• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.3
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• pp.185-191
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• 2018

Post-earthquake risk assessment technique in Korea is developed in 2013 by National Disaster Management Research Institute, at the same time, related manual and standard regulation is distributed to every local government by National Emergency Management Agency. The objectives of this research are to investigate and evaluate the post-earthquake risk assessment of 9.12 Earthquake (M5.8, Gyeongju City, 2016) and 11.15 Earthquake (M5.4, Pohang City, 2017). To suggest and improve the assessment process of post-earthquake risk, first post-earthquake risk assessment method of advanced foreign countries including US, New Zealand and Japan are compared, and post-earthquake evaluation activities in 9.12 Earthquake and 11.15 Earthquake are analyzed. From the results, it is needed to expand the adapted building and structure types and strengthen the earthquake disaster response capacity of local government.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.561-567
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• 2016

After the Gyeong-ju 9.12 earthquake, we found the necessity of seismic design of nonstructural element is important to reduce damages in view of properties and economic losses. This study focused on the investigation of damages including both properties and human beings. It was found that most of the damages are leaking of water pipe line, rupture of glasses, spalling of roof finishing, cracks of building, and falling from roof. It was also found that the seismic design force of nonstructural elements is taking account into the natural periods, amplification factors, response modification factors to forsee inelastic behaviors. From this studies, it is recommended that more studies are necessary on the seismic design force of nonstructural element.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.3
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• pp.175-184
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• 2018

In this paper, comparative analysis of the 9.12 Gyeongju and 11.15 Pohang earthquakes was conducted in order to provide probable explanations and reasons for the damage observed in the 11.15 Pohang earthquake from both earthquake and structural engineering perspectives. The damage potentials like Arias intensity, effective peak ground acceleration, etc observed in the 11.15 Pohang earthquake were generally weaker than those of the 9.12 Gyeongju earthquake. However, in contrast to the high-frequency dominant nature of the 9.12 Gyeongju earthquake records, the spectral power of PHA2 record observed in the soft soil site was highly concentrated around 2Hz. The base shear around 2 Hz frequency was as high as 40% building weight. This frequency band is very close to the fundamental frequency of the piloti-type buildings severely damaged in the northern part of Pohang. Unfortunately, in addition to inherent vertical irregularity, most of the damaged piloti-type buildings had plan irregularity as well and were non-seismic. All these contributed to the fatal damage. Inelastic dynamic analysis indicated that PHA2 record demands system ductility capacity of 3.5 for a structure with a fundamental period of 0.5 sec and yield base shear strength of 10% building weight. The system ductility level of 3.5 seems very difficult to be achievable in non-seismic brittle piloti-type buildings. The soil profile of the PHA2 site was inversely estimated based on deconvolution technique and trial-error procedure with utilizing available records measured at several rock sites during the 11.15 Pohang earthquake. The soil profile estimated was very typical of soil class D, implying significant soil amplification in the 11.15 Pohang earthquake. The 11.15 Pohang earthquake gave us the expensive lesson that near-collapse damage to irregular and brittle buildings is highly possible when soil is soft and epicenter is close, although the earthquake magnitude is just minor to moderate (M 5+).

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.3
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• pp.467-475
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• 2018

Recently earthquakes have been increasing worldwide, and the largest earthquake of 5.8 on the Richter scale occurred on September 12, 2016 in the Gyeongju area. After the earthquake, more than 200 aftershocks have occurred from January 2017 to December 2017. The largest earthquake in 2017 was a 4.3-magnitude earthquake near Pohang on November 15. In this study, we tried to analyze the coordinate change due to the earthquake using the data of the CORS(Continuously Operating Reference Station) in Korea. In order to analyze the change of coordinates due to the earthquake in Pohang area on November 15, 2017, data processing was performed by kinematic method. And from January 2017 to December 2017, observation data of 9 stations in Korea were analyzed by relative positioning method and the change of coordinates due to earthquake was analyzed. As a result of the study, it was possible to estimate the instantaneous coordinate change due to the earthquake through the kinematic positioning, and it was suggested that there is no change in the coordinates of the domestic CORS by the relative positioning results. After the 2017 Gyeongju earthquake, aftershocks continue to occur, and it is necessary to monitor the area continuously.

