• Economic and Environmental Geology
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• v.31 no.4
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• pp.339-347
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• 1998

The purpose of this study is to find P-wave crustal velocity structure and the Moho characteristics beneath Seoul (SEO) and Inchon (INCN) stations using broadband teleseismic records. The use of broadband receiver function analysis is increasing to estimate the fine-scale velocity structure of the lithosphere. The broadband receiver functions are developed from teleseismic events of P waveforms recorded at Seoul (SEO) and Inchon (INCN) stations, and are analyzed to examine the crustal structure beneath the stations. The teleseismic receiver functions are inverted in the time domain of the vertical P wave velocity structures beneath the stations. The crustal velocity structures beneath the stations are estimated using the receiver function inversion method (Ammon et al., 1990). The general features of inversion results are as follows: (1) For the Seoul station, the Conrad and Moho discontinuities exist at 22 km and 30 km depth in the south ($BAZ=180^{\circ}$) direction. (2) For the Inchon station, the Conrad discontinuity exists at 22 km depth in the direction of SE ($BAZ=145^{\circ}$) and the Moho discontinuity exists at 30~34 km depth with a 4 km thick, which consists of a laminated velocity transition layers with thickness, whereas a crust-mantle boundary beneath the Seoul station consists of a more sharp boundary compared with the Moho shape of INCN station.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.241-248
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• 2006

In this study, we applied the teleseismic receiver function technique to determine the crustal thicknesses and ratios for 31 broadband stations of the Korean Peninsula and map out the lateral variation of Moho depth in the Peninsula. The estimated depths to Moho range from 26 to 35 km except for an island station ULL (17 km). The Moho is turned out to be deeper in the south-western part of the Peninsula and western Gyeongsang basin, and shallower in the off-shore region close to East Sea (Sea of Japan). The ratio varies from 1.69 to 1.89 with the average of 1.77, which is close to global average (1.78) in the crust.

• Economic and Environmental Geology
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• v.36 no.3
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• pp.213-223
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• 2003

We estimated the Moho depth of Korean Peninsula from gravity anomalies and digital elevation model. The satellite radar altimetry-derived global free-air gravity model was used to ensure the homogeneity in both data and frequency domains of the original data. Two different methods were implemented to calculate the Moho depth; the wavenumber correlation analysis (Kim et al., 2000a) and the power spectrum analysis. The former method calculates depth-to-the-Moho by correlating topographic gravity effect with free-air gravity anomaly in the wavenumber domain under the assumption that the study area is not isostatically compensated. The latter one, on the other hand, considers the different density layers (i.e., Conrad and Moho), using complete Bouguer gravity anomaly in the Frequency domain of the Fourier transform. The correlation coefficient of the two Moho model is 0.53, and methodology and numerical error are mainly responsible for any mismatch between the two models. In order to integrate the two independentely-estimated models, we applied least-squares adjustment using the differenced depth. The resultant model has mean and standard deviation Moho depths of 32.0 km and 2.5 km with (min, max) depths of (20.3, 36.6) kms. Although this result does not include any topographic gravity effect, however, the validity of isostasy and the role of local stress field in the study area should be further studied.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.235-247
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• 1998

A new technique of simultaneons inversion for 3-D seismic velocity structure by using direct, reflected, and refracted waves is applied to the center of the Korean Peninsula including Pyongnam Basin, Kyonggi Massif, Okchon Fold Zone, Taebaeksan Fold Zone, Ryongnam Massif and Kyongsang Basin. Pg, Sg, PmP, SmS, Pn, and Sn arrival times of 32 events with 404 seismic rays are inverted for locations and crustal structure. 5 ($1^{\circ}$ along the latitude)${\times}6$ ($0.5^{\circ}$ along the longitude) ${\times}8$ block (4 km each layer) model was inverted. 3-D seismic crustal velocity tomography including eight sections from the surface to the Moho, eight profiles along latitude and longitude and the Moho depth distribution was determined. The results are as follows: (1) the average velocity and thickness of sediment are 5.15 km/sec and 3-4 km, and the velocity of basement is 6.12 km/sec. (2) the velocities fluctuate strongly in the upper crust, and the velocity distribution of the lower crust under Conrad appears basically horizontal. (3) the average depth of Moho is 29.8 km and velocity is 7.97 km/sec. (4) from the sedimentary depth and velocity, basement thickness and velocity, form of the upper crust, the Moho depth and form of the remarkable crustal velocity differences among Pyongnam Basin, Kyonggi Massif, Okchon Zone, Ryongnam Massif and Kyongsang Basin can be found. (5) The different crustal features of ocean and continent crust are obvious. (6) Some deep index of the Chugaryong Rift Zone can be located from the cross section profiles. (7) We note that there are big anisotropy bodies near north of Seoul and Hongsung in the upper crust, implying that they may be related to the Chugaryong Rift Zone and deep fault systems.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.589-592
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• 2005

