolite, 5290${\sim}$5499m/s and 2968${\sim}$3137m/s for schist, and 4788m/s and 2804m/s for gneiss, respectively. Velocity of P wave increases 1.47 times faster than S wave with increase of density. The results of seismic velocity measurement show anisotropy, higher velocity across than along the schistocity of rocks, especially in metamorphic rocks. This fact indicates that there were regional metamorphism related with tectonic forces. Values of seismic velocity increase with increasing pressure from 20 MPa to 70 MPa, especially in metamorphic rocks. Overall recalculated Vp and Vs values suggest that the serpentinite indicates for upper mantle in the respects of seismic characteristics, in spite of high degree of serpentinization. In addition, those of the amphibolite do for low crust, and gneiss and schist for upper crust.

• Journal of the Korean earth science society
• /
• v.30 no.2
• /
• pp.153-164
• /
• 2009

We examined the regional 1-D deep resistivity structure of the Korean Peninsula using MT data acquired at seven sites located in the Kyongsang Basin and Kyonggi Massif. At the sites located in the Kyongsang Basin, surrounding sea distorts observed MT response and hence this distortion, so called "sea effect", is corrected using an iterative tensor stripping method. The 1-D layered inversion results for the seven MT sites reveal 4 layered structure, which is composed of 1) near surface layer, 2) upper crust, 3) lower crust and upper mantle, and 4) asthenosphere from the surface downward. Conrad interface, which is a boundary between upper and lower crust, is distinctly identified beneath all the MT sites. Conrad interface depth is estimated to about be 17km in the Kyongsang Basin and about 12km in the Kyonggi Massif, while the upper crust of the Kyongsang Basin is about 5 times more resistive than that of the Kyonggi Massif. Finally, asthenosphere is inferred to exist below a depth of approximately 100km with a resistivity of 200-300 ohm-m.

• Journal of the Mineralogical Society of Korea
• /
• v.31 no.3
• /
• pp.161-172
• /
• 2018

Multi-anvil press (MAP) is one of the high pressure apparatuses and often generates the pressure-conditions ranging from 5 to 25 GPa and temperature-conditions up to $2,300^{\circ}C$. The MAP is, therefore, suitable to explore the pressure-induced structural changes in diverse earth materials from Earth's mantle and the bottom of the mantle transition zone (~660 km). In this study, we present the experimental results for pressure-load calibration of the 1,100-ton multi-anvil press equipped in the authors' laboratory. The pressure-load calibration experiments were performed for the 14/8 step, 14/8 G2, 14/8 HT, and 18/12 assembly sets. The high pressure experiments using ${\alpha}$-quartz, wollastonitestructure of $CaGeO_3$, and forsterite as starting materials were analyzed by powder X-ray diffraction spectroscopy. The phase transition of each mineral indicates the specific pressure that is loaded to a sample at $1,200^{\circ}C$: a transition of ${\alpha}$-quartz to coesite at 3.1 GPa, that of garnet-structure of $CaGeO_3$ to perovskite-structure at 5.9 GPa, that of coesite to stishovite at 9.2 GPa, and that of forsterite to wadsleyite at 13.6 GPa. While the estimated pressure-load calibration curve is generally consistent with those obtained in other laboratories, the deviation up to 50 tons is observed at high pressure above 10 GPa. This is partly because of the loss of oil pressure at high pressure resulting from the differences in a sample chamber, and the frictional force between pressure medium and second anvil. We also report the ${\sim}200^{\circ}C/mm$ of thermal gradient in the vertical direction of the sample chamber of 14/8 HT assembly. The pressure-load calibration curve and the observed thermal gradient within the sample chamber can be applied to explain the structural changes and the relevant macroscopic properties of diverse crystalline and amorphous earth materials in the mantle.

• Geophysics and Geophysical Exploration
• /
• v.13 no.3
• /
• pp.256-267
• /
• 2010

Earthquakes in the Korean Peninsula occur along the faults formed and boundaries between major geological units ruptured due to violent tectonic activities during the Mesozoic. E-W and/or ENE-SSW compressive stress regime resulting from collisions between the Eurasian plate and neighbouring the Indian plate, the Pacific plate and the Philippine plate trigger Korean earthquakes of thrust faulting with predominant strike-slip components along the mostly NNE-SSW trending active faults. Seismicity of the Korean peninsula has been moderate to low during the past 20 centuries except for the period from the 15th to the 18th centuries of exceptionally high seismicity, showing the typical irregularity of intraplate seismicity. The structure of the Korean peninsula is rather homogeneous without the Conrad discontinuity sharply dividing the upper and lower crust. Lateral heterogeneities exist in the crust. The crust with an average thickness of about 33 km is thicker in the mountainous region than the plain due to the Airy-type isostatic equilibrium maintained in the peninsula. Crustal P-wave velocity with average of about 6.3 km/sec increases gradually from the near surface to the Moho. The upper mantle P-wave (Pn) velocity is about 7.8 km/sec.

