• Title, Summary, Keyword: 한반도의 지각구조

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A Study of CHAMP Satellite Magnetic Anomalies in East Asia (동아시아지역에서의 CHAMP 위성자료에서의 지각 자기이상의 연구)

  • Kim, Hyung Rae
    • Economic and Environmental Geology
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    • v.54 no.1
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    • pp.117-126
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    • 2021
  • Satellite magnetic observations reflect the magnetic properties of deep crust about the depth of Curie isotherm that is a boundary where the magnetic nature of the rocks is disappeared, showing long wavelength anomalies that are not easily detected in near-surface data from airborne and shipborne surveys. For this reason, they are important not only in the analyses on such as plate reconstruction of tectonic boundaries and deep crustal structures, but in the studies of geothermal distribution in Antarctic and Greenland crust, related to global warming issue. It is a conventional method to compute the spherical harmonic coefficients from global coverage of satellite magnetic observations but it should be noted that inclusion of erroneous data from the equator and the poles where magnetic observations are highly disturbed might mislead the global model of the coefficients. Otherwise, the reduced anomaly model can be obtained with less corruption by choosing the area of interest with proper data processing to the area. In this study, I produced a satellite crustal magnetic anomaly map over East Asia (20° ~ 55°N, 108° ~ 150°E) centered on Korean Peninsula, from CHAMP satellite magnetic measurements about mean altitude of 280 km during the last year of the mission, and compared with the one from global crustal magnetic model (MF7). Also, a comparison was made with long wavelength anomalies from EMAG2 model compiled from all near-surface data over the globe.

Quaternary Tectonic Activities and Seismic Stability of Suryum Fault and Yupchon Fault, SE Korea (수렴단층과 읍천단층의 제4기 활동 및 지진 안정성)

  • Hwang, Sangill;Shin, Jaeryul;Yoon, Soon-Ock
    • Journal of the Korean association of regional geographers
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    • v.18 no.4
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    • pp.351-363
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    • 2012
  • Although the Korean peninsula has been considered as a largely aseismic region compared with the surrounding high seismic areas such as North China and Japan, there are more than thirty Quaternary faults reported so far, which are mostly centered in the southeastern peninsula. Structural studies of active faults exposed in Yangnam-myeon of Gyeongju, SE Korea are largely interpreted to post date the late Quaternary, suggesting that the NE-trending reverse faults may result from the active stress regime in the peninsula. The prevailing present-day E-W $S_{Hmax}$ orientations in the peninsula are consistent with the nature of plate forcing stemming from the convergence between the Indo-Australian and Eurasian plates. It is clear that the Quaternary faults have been reactivated, although resolving more elaborate time intervals responsible for a future rupture remains a significant challenge. This study contributes to better assess many of potential seismic hazards in the study area, in particular, in terms of seismic stability for foundation of nuclear power plant.

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Dynamics of Honeymoon and Statics of Structure: Changes and Continuity of Foreign Policy in the Moon Jae-In Administration (하니문의 동학(動學)과 구조의 정학(靜學): 문재인 정부의 외교정책, 변화와 연속성)

  • Choi, Jinwoo
    • Korean Journal of Legislative Studies
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    • v.24 no.2
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    • pp.5-38
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    • 2018
  • A seismic change is under way in diplomatic topography surrounding the Korean Peninsula. A new dynamic is being generated that could lead to a breakthrough in the nuclear stalemate and to an end of hostility between the two Koreas. Moon Administration's bold and creative foreign policy, which is alleged to place South Korea in the "driver's seat", is probably responsible for what is happening on the Korean Peninsula. However, on the other hand, Moon Administration's foreign policy shows a lot of continuity with foreign policy of previous conservative governments. In particular, the Moon government's emphasis on the vitality of the ROK-US alliance and its commitment to close coordination with the US in dealing with nuclear issues of North Korea is the hallmark of the continuity in South Korea's foreign policy. Emphasizing and sharing the notion of the continuities in foreign policy could contribute to social integration by garnering bi-partisan support. It could also spawn sense of stability, predictability, and confidence to diplomatic counterparts in other countries. And it could help avoid the negative effects of expectation-reality gap in the event that the outcome of all the diplomatic endeavor falls short of expectation held by citizens.

Crustal Structure of the Korean Peninsula from Broadband Teleseismic Records by Using Receiver Function (광대역 원격지진의 수신함수를 이용한 한반도 지각구조)

  • Kim, So Gu;Lee, Seoung Kyu;Jun, Myung soon;Kang, Ik Bum
    • Economic and Environmental Geology
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    • v.31 no.1
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    • pp.21-29
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    • 1998
  • Broadband receiver functions are developed from teleseismic P waveforms recorded at Wonju (KSRS), Inchon (IRIS), and Pohang (PHN), and are analyzed to examine the crustal structure beneath the three stations. The teleseismic receiver functions are inverted in the time domain to the vertical P wave velocity structure beneath the stations. Clear P-to-S converted phases from the Moho interface are observed in teleseismic seismograms recorded at the three stations. We estimated the crustal velocity structures beneath the stations using the receiver function inversion. The general features of inversion results are as follows: (1) For Pohang station, there is a high velocity gradient at a 4~5 km deep for SE and NW back azimuth and a low velocity zone at around 10 km deep. The Moho depth is 28 km for NW direction. (2) The shallow crustal structure beneath Wonju station is somewhat complex and there is a high-velocity zone ($V_p{\simeq}6.8km/sec$) at 3 to 4 km deep. The average crustal thickness is 33 km, and a transition zone exists at a 30~33 km deep of lower crust, of which velocity is abruptly changed 6.4 to 7.9 km/sec. (3) For Inchon station, the crustal velocity gradient monotonously increases up to the Moho discontinuity and the velocity is abruptly changed from 6.2 km/sec to 7.9 km/sec at 29 km deep.

