• Journal of the Korean earth science society
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• v.30 no.1
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• pp.40-48
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• 2009

The attenuation mechanism of seismic waves in the crust is controlled both by intrinsic absorption and scattering of energy. The amount of scattering and intrinsic energy losses from the total attenuation is separately estimated in this study for the southern Korean Peninsula. The formula to be deduced from the theoretical relationship between single back-scattered coda Q and multiple scattering theory was used to separate the total attenuation into the intrinsic Q and the scattering Q. It was found that the intrinsic Q was considerably lower than that of the scattering Q in the frequency range of 1.5 to 20 Hz. This fact implies that the energy loss caused by the intrinsic absorption is relatively larger than one by the scattering effect within the crust of the southern Korean Peninsula. Both intrinsic and scattering Q values appeared to be comparatively larger than those measured in other seismically active regions except for intrinsic Q in the frequency range of 1.5 to 3 Hz.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.199-207
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• 2009

From 329 earthquake data in the Korean Peninsula, we separated the intrinsic and scattering quality factor ($Q_i^{-1}$ and $Q_s^{-1}$) using the Multiple Lapse Time Window Analysis (MLTW) method. For the homogeneous velocity structure, $Q_i^{-1}$ reduces the amplitudes of both direct and coda waves; $Q_s^{-1}$ diminishes the direct wave amplitude but enlarges the coda wave amplitude. Based on this phenomenon, MLTW method analytically derives theoretical curves and obtains $Q_i^{-1}$ and $Q_s^{-1}$ by least square fit with observation curves. This study is the first approach for the seismic stable region by MLTW method, and show that $Q_i^{-1}$ and $Q_s^{-1}$ in the Korean Peninsula are very low at lower than frequencies of 5 Hz. This low value seems to be related to the inactive tectonism of the Korean Peninsula.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.277-285
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• 2010

For regional earthquakes in the Korean Peninsula, the seismic Lg waves have the largest amplitude. Our researches in South Korea found that more reasonable low ${Q_{Lg}}^{-1}$ was obtained as the inter-station distances increase. The other methods such as coda normalization method and multiple lapse time window method also produced that the low ${Q_{Lg}}^{-1}$ is related to the values of seismically inactive region.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.97-100
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• 2008

Mount Fuji is the focus of intense study because of its potential hazard signaled by seismic, geologic and historical activity. Based on extensive seismic data recorded in the vicinity of Mt. Fuji, coda quality factor ($Q_c^{-1}$) using a single scattering model hypothesis, and intrinsic and scattering quality factor $(Q_i^{-1}$ and $Q_s^{-1})$ using the Multiple Lapse Time Window Analysis (MLTW) method was measured. To focus the study on the magmatic structure below Mt. Fuji, to the data were separated into two groups: a near-Fuji region of rays traversing an area with radius 5 km around the summit (R < 5 km), and a far-Fuji region of rays beyond a radius of 20 km around the summit (R > 20 km). The results of the study have a small error range due to the large data sample, showing that all $Q^{-1}$ values in near-Fuji area are greater than those of far-Fuji area, and $Q_i^{-1}$ for both the near and far-Fuji area is higher than $Q_s^{-1}$ at high frequencies. The $Q_i^{-1}$ values of the near-Fuji area are lower than those of the other volcanic areas considered, while values of $Q_s^{-1}$ are not. The low $Q_i^{-1}$ for the volcanic region of near-Fuji suggests that the magmatic activity, or percent of partial melt, at Mt. Fuji is not as active as hot spot volcanoes such as Kilauea, Hawaii.

• Journal of the Korean earth science society
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• v.24 no.8
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• pp.684-690
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• 2003

Recently Choongchung provinces in the central part of South Korea have received increasing attention because of the newly Planned administrative capital construction. In this area, a seismic network of Korea National University of Education has been installed since September 1996, and analyzed Q$_P^{-1}$ and Q$_S^{-1}$ by the extended Coda normalization method based on 60 events recorded by 2 stations of the network. To compensate for insufficient data, we combined the data from 33 events observed at 1 of the stations of the network of Korea Institute of Geology, Mining & Materials. Estimated Q$_P^{-1}$ and Q$_S^{-1}$ showed frequency dependence that decrease from (1.9${\pm}$3.0)${\times}$10$^{-3}$ and (2.4${\pm}$1.4)${\times}$10$^{-3}$ at 3.0 Hz to (5.4${\pm}$1.5)${\times}$10$^{-4}$ and (6.3${\pm}$1.1)${\times}$10$^{-4}$ at 24 Hz, respectively. Using a power law dependent on frequency, the best fit of Q$_P^{-1}$ and Q$_S^{-1}$ are 0.003f$^{-0.62}$ and 0.006f$^{-0.71}$ respectively. These values correspond to those of seismically stable regions, and are slightly less dependent on frequency than those of the southeastern part of Korea due to high Q$^{-1}$ values in high frequencies. Further observations are required in the central part of S. Korea to evaluate the difference of Q$^{-1}$ between central and southeastern parts of S. Korea.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.59-70
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• 2003

We estimated the spectrum decay parameter $\chi$ and the stress parameter ($\Delta$$\sigma$) in southeastern Korea. Especially, we propose a procedure to compute site-independent $\chi$$_{q}$ and dependent $\chi$$_{s}$ values, separately, This procedure is to use the coda normalization method for the computation of site independent Q or corresponding $\chi$$_{q}$ value as the first step followed by the next step, the computation of $\chi$$_{s}$ values for each site using the given $\chi$$_{q}$ value evaluated at the first step, For the estimation of stress parameter, we used seismic data monitored from three earthquakes occurred near Gyeongju in 1999 with the method of Jo and Baag, In addition, we simulated strong ground motion using the $\chi$ value and the stress parameter, In this case, we calculated the $\chi$ value with conventional method. The $\chi$ value of 0.016+0.000157R and the stress parameter of 92-bar was applied to the stochastic simulation, At last, we derived seismic attenuation equation using results of the stochastic prediction, and compared these results with some others reported previously.ported previously.

