• 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.

• 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.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.1 s.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.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.61-70
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• 2006

3-D S-wave velocity model in the southern Korean Peninsula is investigated by using the joint inversion of receiver functions and surface-wave dispersion. A peninsula average Rayleigh-wave phase velocity in the 10-150 seconds range and tomographic estimates of the Rayleigh and Love wave group velocities in the 0.5-20 seconds period range determined using a $12.5{\times}12.5\;km$ grid for the southern part of the peninsula are used for the inversion. Receiver functions were determined from broadband (STS-2), short-period (SS-1) and acceleration (Episensor) channels of 95 stations. The dense distribution of the stations in the Peninsula permits us to examine the 3-D crustal structure in detail. The inversion result shows the variation and characteristics of S-wave velocity in the crust and upper mantle of the southern Korean Peninsula very well.

• 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.

• Economic and Environmental Geology
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• v.56 no.3
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• pp.277-291
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• 2023

To analyze the crustal velocity structures beneath 21 broadband seismic stations in Gangwon Province, South Korea, we first applied the H-κ stacking method to 139 teleseismic event data (Mw ≥ 5.8 and the epicentral distance of 30° - 90°) occurring between March 18, 2019 and December 31, 2022 to estimate the Moho depths and V_p/V_s ratios beneath each station. The Moho depths and V_p/V_s ratios from the H-κ stacking method range from 24.9 to 33.2 km depth and 1.695 - 1.760, respectively, and the estimated V_p/V_s ratios were applied to the joint inversion of receiver functions and surface wave dispersion to obtain 1-D crustal velocity models beneath each station. The resulting Moho depths range from 25.9 to 33.7 km depth, similar to the results from the H-κ stacking method. Moho depth results from the both methods are generally consistent with Airy's isostasy. The 1-D crustal velocity models confirm that the existence of 2 km thick low-velocity layers with P-wave velocities of 5 km/s or less at some stations in the Taebaeksan basin, and at the stations CHNB and GAPB in northern Gangwon Province, which are located above the Cenozoic sedimentary layer. The station SH2B, although not overlying a sedimentary layer, has a low P-wave velocity near the surface, which is probably due to various factors such as weathering of the bedrock. We also observe a velocity inversion with decreasing velocity with depth at all stations within 4 - 12 km depths, and mid-crustal discontinuities possibly due to density differences in the rocks at around 10 km depth below some stations.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.66-73
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• 2014

To estimate the shear-velocity ($v_s$) structure beneath the WIZ station on White Island in New Zealand, we applied receiver function (RF) inversion and H-${\kappa}$ stacking methods to 362 teleseismic events (Mw > 5.5) recorded during April 20, 2007 to September 6, 2013. Using 71 RFs with errors less than 20% after 200 iterative computations, we determined that the depth to Moho of $v_s$ = 4.35 km/s is $24{\pm}1km$ within a 15 km radius of the station. In an 1-d $v_s$ model derived by RF inversions, a 4-km thick low-velocity layer (LVL) at depths of 18 ~ 22 km was identified in the lower crust. This LVL, which is 0.15 km/s slower than the rocks above and below it, may indicate the presence of a deep magma reservoir. The H-${\kappa}$ stacking method yielded an estimate of the depth to the Moho of 24.5 km, which agrees well with the depth determined by RF inversions. The low $v_p/v_s$ ratio of 1.64 may be due to the presence of gas-filled rock or hot crystallizing magma.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.18-26
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• 2013

Shear-wave velocity ($v_s$) structures beneath two seismic stations, JJU and JJB on the flanks of the volcano Halla on Jeju island, Korea, were estimated by receiver-function inversion and H-${\kappa}$ stacking applied to 150 teleseismic events ($M_W{\geq}5.5$) recorded since 2007. $P_S$ waves converted at the Moho discontinuity does not appear clearly for northwesterly back-azimuths ($207{\sim}409^{\circ}$, average $308^{\circ}$) at station JJU and southeasterly back-azimuths ($119{\sim}207^{\circ}C$, average $163^{\circ}$) at station JJB. This may be due to a gradual velocity increase at Moho or heterogeneity within the crust. The $v_s$ models derived by inversion of receiver functions indicate a distinct low velocity layer ($v_s{\leq}3.5km/s$; LVL) within the crust and a gradual increase in $v_s$ in the depth interval of 30 to 40 km. Within the radius of 18 km beneath station JJB, the LVL occurs at depths of 14 ~ 26 km and the 'Moho' ($v_s{\geq}4.3km/s$) is at 34 km depth. Ten kilometers to the west, within the radius of 16 km beneath station JJU, both the LVL and the Moho are significantly shallower, at depths of 14 to 24 km and 30 km, respectively. H-${\kappa}$ analyses for stations JJU and JJB yield estimated crustal thickness of 29 and 33 km and $v_p/v_s$ ratios of 1.64 and 1.75, respectively. The lesser $v_p/v_s$ ratio was derived for rocks nearest to th peak of the volcano.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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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.

• 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.