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Moho Discontinuity Studies Beneath the Broadband Stations Using Receiver Functions in South Korea (수신함수를 이용한 남한의 광대역 관측망 하부의 Moho 불연속면 연구)

  • Kim, So-Gu;Lee, Seong-Kyu
    • Journal of the Korean Society of Hazard Mitigation
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    • v.1 no.1
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    • pp.139-155
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    • 2001
  • We investigate the vertical velocity models beneath the newly installed broadband seismic network of KMA (Korea Meteorological Administration) by using receiver function inversion technique. The seismic phases are primarily P-to-S conversions and reverberations generated at the two highest impedance interfaces like the Moho (crust-mantle boundary) and the sediment-basement contact. We obtained the teleseismic P-wave receiver functions, which were derived from teleseismic records of Seoul (SEO), Inchon (INCN), Tejeon (TEJ) , Sosan (SOS/SES), Kangnung (KAN), Ulchin (ULC/ULJ), Taegu (TAG), Pusan (PUS), and Ullung-do (ULL) stations. For Kwangju (KWA/KWJ) and Chunchon (CHU) stations, the Moho conversion Ps arrivals and waveforms of radial receiver functions are azimuthally inconsistent and unclear. From the receiver function inversion result, we found that crustal thickness is 29 km at INCN, SEO, and SOS (SES) stations, 28 km at KAN station in the Kyonggi Massif, 32 km at TEJ station in Okchon Folded Belt, 34 km at TAG, 33 km at PUS station in the Kyongsang Basin, 32 km at KWJ station (readjusted station by prior KWA station) included in the Youngdong-Kwangju Depression Zone, 28 km at ULC station in the eastern margin of the Ryongnam Massif, and 17 km at ULL station in the Ullung Island of the East Sea, respectively. The Moho configuration of INCN, SOS, KWJ, and KAN stations show a laminated smooth transition zone with a 3-5 km thick. The upper crusts(${\sim}5km$) of KAN, ULC, and PUS stations show complex structures with a high velocity. The unusually thick crusts are found at the TAG and PUS stations in the Kyongsang Basin compared to the thin (29-32 km) crust of the western part (INCN, SEO, SOS, TEJ, and KWA stations) The crustal thickness beneath Ullung Island (ULL station) shows the suboceanic crust with about 17 km thickness and complex with a high velocity layer of the upper crust, and the amplitudes of Incoming Ps waves from the western direction are relatively large compared to those from othor directions.

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Source Parameters for the 9 December 2000 $M_L$ 3.7 Offshore Yeongdeok Earthquake, South Korea (2000년 12월 9일 $M_L$ 3.7 영덕 해역 지진의 지진원 상수)

  • Choi, Ho-Seon
    • Geophysics and Geophysical Exploration
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    • v.13 no.2
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    • pp.137-143
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    • 2010
  • An earthquake with local magnitude $(M_L)$ 3.7 on December 9, 2000 occurred offshore Yeongdeok area, South Korea. In case of applying Chang and Baag (2006) crustal velocity model, the epicenter is $36.4462^{\circ}N\;and\;129.9789^{\circ}E$, which belongs to the inside of the Korean Peninsula Continental Shelf. Although we use the modified model reducing crustal thickness of Chang and Baag (2006) model by 5 km considering the transition from continental crust to oceanic crust in the East Sea, the epicenter was little changed. We carried out the waveform inversion analysis to estimate focal depth and focal mechanism of this event. The focal depth is estimated to be 11 ~ 12 km. The seismic moment is estimated to be $1.0{\times}10^{15}N{\cdot}m$, and this value corresponds to the moment magnitude $(M_W)$ 3.9. The offshore Yeongdeok event including May 29, 2004 offshore Uljin one show typical thrust faulting, and the direction of P-axis is ESE-WNW. The moment magnitude estimated by the spectral analysis is 4.0, which is similar to that by the waveform inversion analysis. Average stress drop is estimated to be 3.4 MPa.

