• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.512-518
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• 2018

This article measured and analyzed the indoor radon concentrations at one university building in Gyeongju, Republic of Korea, to investigate if there is any relationship between earthquakes and indoor radon concentration. Since 12 September 2016, when two 5.1 and 5.8 magnitude earthquakes occurred, hundreds of aftershocks affected Gyeongju until January 2017. The measurements were made at the ground floor of the Energy Engineering Hall of Dongguk University in Gyeongju over a period between February 2016 and January 2017. The measurements were made with an RAD7 detector on the basis of the US Environmental Protection Agency measurement protocol. Each measurement was continuously made every 30 minutes over the measurement period every month. Among earthquakes with 2.0 or greater magnitude, the earthquakes whose occurrence timings fell into the measurement periods were screened for further analysis. We observed similar spike-like patterns between the indoor radon concentration distributions and earthquakes: a sudden increase in the peak indoor radon concentration 1-4 days before an earthquake, gradual decrease before the earthquake, and sudden drop on the day of the earthquake if the interval between successive earthquakes was moderately longer, for example, 3 days in this article.

• Journal of Soil and Groundwater Environment
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• v.21 no.6
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• pp.80-86
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• 2016

Earthquakes of M5.1, M5.8 and M4.5 occurred in September 12 and 19 respectively in Gyeongju, Gyeongbuk Province. Theses earthquakes inflated fears of people and highlighted necessity of detailed countermeasures because we have considered our country is safe to earthquakes. In the meanwhile, earthquake also impacts groundwater and thus it was recently reported that the Gyeongju Earthquakes affected groundwater there. This study evaluates daily groundwater data collected from five national groundwater monitoring stations (Geoncheon, Sannae, Oedong, Yangbuksin, Cheonbuk) in Gyeongju. The analysis revealed that only groundwater level of bedrock monitoring well hosted in andesite exhibited earthquake impact while no wells in the other four stations hosted in sedimentary rocks showed substantial responses to the earthquakes. This may be derived from the difference of seismic velocity of hosting rocks as well as epicenter distance. Special interest on groundwater monitoring is required to predict earthquakes as precursory phenomena.

• Korean Journal of Remote Sensing
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• v.37 no.1
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• pp.13-22
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• 2021

The ML 5.8 earthquake shocked Gyeongju, Korea, at 11:32:55 UTC on September 12, 2016. One year later, on the afternoon of November 15, 2017, the ML 5.4 earthquake occurred in Pohang, South Korea. The earthquakes injured many residents, damaged buildings, and affected the economy of Gyeongju and Pohang. The damage proxy maps (DPMs) were generated from Sentinel-1 synthetic aperture radar (SAR) imagery by comparing pre- and co-events interferometric coherences to identify anomalous changes that indicate damaged by the earthquakes. DPMs manage to detect coherence loss in residential and commercial areas in both Gyeongju and Pohang earthquakes. We found that our results show a good correlation with the Korea Meteorological Administration (KMA) report with Modified Mercalli Intensity (MMI) scale values of more than VII (seven). The color scale of Sentinel-1 DPMs indicates an increasingly significant change in the area covered by the pixel, delineating collapsed walls and roofs from the official report. The resulting maps can be used to assess the distribution of seismic damage after the Gyeongju and Pohang earthquakes and can also be used as inventory data of damaged buildings to map seismic vulnerability using machine learning in Gyeongju or Pohang.

• Geophysics and Geophysical Exploration
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• v.20 no.3
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• pp.185-192
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• 2017

A sequence of earthquakes with the main shock $M_L$ 5.8 occurred on September 12 2016 in the Gyeongju area. The main shock was the largest earthquakes in the southern part of the Korean peninsula since the instrumental seismic observation began in the peninsula in 1905 and clearly demonstrated that the Yangsan fault is seismically active. The mean focal depth of the foreshock, main shock, and aftershock of the Gyeongju earthquakes estimated by the crustal model of single layer of the Korean peninsula without the Conrad discontinuity turns out to be 12.9 km, which is 2.8 km lower than that estimated based on the IASP91 reference model with the Conrad discontinuity. The distribution of the historical and instrumental earthquakes in the Gyeongju area indicates that the Yangsan fault system comprising the main Yangsan fault and its subsidiary faults is a large fracture zone. The epicenters of the Gyeongju earthquakes show that a few faults of the Yangsan fault system are involved in the release of the strain energy accumulated in the area. That the major earthquakes of Gyeongju earthquakes occurred not on the surface but below 10 km depth suggests the necessity of the study of the distribution of deep active faults of the Yangsan fault system. The magnitude of maximum earthquake of the Gyeongju area estimated based on the earthquake data of the area turns out to be 7.3. The recurrence intervals of the earthquakes over magnitudes 5.0, 6.0 and 7.0 based on the earthquake data since 1978, which is the most complete data in the peninsula, are estimated as 80, 670, and 5,900 years, respectively. The September 2016 Gyeongju earthquakes are basically intraplate earthquakes not related to the Great East Japan earthquake of March 11 2011 which is interplate earthquake.

