• Title, Summary, Keyword: 한반도의 지각구조

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3-D Crustal Velocity Tomography in the Southern Part of The Korean Peninsula (한반도 남부지역의 3-D 속도 토모그래피)

  • Kim, So Gu;Li, Qinghe
    • Economic and Environmental Geology
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    • v.31 no.2
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    • pp.127-139
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    • 1998
  • A new technique of simultaneous inversion for 3-D seismic velocity structure by using direct, reflected, and refracted waves is applied to the southeast part of the Korean Peninsula including Pohang Basin, Kyongsang Basin and Ryongnam Massif. Pg, Sg, PmP, SmS, Pn, and Sn arrival times of 44 events with 554 seismic rays are inverted for locations and crustal structure. $6{\times}6$ with $0.5^{\circ}$ and 8 layers (4 km each layer) model was inverted. 3-D seismic crustal velocity tomography including eight sections from surface to Moho, ten profiles along latitude and longitude are analyzed. The results are as follows: 1) the average velocity and thickness of sediment are 5.04 km/s and 3-4 km, and the velocity of basement is 6.11 km/s. The shape of velocity in shallower layer is agreement with Bouguer gravity anomaly (Cho et al., 1997). 2) the velocities fluctuate strongly in the upper crust. The velocity distribution of the lower crust under Conrad appears basically horizontal. 3) the average depth of Moho is 30.4 km, and velocity is 8.01 km/s. 4) from the velocity and depth of the sediment, the thickness, velocity and form of the upper crust, and the depth and form of Moho, we can find the obvious differences among Ryongnam Massif, Kyongsang Basin and Pohang Basin. 5) the deep faults (a Ulsan series faults) near Kyongju and Pohang areas can be found to be normal and/or thrust faults with detachment extended to the bottom of the upper crust.

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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.

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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Study on the Geoelectrical Structure of the Upper Crust Using the Magnetotelluric Data Along a Transect Across the Korean Peninsula (한반도 횡단 자기지전류 탐사에 의한 상부 지각의 지전기적 구조 연구)

  • Lee, Choon-Ki;Kwon, Byung-Doo;Lee, Heui-Soon;Cho, In-Ky;Oh, Seok-Hoon;Song, Yoon-Ho;Lee, Tae-Jong
    • Journal of the Korean earth science society
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    • v.28 no.2
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    • pp.187-201
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    • 2007
  • The first magnetotelluric (MT) transect across the Korean Peninsula was obtained traversing from the East Sea shoreline to the Yellow Sea shoreline. The MT survey profile was designed perpendicular to the strike of the principal geologic structure of the Korean Peninsula $(N30^{\circ}E)$, so-called 'China direction'. MT data were achieved at 50 sites with spacings of $3{\sim}8km$ along the 240 km survey line. The impedance responses are divided into four subsets reflecting typical geological units: the Kyonggi Massif, the Okchon Belt, the western part of the Kyongsang Basin, and the eastern part of the Kyongsang Basin. In the western part of the Kyongsang Basin, the thickness of the sedimentary layer is estimated to be about 3 km to 8 km and its resistivity is a few hundred ohm-m. A highly conductive layer with a resistivity of 1 to 30 ohm-m was detected beneath the sedimentary layer. The MT data at the Okchon Belt show peculiar responses with phase exceeding $90^{\circ}$. This feature may be explained by an electrically anisotropic structure which is composed of a narrow anisotropic block and an anisotropic layer. The Kyonggi Massif and the eastern part of Kyongsang Basin play a role of window to the deep geoelectrical structure because of the very high resistivity of upper crust. The second layers with highest resistivities in 1-D conductivity models occupy the upper crust with thicknesses of 13 km in the Kyonggi Massif and 18 km in the eastern Kyongsang Basin, respectively.

On the isostasy and effective elastic thicness of the lithosphere in southern prt of the Korean Peninsula (한반도 남부 지각평형과 암석권의 유효탄성두께)

  • Choi, Kwang-Sun;Kim, Jeong-Hee;Shin, Young-Hong
    • Journal of the Korean Geophysical Society
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    • v.5 no.4
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    • pp.293-303
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    • 2002
  • Applying elastic plate model, we estimated elastic thickness and rigidity of the lithosphere in southern part of the Korean Peninsula($332km{\times}332km$ area of which center is $36.5^{\circ}N$ in latitude and $127.5^{\circ}E$ in longitude) by analysing terrain data and gravity data measured up to 2002. We tried to exclude the East Sea in choosing the study area because it has different tectonic environment. The mean Moho depth was estimated to be 30 km by power spectrum analysis of gravity data in the study area, Assuming one layer crust and applying elastic plate model, the loads with wavelengths of greater than 300 km are locally compensated, loads with wavelengths in the range 80-300km are partially supported by the strength of the lithosphere, and loads with wavelengths of less than 80km are almost completely supported by lithospheric strength. Assuming crustal model and rigidity, we calculated predicted coherence and compared it with observed coherence. As a result, we wert able to estimate the effective elastic thickness to be of 15 km(corresponding flexural rigidity is $3.0{\times}10^{22}Nm$). This indicates that the crust of the study area is relatively weaker than other old and stable continental regions but is similar to continental margins or oceanic area. The low rigidity could be explained by many tectonic and thermal activities such as orogenic activities, magmatic intrusions, volcanic activities, foldings, faultings, etc.