Age and Structural Origin of the Tertiary Churyeong Breccia in the Gyeongju City, Korea (경주시 제3기 추령각력암의 퇴적시기와 구조적 성인)

  • Son, Moon;Kim, Seung-Hyun;Kim, Jong-Sun;Song, Cheol-Woo;Kim, In-Soo
    • The Journal of the Petrological Society of Korea
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    • v.18 no.2
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    • pp.137-151
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    • 2009
  • Synthetic analyses of field data, including rock facies, contact relationships, petrography, structural elements, and etc., and previous geochemical and absolute age data of the Tertiary Churyeong Breccia and its surrounding volcanics in the Gyeongju city, Korea, have led to the following results. (1) The Tertiary rocks are divided into the dacitic tuffs, Churyeong Breccia, and andesitic rocks in ascending order. The dacitic tuffs are unconformably overlain by the Churyeong Breccia which is intruded by or conformably overlain by the andesitic rocks. (2) The dacitic tuffs are correlated with the Paleocene${\sim}$Eocene Wangsan dacitic volcanics, while the Churyeong Breccia and andesitic rocks are correlated with the early Early Miocene Andongri Formation and Yongdongri Tuffs in the Waeup Basin, respectively. (3) The Churyeong Breccia accumulated rapidly in the NE-trending graben about 1.5 km in width during the crustal extension in the NW-SE direction due to the East Sea opening. (4) Dacitic${\sim}$andesitic volcanism and crustal extension were active during the early Early Miocene times in SE Korean peninsula. During the deposition the Churyeong Breccia, especially, the volcanism ceased for some time, but the active normal faulting led to the formation of grabens in places.

Moment Magnitude Determination Using P wave of Broadband Data (광대역 지진자료의 P파를 이용한 모멘트 규모 결정)

  • Hwang, Eui-Hong;Lee, Woo-Dong;Jo, Bong-Gon;Jo, Beom-Jun
    • Journal of the Korean Geophysical Society
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    • v.10 no.1
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    • pp.1-12
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    • 2007
  • A method to quickly estimate broadband moment magnitudes (Mwp) to warn regional and teleseismic tsunamigenic earthquakes is tested for application of the method to the different seismic observation environment. In this study, the Mwp is calculated by integrating far-field P-wave or pP-wave of vertical component of displacement seismograms in time domain from earthquakes, having magnitude greater than 5.0 and occurred in and around the Korean peninsula from 2000 to 2006. We carefully set up the size of the time window for the computations to exclude S wave phases and other phases following after the P wave phase. The P wave velocities and the densities from the averaged Korean crustal model are used in the computations. Instrumental correction was performed to remove dependency on the seismograph. The Mwp after the instrumental correction is about 0.1 greater than the Mwp before the correction. The comparison of our results to the those of foreign agencies such as JMA and Havard CMT catalogues shows a higher degree of similarity. Thus our results provide an effective tool to estimate the earthquake size, as well as to issue the necessary information to a tsunami warning system when the effective earthquake occurs around the peninsula.

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대규모 발파 후보지의 지하구조 학인을 위한 탄성파 굴절법 조사

  • Kim, Gi-Yeong;Kim, Dong-Hun
    • Journal of the Korean Geophysical Society
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    • v.5 no.2
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    • pp.153-161
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    • 2002
  • In order t determine blasting sites for the crustal refraction studies in the korean peninsula, seismic refraction profiling was conducted at two sites in the reclaimed land of Seosan. At a quarry for construction material and another site on a rice field 2km east of the quarry, 24 channel refraction profiling of 46m was conducted at a geophone spacing of 2m. Seismic velocity profiles obtained through tomographic invesion reveal that the quarry is regarded as an ideal place for blasting based on the observation that fresh basements with seismic velocities of 3,900 m/s or greater locate approximately 6m deep. On the contrary, under the reclaimed rice field, the basements are weathered more, of slower velocities, and buried deeper than quarry, indicating not an ideal location for detonating seismic explosives of large amounts.

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Geochemical Study of Dyke Swarms, SE Korea (한반도 남동부일원의 암맥군에 관한 지화학적 연구)

  • Kim, Jin-Seop;Kim, Jong-Sun;Son, Moon
    • The Journal of the Petrological Society of Korea
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    • v.11 no.3_4
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    • pp.182-199
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    • 2002
  • We attempted to show the evolution of the magma and the geochemical characteristics of dikes and dike swarms by using the petrographic and geochemical data from 287 dikes, SE Korea. The dikes can be divided into mafic, intermediate, and felsic dikes in the field. And each of them is subdivided into three groups, two groups, and two groups, respectively. The group (I) among the mafic dikes most pervasively occurs and are distributed in both sides of the Yeonil Tectonic Line (YIL), which petrographic and geochemical characteristics are the same. These facts thus, strongly support the results of the previous studies which showed that they were intruded contemporaneously and that YTL was a main tectonic line which restricted the crustal clockwise rotation during the Early Miocene. The geochemical characteristics are discriminated according to the seven groups divided petrographically. The mafic, intermediate and felsic dikes belong to basalt and basaltic andesite, andesite and facile, and rhyolite, respectively, and the magmas mostly belong to calc-alkaline series. The geochemical data indicate that there were the fractional crystallizations of olivine, clinopyroxene, and plagioclase in the mafic dikes. And the content of characteristic elements and tectonic discrimination diagrams show that the dikes were formed from the magma related to the subduction of plate and that the tectonic setting was related to orogenic volcanic arc.