• 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.

• Journal of the Korean earth science society
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• v.36 no.7
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• pp.643-648
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• 2015

Equations that could estimate the local magnitude of historical earthquakes, being difficult to calculate, in Sino-Korea craton was obtained using instrumental earthquake data for 22 Korean and 46 northeastern Chinese events. The obtained equations from intensity $I_0$ is $M_L=1.7+0.57{\times}I_0$. The equation from felt area FA for the Korean Peninsula is $M_L=4.29-1.34{\times}log(FA)+0.28{\times}log^2(FA)$. When the information on earthquake damage, effects, and felt area is all recorded at the same time, the former equation of intensity is more feasible than that of felt area due to uncertainty in earthquake felt area.

• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.97-104
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• 2016

Small to large earthquakes have been reported in Gyeongju and its vicinity in southeast Korea during historical period as well as instrumental observation period. We identified and located more than 300 earthquakes that occurred between January 2010 and December 2014 in a $20km{\times}30km$ area, but were unreported because of their small magnitudes. We used the Joint Hypocenter Determination (JHD) method to minimize the influence of the differences between the actual earth structure and 1-D velocity model for earthquake locations. The potential relationship between the previously reported Quaternary faults and the earthquake hypocenters was investigated. Many micro-earthquakes were found to be located in the southern segment of the Yeonil Tectonic Line, the Seokup fault, and the Waup basin boundary faults.

• Journal of the Korean earth science society
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• v.41 no.3
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• pp.238-247
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• 2020

This study simulated strong ground motion waveforms in the southern Korean Peninsula, based on the physical earthquake modeling of the Southern California Earthquake Center (SCEC) BroadBand Platform (BBP). Characteristics of intensity attenuation were investigated for M 6.0-7.0 events, incorporating the site effects. The SCEC BBP is software generates broadband (0-10 Hz) ground-motion waveforms for earthquake scenarios. Among five available modeling methods in the v16.5 platform, we used the Song Model. Approximately 50 earthquake scenarios each were simulated for M 6.0, 6.5, and 7.0 events. Representative metrics such as peak ground acceleration (PGA) and peak ground velocity (PGV) were obtained from the synthetic waveforms that were simulated before and after the consideration of site effects (V_S30). They were then empirically converted to distribution of instrumental intensity. The intensity that considers the site effects is amplified at low rather than high V_S30 zones.

• Journal of the Korean earth science society
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• v.38 no.7
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• pp.561-569
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• 2017

Fault plane solutions of the Iksan earthquake ($M_L=3.85$) and two aftershocks were obtained using the FOCMEC (FOCal MEChanism determination) program. The main event showed the characteristic of strike slip faulting with reverse component. It has the fault planes with NE-SW or NW-SE direction. This is similar to the fault characteristics of earthquake pattern in the inland area of the Korean Peninsula. In order to detect micro-earthquake events, continuous seismic waveform data of the thirteen seismic stations within a radius of 100km from epicenter were analyzed by PQLII program (PASSCAL, 2017) for the period from December 15, 2015 to January 22, 2016. The epicenters of nineteen micro-events were newly determined by Hypoinverse-2000 program. They are not concentrated along some lineaments or fault lines. The intensity of the Iksan earthquake was obtained by estimating the telephone inquiries, the degree of ground shaking or damage all around the southern peninsula. The instrumental intensity was also obtained using PGA (Peak Ground Acceleration) records. As a result, the maximum MM intensity was estimated to be V near the epicenter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.187-196
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• 2008

An earthquake of magnitude 5.0 occurred at Ssang-gye-sa, a Buddhist temple in Jirisan, located near the southern border of the Korean peninsula on 4 July 1936. It resulted in severe damage of several buildings and structures in Ssang-gye-sa. Particularly, the top component of a five-story stone pagoda in the temple was tipped over and fell down during the earthquake. This earthquake damage case would be usefully applied to estimating the intensity of ground motion in the Korean peninsula, a moderate seismicity region, where strong motion has never been recorded with the exception of historic seismic events. In order to estimate the local site effects and the corresponding ground motion at Ssang-gye-sa site, intensive site investigations including borehole drilling and in-situ seismic tests such as crosshole and SASW tests were performed in the temple area. Based on the site characteristics, site-specific seismic response analyses using various input motions were conducted for a representative Ssang-gye-sa site by means of both one-dimensional equivalent-linear and nonlinear methods with six input rock outcrop acceleration levels ranging from 0.044g to 0.220g. The resultant site-specific seismic responses indicated the amplified ground motions in the short-period range near the site period of Ssang-gye-sa. Furthermore, the intensity on rock outcrop of the 1936 Jirisan earthquake was estimated by making a comparison between the site responses analysis results in this study and the full-scaled seismic test of pagoda model in the prior study.