• Economic and Environmental Geology
• /
• v.30 no.5
• /
• pp.477-491
• /
• 1997

In the Bibong area of the western part of Chungcheongnam-do, ultramafic masses occur as discontinuous isolated lenticular bodies in the Precambrian Kyeonggi gneiss complex. They extend for about 200 m long to NNE directions which are parallel to fault lines in the gneiss complex. The ultramafic masses contact with the adjacent gneiss complex as steeply dipping faults. They are dunites and harzburgites and many of them are partially or completely serpentinized. The ultramafic rocks dominantly show protogranular, equigranular and equigranular-$m{\grave{o}}saic$ textures. They also show porphyroclastic (megacrystic) or recrystallized textures reflecting several stages of metamorphism. They contain varying amounts of olivine $(Fo_{89-92})$, enstatitic to bronzitic orthopyroxene, diopsidic clinopyroxene, tremolitic to pargasitic hornblende, and spinel with serpentine, talc, chlorite, calcite and magnetite. The ultramafic rocks have high magnesium numbers and transitional element contents, low alkali contents and show deplete REE patterns. Comparing with available data, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to those of worldwide mantle xenoliths and orogenic related ultramafic rocks. The field evidences, petrographical, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to alpine type ultramafic rocks emplaced into the crust by the faulting as mantle slab types. With the petrographical characteristics, these mineralogical compositions suggest that the ultramafic rocks of the Bibong area have experienced several stages of retrogressive metamorphism in a condition ranging from the upper amphibolite facies to greenschist facies.

• Geophysics and Geophysical Exploration
• /
• v.6 no.1
• /
• pp.40-52
• /
• 2003

Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into the adjacent Ulleung Basin from multichannel seismic reflection and ocean bottom seismometer data. The Ulleung Basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal. The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the margin is characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under the slope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced during continental rifting In response to high upper mantle temperature. The acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Korean margin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin.

• Radiation Oncology Journal
• /
• v.16 no.2
• /
• pp.147-157
• /
• 1998

Purpose : The aim of this retrospective study is to assess the necessity of s1aging laparotomy in the management of supradiaphragmatic CS I-II Hodgkin's disease. Prognostic factors and the usefulness of prognostic factor groups were also analyzed. Materials and Methods : From 1985 to 1995, fifty one Patients who were diagnosed as supradiaphragmatic CS I-II Hodgkin's disease at Yonsei Cancer Center in Seoul, Korea were enrolled in this study Age range was 4 to 67 with median age of 30. The number of patients with each CS IA, II A, and IIB were 16, 25, and 10, respectively. Radiotherapy(RT) was delivered using 4 or 6 MV photon beam to a total dose of 19.5 to 55.6Gy (median dose : 45Gy) with a 1.5 to 1.BGy per fraction. Chemotherapy(CT) was given in 2-12 cycles(median : 6 cycles). Thirty one Patients were treated with RT alone, 4 patients with CT alone and 16 patients with combined chemoradiotherapy. RT volumes varied from involved fields(3), subtotal nodal fields(18) or mantle fields(26). Results : Five-year disease-free survival rate(DFS) was $78.0\%$ and overall survival rate(05) was $87.6\%$. Fifty Patients achieved a complete remission after initial treatment and 8 patients were relapsed. Salvage therapy was given to 7 patients, 1 with RT alone, 4 with CT alone, 2 with RT+CT. Only two patients were successfully salvaged. Feminine gender and large media-stinal adenopathy were significant adverse prognostic factors in the univariate analysis for DFS. The significant adverse prognostic factors of OS were B symptom and clinical stage. When patients were analyzed according to European Organization for Research and Treatment of Cancer(EORTC) prognostic factor groups, the DFS in Patients with very favorable, favorable and unfavorable group was 100, 100 and $55.8\%$(p<0.05), and the 05 in each patients' group was 100, 100 and $75.1\%$(p<0.05), respectively. In very favorable and favorable groups, the DFS and 05 were all $100\%$ by RT alone, but in unfavorable group, RT with CT had a lesser relapse rate than RT alone. The subtotal nodal irradiation had better OFS than mantle RT in patients treated with RT. Conclusion : In present study, the DFS and OS in patients who did not undergo s1aging laparotomy were similar with the results in the literatures of which patients were surgically staged. Therefore, we may suggest that staging laparotomy would not influence the outcome of treatments. In univariate analysis, gender, large mediastinal adenopathy. B symptoms and clinical stage were significant prognostic factors for the survival rate. We confirm the usefulness of EORTC prognostic factor groups which may be a good.

• Journal of the Korean earth science society
• /
• v.22 no.1
• /
• pp.20-29
• /
• 2001

P wave traveltime delays has been measured and a preliminary tomouaphic inversion has been performed using the data collected from the network deployed by Korea National University of Education in the southcentral part Korea. The maximum variation in relative traveltime residuals is almost 0.7 seconds. A large azimuthal variation in traveltime residuals is observed at the stations in the northwestern part of the study area. This might indicate the existence of lateral velocity heterogeneity beneath the study area. Although, the inverted tomographic image seems to be correlated with the tectonic boundary between Kyunggi Massif and Okcheon Belt, the confidence level is presently low. We should place on the importance of this study for finding preferable inversion parameters and predicting probable result. Better tomographic image of the study area can be obtained in the near future when the data are accumulated.