Gravity characteristics and Moho undulations are investigated in the Korean peninsula by using satellite gravity data. According to the development of satellite geodesy, gravity potential models which have high accuracy and resolution were released. Using the EIGEN-CGOIC model based on low orbit satellite data such as CHAMP and GRACE, geoid and gravity anomaly were calculated by spherical harmonic analysis. The study area is located at $123^{\circ}\sim132^{\circ}E, 33^{\circ}\sim43^{\circ}$N including Korea. Free-air anomalies, which show the effect of terrain, have the values between $-37\sim724 mgal. After Bouguer correction, the range of simple Bouguer anomalies is $-221\sim246$ mgal. Complete Bouguer anomalies after terrain correction increase from continent to marine. This phenomenon is related rise of Moho discontinuity. The cut-frequency for extraction of Moho undulation was determined by power spectrum analysis, and then 3D inversion modeling was implemented. The mean, maximum, minimum, and standard deviation of Moho depth undulation are -26, -36, -8, and 4.9 krn, respectively.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.43-54
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• 2004

The 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 these stations. The teleseismic receiver functions are inverted in the time domain of the vertical P wave velocity structures beneath the stations. Clear P-to-S converted phases from the Moho interface are observed in teleseismic seismograms recorded at these stations. The crustal velocity structures beneath the stations are estimated by using the receiver function inversion method(Ammon et al., 1990). The general features of inversion results are as follows: (1) For the Inchon station, the Conrad discontinuity exists at 17.5 Km(SW) deep and the Moho discontinuity exists at 29.5 Km(NW) and 30.5 Km(SE, SW) deep. (2) The shallow crustal structure beneath Wonju station may be covered with a sedimentary rock of a 3 Km thickness. The average Moho depth is assumed about 33.0 Km, and the Conrad discontinuity may exist at 17.0 Km(NE) and 21.0 Km(NW) deep. (3) For Pohang station, the thickness of shallow sedimentary layer is a 3.0 Km in the direction of NE and NW. The Moho depth is 28.0 Km in the direction of the NE and NW. The Conrad discontinuity can be estimated to be existed at 21.0 Km deep for the NE and NW directions.

• 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.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.43-51
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• 2007

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 P-wave and S-wave first arrival times. The raypaths indicate several midcrust interfaces. The shallowest one is at the approximate depth of $2{\sim}3\;km$ with refraction velocities of approximately Vp=6.0 and Vs=3.5 km/s, respectively. The second one of $15{\sim}17\;km$ depth has refraction velocities of approximately Vp=7.1 and Vs=3.7 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting Vp of $7.8{\sim}8.1\;km/s$ and Vs of $4.2{\sim}4.6\;km/s$ along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at $6{\sim}7\;km$ depth under the Okchon fold belt and the Yeongnam massif, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin less than 4.2 km thick.

• 한국지구과학회:학술대회논문집
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• 2003.09a
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• pp.52-56
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• 2003

• Economic and Environmental Geology
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• v.44 no.6
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• pp.493-502
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• 2011

We study the deep structure of Korean Peninsula by estimating Moho depth and crustal thickness from using land and oceanic topography and free-air gravity anomaly data. Based on Airy-Heiskanen isostatic hypothesis, the correlated components between the terrain gravity effects and free-air gravity anomalies by wavenumber correlation analysis(WCA) are extracted to estimate the gravity effects that will be resulted from isostatic compensation for the area. With the resulting compensated gravity estimates, Moho depth that is a subsurface between the crust and mantle is estimated by the inversion in an iterative method with the constraints of 20 seismic depth estimates by the receiver function analysis, to minimize the uncertainty of non-uniqueness. Consequently, the average of the resulting crustal thickness estimate of Korean Peninsula is 32.15 km and the standard deviation is 3.12 km. Moho depth of South Korea estimated from this study is compared with the ones from the previous studies, showing they are approximately consistent. And the aspects of Moho undulation from the respective study are in common deep along Taebaek Mountains and Sobaek Mountains and low depth in Gyeongsang Basin relatively. Also, it is discussed that the terrain decorrelated free-air gravity anomalies inferring from the intracrustal characteristics of the crust are compared to the heat flow distributions of South Korea. The low-frequency components of terrain decorrelated Free-air gravity anomalies are highly correlated with the heat flow data, especially in the area of Gyeongsang basin where high heat flow causes to decrease the density of the rocks in the lower crust resulting in lowering the Moho depth by compensation. This result confirms that the high heat sources in this area coming from the upper mantle by Kim et al. (2008).