• Title/Summary/Keyword: 하부지각

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수신함수를 이용한 한반도내의 광대역관측소부근의 속도구조 연구 (1)

  • 박윤경;전정수;김성균
    • Proceedings of the KSEEG Conference
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    • 2003.04a
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    • pp.139-142
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    • 2003
  • 지구물리학적 연구에서 있어서 가장 중요한 목적 중의 하나는 지각과 상부 맨틀의 상세한 구조를 규명하는 것이다. 3성분의 지진기록을 이용하여 관측소 하부의 지각구조를 연구하는 몇 가지 방법들이 개발되었으며, 수신함수분석(receiver function analysis)이 가장 널리 사용되고 있다 (Phinney, 1964: Burdick and Langston, 1977: Owens and Crosson, 1988). 수신함수는 원거리 지진의 P파와 관측소 하부의 Moho면에서 전환된 Ps 전환파를 이용하여 관측소 하부의 지각구조를 계산하는 것이다. (중략)

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The Applicability of Seismic Waves to Detect a Low Velocity Body of the Geothermal Area (지열부지의 저속도층을 탐지하기 위한 지진파의 응용성)

  • 김소구
    • The Journal of Engineering Geology
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    • v.4 no.3
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    • pp.333-341
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    • 1994
  • The low velocity body was detected during the invesfigation of the crustal structune and upper mantle in the Korean Peninsula using ray method and observational seismic data. We observed the arrival time delays of P and S waves that pass through the Bugok hot spring area and the chugaryong rift zone in the Korean Peninsula. The present geothermal exploration accounts for the high heat flow in these regions, suggesting that the area are the 'delay shadows' produced by a deep, low velocity body(Resenberg et aL, 1980). We tried to verify the hypothesis that the low-velocity body is caused by the partial melting in the lower crust can be explained by the lateral variation(inhomogeneous model) of the lower crust velocity using Ray Method(Cerveny and Psencik, 1983).

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Crustal Structure of the Continental Margin of Korea in the East Sea: Results From Deep Seismic Sounding (한반도의 동해 대륙주변부의 지각구조 : 심부 탄성파탐사결과)

  • Kim Han-Joon;Cho Hyun-Moo;Jou Hyeong-Tae;Hong Jong-Kuk;Yoo Hai-Soo;Baag Chang-Eop
    • Geophysics and Geophysical Exploration
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    • v.6 no.1
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    • pp.40-52
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    • 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.

Crustal Structure under the Taejon(TJN) Station by Receiver Function Methods

  • Yu, Hyeon-Je;Lee, Gi-Hwa
    • Journal of the Korean Geophysical Society
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    • v.4 no.1
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    • pp.35-46
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    • 2001
  • 한반도 중부에 위치한 대전 지진관측소(TJN) 하부의 세부 지각구조를 밝혀내기 위하여 수신함수를 이용한 선형화된 역산(linearized inversion) 방법을 적용하였다. 본 방법의 비단일해(nonuniqueness)와 초기 모델 의존성의 문제를 해결하기 위해 근사 초기 속도 모델로부터 72개의 서로 다른 초기 모델을 구하여 역산을 수행한 후 결과모델들의 평균 속도 모델을 제시하는 방법을 사용하였다. 역산 결과 총 72개의 모델 중 뚜렷한 지각-맨틀 경계를 보이는 43개의 모델만이 조건에 만족하는 결과를 나타내었다. 모든 모델에서 속도 구조는 전체적으로 깊이에 따라 속도의 불연속면이나 급격한 증가없이 연속적인 변화를 하며, 모호면의 깊이는 30~32.5 km의 범위로 나타났다. 평균적인 하부 지각의 속도는 6.5 km/s, 상부 맨틀의 속도는 7.8 km/s로 뚜렷한 속도 변화를 보였다. 결과 모델 군은 중부지각(mid-crust)에서의 속도를 기준으로 약한 저속도층을 나타내는 군과 상대적으로 일정한 속도를 가지는 군으로 구분되었다. 단지 지진파형의 비교만으로 두 모델군 중 합당한 모델군의 선택은 불가능하였다. 따라서 수신 함수를 이용하여 연구 지역의 신뢰할 만한 지각 구조를 구하기 위해서는 그 지역에 대한 지질학적, 지구물리학적 추가정보와의 동반 해석이 요구된다.

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Geochemical Composition of the Continental Crust in Korean Peninsula (한반도 지각암류의 지구화학적 특성)

  • Lee, Seung-Gu;Kim, Dong-Yeon
    • The Journal of the Petrological Society of Korea
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    • v.21 no.2
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    • pp.113-128
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    • 2012
  • The chemical composition of the continental crust play an important role in understanding of crustal formation and evolution and quantifying other processes taking place within continental crust. We summarized geochemical data reported in the previous literature for the crustal rocks in the Korean Peninsula and divided their chemical composition into geologic time scale. In the variation diagram normalized by average composition of the upper crustal rocks, the geochemical characteristics of the upper crust during Triassic period is different from those of the upper crustal rocks after Jurassic period or before Precambrian. However, the geochemical characteristics of the Jurassic and Precambrian period are similar each other. Our summarized data indicate that the source material of Triassic upper crust may be different from that of Jurassic or Precambrian upper crust.