• Journal of the Korean earth science society
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• v.28 no.6
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• pp.720-732
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• 2007

For the Seoul metropolitan area and the eastern Kyeongsang Basin, we simultaneously calculated $Q_P^{-1}$ and $Q_S^{-1}$ by applying the extended coda-normalization method for 98 seismograms of local Earthquakes. As frequency increases from 1.5 Hz to 24 Hz, the result decreased from $(4.0{\pm}9.2){\times}10^{-3}$ to $(4.1{\pm}4.2){\times}10^{-4}$ for $Q_P^{-1}$ and $(5.5{\pm}5.6){\times}10^{-3}$ to $(3.4{\pm}1.3){\times}10^{-4}$ for $Q_S^{-1}$ in Seoul Metropolitan Area. The result of eastern Kyeongsang basin also decreased from $(5.4{\pm}8.8){\times}10^{-3}$ to $(3.7{\pm}3.4){\times}10^{-4}$ for $Q_P^{-1}$ and $(5.7{\pm}4.2){\times}10^{-3}$ to $(3.5{\pm}1.6){\times}10^{-4}$ for $Q_S^{-1}$. If we fit a frequency-dependent power law to the data, the best fits of $Q_P^{-1}$ and $Q_S^{-1}$ are $0.005f^{-0.89}$ and $0.004f^{-0.88}$ in Seoul metropolitan Area, respectively. The value of $Q_P^{-1}$ and $Q_S^{-1}$ in the eastern Kyeongsang basin are $0.007f^{-1.02}$ and $0.006f^{-0.99}$, respectively. The $Q_S^{-1}$ value of the eastern Kyeongsang basin is almost similar to Seoul metropolitan area. But the $Q_P^{-1}$ value of the eastern Kyeongsang basin is a little higher than that of Seoul metropolitan area. This may be that the crustal characteristics of the eastern Kyeongsang basin is seismologically more heterogeneous. However, these $Q_P^{-1}$ values in Korea belong to the range of seismically stable regions all over the world.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.19-27
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• 2001

Seismic parameters fur computation of ground motions in Southern Korea are obtained from recently recorded data, and site-independent regional and site-dependent local strong ground motions are predicted using efficient computational techniques. For the computation of ground motions, we devised an efficient procedure to compute site-independent $x_{q}$ and dependent $x_{s}$ values separately. The first step of this procedure is to use the coda normalization method far computation of site independent Q or corresponding $x_{q}$ value. The next step is the computation of $x_{s}$, values fur each site separately using the given $x_{q}$ value. For computation of ground motions the empirical Green's function (EGF) is modified to account fur the depth and distance variations of subevents on a finite fault plane using the theoritical Green's function. It is computed using wavenumber integration technique in layered media. The site dependent ground motions at seismic stations in southeastern local area were properly simulated using the modified empirical Green's function method in layered medium. The proposed method and procedures fur estimation of site dependent seismic parameters and ground motions could be efficiently used in the low and moderate seismicity regions.ons.s.ons.

• Journal of the Korean earth science society
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• v.27 no.4
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• pp.475-485
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• 2006

The physical properties of the central and southwestern crust of South Korea were estimated by comparing values of ${Q_P}^{-1}\;and\;{Q_S}^{-1}$ in the Kimcheon and Mokpo areas. In order to get ${Q_P}^{-1}\;and\;{Q_S}^{-1}$ values, seismic data were collected from two stations of the KIGAM network (KMC and MUN) and four stations of the KMA network (CPN, KUC, MOP, and WAN). An extended coda-normalization method was applied to these data. Estimates of ${Q_P}^{-1}\;and\;{Q_S}^{-1}$ show variations depending on frequency. As frequencies vary from 3 Hz to 24 Hz, the estimates decrease from $(1.4{\pm}3.9){\times}10^{-3}\;to\;(2.3{\pm}3.5){\times}10^{-4}\;for\;{Q_P}^{-1}\;and\;(1.8{\pm}1.3){\times}10^{-3}\;to\;(1.9{\pm}1.5){\times}10^{-4}\;for\;{Q_S}^{-1}$ in central South Korea, and $(5.9{\pm}4.8){\times}10^{-3}\;to\;(2.2{\pm}3.8){\times}10^{-4}\;for\;{Q_P}^{-1}\;and\;(0.5{\pm}2.8){\times}10^{-3}\;to\;(1.8{\pm}1.6){\times}10^{-4}\;for\;{Q_S}^{-1}$ in southwestern South Korea. According that a frequency-dependent power law is applied to the data, the best fits of ${Q_P}^{-1}\;and\;{Q_S}^{-1}\;are\;0.003f^{-0.49}\;and\;0.005f^{-1.03}$ in central South Korea, and $0.026f^{-1.47}$ and $0.001f^{-0.49}$ in southwestern South Korea, respectively. These values almost correspond to those of seismically stable regions although ${Q_P}^{-1}$ values of southwestern South Korea are a little high due to lack of data used.