• Journal of the Korean Association of Geographic Information Studies
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• v.11 no.2
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• pp.38-50
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• 2008

The site-specific seismic responses and corresponding seismic hazards are influenced mainly by the subsurface geologic and geotechnical dynamic characteristics. To estimate reliably the seismic responses in this study, a geotechnical information system (GTIS) within GIS framework was developed by introducing new concepts, which consist of the extended area containing the study area and the additional site visit for acquiring surface geo-knowledge data. The GIS-based GTIS was built for Gyeongju area, which has records of abundant historical seismic hazards reflecting the high potential of future earthquakes. At the study area, Gyeongju, intensive site investigations and pre-existing geotechnical data collections were performed and the site visits were additionally carried out for assessing geotechnical characteristics and shear wave velocity ($V_S$) representing dynamic property. Within the GTIS for Gyeongju area, the spatially distributed geotechnical layers and $V_S$ in the entire study area were reliably predicted from the site investigation data using the geostatistical kriging method. Based on the spatial geotechnical layers and $V_S$ predicted within the GTIS, a seismic zoning map on site period ($T_G$) from which the site-specific seismic responses according to the site effects can be estimated was created across the study area of Gyeongju. The spatial $T_G$ map at Gyeongju indicated seismic vulnerability of two- to five-storied buildings. In this study, the seismic zonation based on $T_G$ within the GIS-based GTIS was presented as regional efficient strategy for seismic hazard prediction and mitigation.

• The Journal of Engineering Geology
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• v.29 no.1
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• pp.1-12
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• 2019

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.

• Korean Journal of Remote Sensing
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• v.36 no.6_1
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• pp.1367-1377
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• 2020

The purpose of this study is to assess the seismic vulnerability of buildings in Gyeongju city starting with the earthquake that occurred in the city on September 12, 2016, and produce a seismic vulnerability map. 11 influence factors related to geotechnical, physical, and structural indicators were selected to assess the seismic vulnerability, and these were applied as independent variables. For a dependent variable, location data of the buildings that were actually damaged in the 9.12 Gyeongju Earthquake was used. The assessment model was constructed based on random forest (RF) as a mechanic study method and support vector machine (SVM), and the training and test dataset were randomly selected with a ratio of 70:30. For accuracy verification, the receiver operating characteristic (ROC) curve was used to select an optimum model, and the accuracy of each model appeared to be 1.000 for RF and 0.998 for SVM, respectively. In addition, the prediction accuracy was shown as 0.947 and 0.926 for RF and SVM, respectively. The prediction values of the entire buildings in Gyeongju were derived on the basis of the RF model, and these were graded and used to produce the seismic vulnerability map. As a result of reviewing the distribution of building classes as an administrative unit, Hwangnam, Wolseong, Seondo, and Naenam turned out to be highly vulnerable regions, and Yangbuk, Gangdong, Yangnam, and Gampo turned out to be relatively safer regions.

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.13-23
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• 1998

An intensity of the 1997 Kyungju earthquake(M=4.3) was estimated at three hundred locations based on the field survey and questionaires from 2200 residents. The isoseismal shows almost circular pattern which doesnot reflect some specific geological trends. However,most of the Kyeongsang basin except the southwestern part is included within the area of MM intensity V. There occurred strong shaking, numerous cracks on the wall of the houses, and movement of slate on the roofs, falling of the tiles from the monument. The isoseismal of the highest MM intensity VII, 1-3 km in width and 9 km in length, is elongated along the Yangsan fault, which is located about 1.5 km west from epicenter. The lineaments near the epicenter exhibit almost N-S and NNE directions. The lineament distribution, the pattern of damage area and the solution of fault plane suggest that the Kyongju earthquake occurred with strike-slip sense along the Yangsan fault. The calculated intensity attenuation(I) with distance(R) is as follows : $I{\;}={\;}I_o{\;}+{\;}0.3461{\;}-{\;}0.3274{\;}{\times}{\;}1nR{\;}-{\;}0.086{\;}{\times}{\;}R$.

• 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.