Fluid Inclusions Trapped in Xenoliths from the Lower Crust/upper Mantle Beneath Jeju Island (I): A Preliminary Study (제주도의 하부지각/상부맨틀 기원의 포획암에 포획된 유체포유물: 예비연구)

  • Yang, Kyounghee
    • The Journal of the Petrological Society of Korea
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    • v.13 no.1
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    • pp.34-45
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    • 2004
  • This paper describes the textural relations of mantle xenoliths and fluid inclusions in mantle-derived rocks found in alkaline basalts from Jeju Island which contain abundant ultramafic, felsic, and cumulate xenoliths. Most of the ultramafic xenoliths are spinel-lherzolites, composed of olivine, orthopyroxene, clinopyroxene and spinel. The felsic xenoliths considered as partially molten buchites consist of quartz and plagioclase with black veinlets, which are the product of ultrahigh-temperature metamorphism of lower crustal materials. The cumulate xenoliths, clinopyroxene-rich or clinopyroxene megacrysts, are also present. Textural examination of these xenoliths reveals that the xenoliths are typically coarse grained with metamorphic characteristics, testifying to a complex history of evolution of the lower crust/upper mantle source region. The ultramafic xenoliths contain protogranular, porphyroclastic and equigranular textures with annealing features, indicating the presence of shear regime in upper mantle of the Island. The preferential associations of spinel and olivine with large orthopyroxenes suggest a previous high temperature equilibrium in the high-Al field and the original rock-type was a Al-rich orthopyroxene-bearing peridotite without garnet. Three types of fluid inclusions trapped in mantle-derived xenoliths include CO$_2$-rich fluid (Type I), multiphase silicate melt (glass ${\pm}$ devitrified crystals ${\pm}$ one or more daughter crystals + one or more vapor bubbles) (Type II), and sulfide (melt) inclusions (Type III). C$_2$-rich inclusions are the most abundant volatile species in mantle xenoliths, supporting the presence of a separate CO$_2$-rich phase. These CO$_2$-rich inclusions are spatially associated with silicate and sulfide melts, suggesting immiscibility between them. Most multiphase silicate melt inclusions contain considerable amount of silicic glass. reflecting the formation of silicic melts in the lower crust/upper mantle. Combining fluid and melt inclusion data with conventional petrological and geochemical information will help to constrain the fluid regime, fluid-melt-mineral interaction processes in the mantle of the Korean Peninsula and pressure-temperature history of the host xenoliths in future studies.

Receiver Function Inversion Beneath Ngauruhoe Volcano, New Zealand, using the Genetic Algorithm (유전자 알고리즘을 이용한 뉴질랜드 Ngauruhoe 화산 하부의 수신함수 역산)

  • Park, Iseul;Kim, Ki Young
    • Geophysics and Geophysical Exploration
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    • v.18 no.1
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    • pp.1-8
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    • 2015
  • To estimate the shear-wave velocity (${\nu}_s$ beneath the OTVZ seismic station on Ngauruhoe volcano in New Zealand, we calculated receiver functions (RFs) using 127 teleseismic data ($Mw{\geq}5.5$) with high signal-to-noise ratios recorded during November 11, 2011 to September 11, 2013. The genetic inversion algorithms was applied to 21 RFs calculated by the iterative time-domain deconvolution method. In the 1-D ${\nu}_s$ model derived by the inversion, the Moho is observed at a 14 km depth, marked by a ${\nu}_s$ transition from 3.7 km/s to 4.7 km/s. The average ${\nu}_s$ of the overlying crust is 3.4 km/s, and the average ${\nu}_s$ of a greater than 9-km thick low-velocity layer (LVL) in the lower crust is 3.1 km/s. The LVL becomes thinner with increasing distance from the station. Another LVL thicker than 10 km with ${\nu}_s$ less than 4.3 km/s is found in the upper mantle. Those LVLs in the lower crust and the upper mantle and the relatively thin crust might be related to the magma activity caused by the subducting Pacific plate.

Two-dimensional Inversion of Sea-effect-corrected Magnetotelluric (MT) Data in Jeju Island (해양효과가 보정된 제주도 자기지전류 탐사 자료의 2차원 역산)

  • Yang, Jun-Mo;Lee, Heui-Soon;Lee, Choon-Ki;Park, Gye-Soon
    • Journal of the Korean earth science society
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    • v.32 no.6
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    • pp.602-612
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    • 2011
  • Jeju Island, a volcanic island located in South Korea, has been one of the main targets of geophysical and/or geological studies because of its tectonic importance related to the volcanism and tectonic link to the southern part of the Korean Peninsula. Recently, as a number of broad-band magnetotelluric (MT) measurements were made, we have examined the deep part of the island. In such an insular setting, it is not easy to properly recover the deep structures such as the lower crust and the upper crust using MT data, because their low-frequency components are strongly affected by the surrounding sea of the island. In this study, we apply the sea-effect correction to the existing MT data collected at a total of 102 sites in Jeju Island. The sea-effect correction makes remarkable changes in the observed MT data at frequencies below 1 Hz, clearly indicating the existence of a conductive lower crust. The 2-D inversion results for both Jeju Southern Line (JSL) and Jeju Northern Line (JNL) show that the transition zone separating the resistive upper crust and conductive lower crust exists at a depth of 20 km on average.

Testing of risk perception survey - Diabetes mellitus in Korea (당뇨병 위험 지각 측정 도구의 타당성 평가)

  • Kang, Soo Jin
    • Journal of the Korean Data and Information Science Society
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    • v.27 no.2
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    • pp.477-486
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    • 2016
  • This study was to evaluate of the reliability and validity of the Risk Perception Survey - Diabetes Mellitus (RPS-DM) with Korean diabetes patients. A total of 183 patients participated in this study from December 4, 2014 to January 1, 2015 with self-reported questionnaires. The data was analyzed using exploratory factor analysis, cronbach's alpha, and item to total correlation. The factor structure of the instrument showed the cumulative variance of 45.1% in the factor analysis and a four-factor structure was found to be appropriate. The comparative site risk score matched with the RPS-DM in English except item 7, 8, and 12. The RPS-DM in Korean version has been found to be reliable and valid.