• Geosciences Journal
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• v.22 no.6
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• pp.871-880
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• 2018

During and shortly after the 2017 Pohang Earthquake ($M_w$ 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground's susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes ($M_w$ > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea.

• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.369-384
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• 2006

Korean Peninsula, located on the southeastern part of Eurasian plate, belongs to the intraplate region. The characteristics of intraplate earthquake show the low and rare seismicity and the sparse and irregular distribution of epicenters comparing to interplate earthquake. To evaluate the exact seismic activity in intraplate region, long-term seismic data including historical earthquake data should be archived. Fortunately the long-term historical earthquake records about 2,000 years are available in Korea Peninsula. By the analysis of this historical and instrumental earthquake data, seismic activity was very high in 16-18 centuries and is more active at the Yellow sea area than East sea area. Comparing to the high seismic activity of the north-eastern China in 16-18 centuries, it is inferred that seismic activity in two regions shows close relationship. Also general trend of epicenter distribution shows the SE-NW direction. In Korea Peninsula, the first seismic station was installed at Incheon in 1905 and 5 additional seismic stations were installed till 1943. There was no seismic station from 1945 to 1962, but a World Wide Standardized Seismograph was installed at Seoul in 1963. In 1990, Korean Meteorological Adminstration(KMA) had established centralized modem seismic network in real-time, consisted of 12 stations. After that time, many institutes tried to expand their own seismic networks in Korea Peninsula. Now KMA operates 35 velocity-type seismic stations and 75 accelerometers and Korea Institute of Geoscience and Mineral Resources operates 32 and 16 stations, respectively. Korea Institute of Nuclear Safety and Korea Electric Power Research Institute operate 4 and 13 stations, consisted of velocity-type and accelerometer. In and around the Korean Peninsula, 27 intraplate earthquake mechanisms since 1936 were analyzed to understand the regional stress orientation and tectonics. These earthquakes are largest ones in this century and may represent the characteristics of earthquake in this region. Focal mechanism of these earthquakes show predominant strike-slip faulting with small amount of thrust components. The average P-axis is almost horizontal ENE-WSW. In north-eastern China, strike-slip faulting is dominant and nearly horizontal average P-axis in ENE-WSW is very similar with the Korean Peninsula. On the other hand, in the eastern part of East Sea, thrust faulting is dominant and average P-axis is horizontal with ESE-WNW. This indicate that not only the subducting Pacific Plate in east but also the indenting Indian Plate controls earthquake mechanism in the far east of the Eurasian Plate. Crustal velocity model is very important to determine the hypocenters of the local earthquakes. But the crust model in and around Korean Peninsula is not clear till now, because the sufficient seismic data could not accumulated. To solve this problem, reflection and refraction seismic survey and seismic wave analysis method were simultaneously applied to two long cross-section traversing the southern Korean Peninsula since 2002. This survey should be continuously conducted.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.97-102
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• 1988

The strain release associated with historical and instrumental earthquoke data are analyzed. In addition, the relationship between engineering intensity and cumulative frequency of earthquake occurrence is investigated. Based on the study, a seimic zoning map of the Korean peninsula is constructed. For each seismic zone, a peak ground acceleration value is determined for the aseismic designs of two types of structures. First type is general structures like buildings and the second type is special structures like nuclear power plants.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.1
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• pp.69-77
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• 1997

An intensity survey on the 13 December 1996 Yeogweol earthquake has mode for 262 locations throughout southern part of Korean peninsula, then we investigated attenuation properties in the south Korean region as well as intensities distribution. In this study, intensities are estimated to be from II to possibly VIII. The iso-seismal intensity map we obtained shows general pattern of intensity distribution in the south korean region quite clearly despite the inherent uncertainties included in the process of intensity estimation. In case of intensity larger than VI, considerable damages such as fracturing walls are frequently reported. One of the significant feature of this intensity map is, considering its magnitude 4.5 reported by KMA, the felt area is unusually large covering most of the Korean Peninsular except Cheju island. This result indicates either the magnitude is under estimated or the focal depth is much deeper than expected. Assuming indicates either the magnitude is under estimated or the focal depth is much deeper than expected. Assuming shallow earthquake whose focal depth is by iso-seismal contour lines for intensity IV to VII, respectively. To resolve this ambiguity, more reliable estimation of focal depth and magnitude by using telesesmic instrumental records should be made in the future.