• Earthquakes and Structures
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• v.20 no.3
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• pp.337-351
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• 2021

On September 12, 2016, the Gyeongju earthquake occurred in the south-eastern region of the Korean peninsula. The event was ranked as the largest magnitude earthquake (=5.8) since instrumental recording was started by the Korean Metrological Administration (KMA) in 1978. The objective of this study is to provide information obtained from the 2016 Gyeongju earthquake and to propose a procedure estimating seismic risk of a typical old RC building for past and potential earthquakes. Ground motions are simulated using the point source model at 4941 grid locations in the Korean peninsula that resulted from the Gyeongju earthquake and from potential future earthquakes with the same hypocenter considering different soil conditions. Nonlinear response history analyses are conducted for each grid location using a three-story gravity-designed reinforced concrete (RC) frame that most closely represents conventional old school and public buildings. Then, contour maps are constructed to present the seismic risk associated with this building for the Gyeongju earthquake and potential future scenario earthquakes. These contour maps can be useful in the development of a mitigation plan for potential earthquake damage to school and public buildings at all grid locations on the Korean peninsula.

• Journal of the Korean earth science society
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• v.39 no.4
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• pp.342-348
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• 2018

An earthquake of $M_L$ 5.8 hit the Gyeongju area on September 12, 2016. A sequence of foreshock-mainshock-aftershock of 588 events with equal to or greater than magnitude 1.5 occurred for six months in this area. Around ninety-nine percentage (98.8%) of the total energy was released intensively within a day, and about 80% of the total events took place within a month after the Gyeongju earthquake. The epicentral distribution of aftershocks of major events ($M_L$ 5.1, 5.8, 4.5, and 3.5) were elongated in the direction of $N30^{\circ}E$. They correlate well with the focal mechanism solution. These facts support the inference that the Gyeongju earthquakes occurred on a sub-parallel subsidiary fault of the Yangsan fault zone or on the linking damage zones between Deokcheon and Yangsan fault. During the last six years before the Gyeongju earthquake, there were few events within 10-km radius from the epicenter. This seismic gap area was filled with a sequence of the Gyeongju earthquakes. The b value for aftershock of the Gyeongju earthquakes is 1.09.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.425-434
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• 2016

This study investigates important parameters used to determine an effective peak ground acceleration (EPGA) based on the characteristics of response spectra of historical earthquakes occurred at Korean peninsula. EPGAs are very important since they are implemented in the Korean Building Code for the seismic design of new structures. Recently, the Gyeongju earthquakes with the largest magnitude in earthquakes measured at Korea took place and resulted in non-structural and structural damage, which their EPGAs should need to be evaluated. This paper first describes the basic concepts on EPGAs and the EPGAs of the Gyeongju earthquakes are then evaluated and compared according to epicentral distances, site classes and directions of seismic waves. The EPGAs are dependant on normalizing factors and ranges of period on response spectrum constructed with the Gyeongju earthquake records. Using the normalizing factors and the ranges of period determined based on the characteristics of domestic response spectra, this paper draw a conclusion that the EPGAs are estimated to be about 30 % of the measured peak ground accelerations (PGA).

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.6
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• pp.295-301
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• 2017

This paper relates to the study of load characteristics applicable to wind turbine generators induced by earthquakes. An artificial design earthquake wave generated through the target spectrum and the envelope function of Richter Magnitude Scale (ML) 7.0 as in ASCE4-98 was created. A simulation of earthquake loads were performed according to the design load cases (DLC) 9.5~9.7 of GL guidelines. Additionally, simulation of seismic loads experienced by Wind Turbines installed in the Gyeongju region were carried out utilizing artificial earthquakes of ML 5.8 simulating the real earthquakes during the Gyeongju Earthquakes of Sept. 2016.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1577-1586
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• 2023

Safety qualification of a steam generator is a crucial issue related to faulted condition design loads, including earthquake loads, and it should be ensured that the structural integrity of a steam generator does not exceed its design load. Using data from the Gyeongju and Pohang earthquakes, the two most powerful recorded seismic events in Korea, seismic analyses of a typical steam generator are conducted in this study. The modal characteristics are used to develop an input deck for these analyses. With a time history analysis, the responses of the steam generator in the event of an earthquake are obtained. In particular, the displacement, velocity, and acceleration responses are obtained in the time domain, with these outcomes then used for a detailed structural analysis as part of the ensuing assessment. The response spectra are also generated to determine the response characteristics in the frequency domain, focusing on the response comparisons between the Gyeongju and Pohang earthquakes. Structural integrity can be ensured by performing additional analysis using results obtained from the time history analysis considering the input excitations of various earthquakes considered in the design.

• Journal of Korean Library and Information Science Society
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• v.48 no.2
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• pp.53-72
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• 2017

The purpose of this study is to analyze types and features social issues about the Gyeongju earthquakes 2016, South Korea. The specific purpose is to identify types of topics related to Gyeongju Earthquakes, changes of topics over time, and the differences of topics depending on the each type of newspapers. According to the result of topic modeling, 55 topics were extracted. The result of this study is following these. First, the main topics have been changed with the course of time. In September, various topics were emerged, specifically urgent issues was found during two weeks after the first earthquake. After October, topics about social problems derived from the earthquakes received much attention at that time. Topics related to safety problems about nuclear plant have steadily found in all period. Second, topics varied depending whether the newspaper is national or regional. Also, differences of topics were found when dividing the newspapers by their characteristics considered conservative or liberal.