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Analysis of the Crustal Displacement at Yangsan Using Precise Point Positioning (정밀절대측위를 이용한 양산지역의 지각변위 해석)

  • Park, Joon-Kyu
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.28 no.2
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    • pp.289-295
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    • 2010
  • Yangsan fault system is a large fault more than 170km and one of the important structures Geologically that has been create recently in the Korean Peninsula. Debates have been made incessantly and widely throughout the Yangsan fault system because it's a lot of earthquake record. In this study, GPS data that was received from Yangsan GPS station in were processed by the Precise Point Positioning and the movement velocity was calculated by the statistical process about the results, where is the fault zone. The results showed that Yangsan is moving by azimuth angle of $126^{\circ}$ and the velocity of 49mm/year. It is respected that this results will be utilized in basic data about geophysics.

A study on the crustal structure of the continental margin in the East Sea along the Korea Peninsula using potential data (포텐셜자료를 이용한 한반도 동해 대륙주변부의 지각구조에 관한 연구)

  • Kim, Chang-Hwan;Yoo, Lee-Sun;Park, Chan-Hong;Suk, Dong-Woo
    • Journal of the Korean Geophysical Society
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    • v.10 no.1
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    • pp.13-25
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    • 2007
  • We investigated the undulation of Moho depth and the crustal structure of the continental margin in the East Sea along the Korea Peninsula from inversion and modelling using potential data and previous seismic results. Free-air gravity anomalies generally reflect topography effect. Bouguer gravity anomalies increase toward the Ulleung Basin, indicating that Moho depth is shallower under the Ulleung Basin. Positive magnetic anomalies exist along the continental margin and decrease toward the Ulleung Basin. In analytic signal, the small anomaly in the Hupo Bank infers that the Hupo Bank is uplifted by igneous intrusion and the strong anomaly on the continental slope denotes existence of SDR(seaward dipping reflectors), which are in accordance with the location of SDR detected in previous seismic studies. The inversion result of Bouguer gravity anomaly and the 2-dimensional gravity modelling indicate that the undulation of Moho depth shallows from the continental shelf toward the Ulleung Basin. This is in good agreement with the Moho depth calculated by the previous seismic velocity model using ocean bottom seismometer(OBS). The 2-dimensional gravity modelling infers magmatic underplating zone under the lower continental crust on the continental margin of the East Sea, indicating the possible rifiting of the continental margin.

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Preliminary Tomographic hversion for the Crustal Characteristics in the Central Region of South Korea (남한 중부지역의 지각특성 구명을 위한 토모그라피 역산에 의한 예비적 연구)

  • Lee, Duk-Kee;Kyung, Jai-Bok;Chung, Tae-Woong
    • Journal of the Korean earth science society
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    • v.22 no.1
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    • pp.20-29
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    • 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.

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Crustal structure of the Korean peninsula by inverting the travel times of first-arrivals from large explosions (대규모 발파자료 초동주시 역산을 통한 한반도 지각 속도구조 연구)

  • Kim Ki Young;Hong Myung Ho;Lee Jung Mo;Moon Woo Il;Baag Chang Eob;Jung Hee Ok
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.103-107
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    • 2005
  • In order to investigate the velocity structure of the southern part of the Korean peninsula, exploded seismic signals were recorded for 120 s along a 294-km WNW-ESE line and 150 s along a 335-km NNW-SSE line in 2002 and 2004, respectively. Velocity tomograms were derived from inverting first arrival times. One-dimensional velocity models derived by joint analyses of teleseismic receiver functions and surface wave dispersion at several stations near the profiles were uesd to build initial models. The raypaths indicate several midcrust interfaces including ones at approximate depths of 2.0 and 14.9 km with refraction velocities of approximately 6.0 and 7.1 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting velocity varies from 7.8 to 8.1 km/s along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at 6-7 km depth under the Okchon fold belt, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin whose thickness is less than 4.2 km.

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Crustal Structure of the Korean Peninsula by Inverting the Rravel Times of First-arrivals from Large Explosions (대규모 발파자료 초동주시 역산을 통한 한반도 지각 속도구조 연구)

  • Kim, Ki-Young;Hong, Myong-Ho;Lee, Jung-Mo;Moon, Woo-Il;Baag, Chang-Eob;Jung, Hee-Ok
    • Journal of the Korean Geophysical Society
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    • v.8 no.1
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    • pp.45-48
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    • 2005
  • In order to investigate the velocity structure of the southern part of the Korean peninsula, exploded seismic signals were recorded for 120 s along a 294-km WNW-ESE line and 150 s along a 335-km NNW-SSE line in 2002 and 2004, respectively. Velocity tomograms were derived from inverting first arrival times. One-dimensional velocity models derived by joint analyses of teleseismic receiver functions and surface wave dispersion at several stations near the profiles were uesd to build initial models. The raypaths indicate several midcrust interfaces including ones at approximate depths of 2.0 and 14.9 km with refraction velocities of approximately 6.0 and 7.1 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting velocity varies from 7.8 to 8.1 km/s along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at 6-7 km depth under the Okchon fold belt, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin whose thickness is less than 4.2 km.

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