• Korean Journal of Remote Sensing
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• v.37 no.3
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• pp.649-655
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• 2021

This study purposes to cross-validate its performance by applying the optimal seismic vulnerability assessment model based on previous studies conducted in Gyeongju to other regions. The test area was Pohang City, the occurrence site for the 2017 Pohang Earthquake, and the dataset was built the same influencing factors and earthquake-damaged buildings as in the previous studies. The validation dataset was built via random sampling, and the prediction accuracy was derived by applying it to a model based on a random forest (RF) of Gyeongju. The accuracy of the model success and prediction in Gyeongju was 100% and 94.9%, respectively, and as a result of confirming the prediction accuracy by applying the Pohang validation dataset, it appeared as 70.4%.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.3
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• pp.99-105
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• 2000

한반도 동남부 지역에서 발생하고 관찰된 약진 또는 중진의 자료를 이영하여 이 지역의 Q값과 지진원의 특성인 모서리 주파수 (fc), 응력강하량(Δ$\delta$) 및 모멘크규모 (Mw)를 산정하였다. 가속도 스펙트럼의 경사와 관련된 x의 통계학적 분포로부터 추정한 Q의 95% 신뢰범위는 1656~2454 이다. 1998년 1월 18일 울산 앞바다 지진과 1997년 6월 26일 경주지진의 지진원 요소를 구한 결과 fc 는 각각 4.22Hz , 2.94Hz, Δ$\delta$는 각각 106.8 bar, 106.2 bar, Mw는 각각 3.9, 4.0으로 추정되었다. 제한된 자료수로 인하여 이들의 통계학적 성질을 충분히 규명하지는 못하였지만 다른 연구자들의 기존결과와 유사한 값을 보인다. 본 연구의 결과는 강진동 모사에 직접 이용이 가능하며, 이 지역에 위치한 원자력 발전소 내진 안전성 검토에도 이용될 수 있다.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2016.11a
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• pp.357-358
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• 2016

최근 재난에 대한 광역적 탐지 및 피해상황을 예측하는데 위성레이더 영상의 활용방안이 대두되고 있다. 본 논문에서는 SENTINEL-1 위성레이더 영상을 활용하여 지진발생으로 인한 지표변위를 관측하고자 하였다. 차분간섭기법(DinSAR)을 적용하여 최근 발생한 이탈리아 중부 지진과 한반도 경주 지진의 지표변위를 관측하고 피해범위를 예측하였다. 연구결과 규모 6.4 이탈리아 지진에서 최대 20.1cm의 침하를 관측하였으며, 규모 5.8 경주 지진의 경우 발생지역 20km 범위에서 약 3cm의 지표변위를 관측하였다. 향후 지상 SAR 자료를 구축할 예정이며 재난지역의 다각적 관측자료 취득 및 보다 정확한 재난 피해를 파악 할 수 있을 것으로 기대한다.

• Economic and Environmental Geology
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• v.51 no.4
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• pp.393-400
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• 2018

Despite some skeptical views on the possibility of earthquake prediction, observation and evaluation of precursory changes have been continued throughout the world. In Korea, the public concern on the earthquake prediction has been increased after 2016 $M_L5.8$ and 2017 $M_L5.4$ earthquakes occurred in Gyeongju and Pohang, the southeastern part in Korea, respectively. In this study, the abnormal increase of groundwater level was observed before the 2016 $M_L5.8$ Gyeongju earthquake in a borehole located in 52 km away from the epicenter. The well was installed in the Yangsan fault zone, and equipped for the earthquake surveillance. The abnormal change in the well would seem to be a precursor, considering the hydrogeological condition and the observations from previous studies. It is necessary to set up a specialized council to support and evaluate the earthquake prediction and related researches for the preparation of future earthquake hazards.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2017.11a
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• pp.262-263
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• 2017

경주 지진 발생 지점의 반경 30km에는 사고대비물질 취급 업체가 353개였고, 이 중 90% 이상이 오래된 내진설계가 반영되어 노후화가 심한 것으로 나타났다. 이에 사고대비물질, 고압장비 등의 취급 비중이 높은 산업단지 및 입주 기업체의 매뉴얼 개발의 핵심인 사내 방재 조직 편성에 필요한 항목들을 연구 도출하였다. 방재 조직의 큰 틀은 재해대책본부장(대표), 비상대책위원회(부서장), 현장지휘반으로 구성하였으며, 지진 대응 실무를 담당하는 현장지휘반의 역할을 정리하였다. 사내 방재 조직의 각 부서는 대비, 대응, 복구 단계의 역할을 숙지 및 훈련하여 1차 지진 대응 단체로서 피해를 최소화 시켜야 한다.