• Computational Structural Engineering
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• v.5 no.1
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• pp.91-96
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• 1992

Earthquake resistant design is evolutionary, and, although great progress has been made since seismic design was made mandatory by building codes, it is still not completely understood. In this paper, a 10 story steel building is analyzed and its results are compared by applying two different actual ground motions to the structure. 12 sets of Loma Prieta, California, earthquake data which occurred in 1989, and recorded 7.1 on the Richter scale and 9 sets of Valparaiso, Chile, earthquake data which occurred in 1985, and recorded 7.8 on the Richter scale were scaled to zone 2B level of UBC-88. By applying earthquake ground motions which had similar Richter scale magnitude, it was found that the Chile earthquake which had long duration of ground motion affected about twice bigger than that of California earthquake which had relatively short duration of ground motion. In addition to the peak ground motion, the duration of the ground motion is a very important factor in structural design.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.527-536
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• 2016

This paper investigates seismic damage potential of recent September 12 M5.8 Gyeongju earthquake from diverse earthquake engineering perspectives using the accelerograms recorded at three stations near the epicenter. In time domain, strong motion durations are evaluated based on the accelerograms and compared with statistical averages of the ground motions with similar magnitude, epicentral distance and soil conditions, while Fourier analysis using FFT is performed to identify damaging frequency contents contained in the earthquake. Effective peak ground accelerations are evaluated from the calculated response spectra and compared with apparent peak ground accelerations and the design spectrum in KBC 2016. All these results are used to consistently explain the reason why most of seismic damage in the earthquake was concentrated on low-rise stiff buildings but not quite significant. In order to comparatively appraise the damage potential, the constant ductility spectrum constructed from the Gyeongju earthquake is compared with that of the well-known 1940 El Centro earthquake. Deconvolution analysis by using one accelerogram speculated to be recorded at a stiff soil site is also performed to estimate the soil profile conforming to the response spectrum characteristics. Finally, response history analysis for 39- and 61-story tall buildings is performed as a case study to explain significant building vibration felt on the upper floors of some tall buildings in Busan area during the Gyeongju earthquake. Seismic design and retrofit implications of M5.8 Gyeongju earthquake are summarized for further research efforts and improvements of relevant practice.

• 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.

• 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%.

• Earthquakes and Structures
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• v.9 no.1
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• pp.93-109
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• 2015

Based on the reconnaissance of buildings in Dujiangyan City during 2008 Wenchuan earthquake, China, structural damage characteristics and the spatial distribution of structural damage are investigated, and the possible reasons for the extraordinary features are discussed with consideration of the influence of urban historical evolution and spatial variation of earthquake motions. Firstly, the urban plan and typical characteristics of structural seismic damage are briefly presented and summarized. Spatial distribution of structural damage is then comparatively analyzed by classifying all surveyed buildings in accordance with different construction age, considering the influence of seismic design code on urban buildings. Finally, the influences of evolution of seismic design code, topographic condition, local site and distance from fault rupture on spatial distribution of structural damage are comprehensively discussed. It is concluded that spatial variation of earthquake motions, resulting from topography, local site effect and fault rupture, are very important factor leading to the extraordinary spatial distribution of building damage except the evolution of seismic design codes. It is necessary that the spatial distribution of earthquake motions should be considered in seismic design of structures located in complicated topography area and near active faults.

• Journal of Environmental Science International
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• v.12 no.6
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• pp.677-688
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• 2003

The purpose of this study was to predict occurrence of earthquakes in Korea by measuring the concentration of radon radioactivity in the air and in the underground water. Two monitoring systems of radon concentration detection in the air were installed in Seoul, East Coast area, whereas of radon concentration in the underground water in Kyungju area during December, 1999 to June, 2001. The distribution of radon concentration in the air in Seoul is as follows Winter(10.10 $\pm$ 2.81 Bq/㎥), autumn(8.41 $\pm$ 1.35 Bq/㎥), summer(5.83 $\pm$ 0.05 Bq/㎥) and spring (5.34 $\pm$ 0.44 Bq/㎥), whereas the distribution of radon in the air in the East Coast area showed some difference as follows : autumn (14.08 $\pm$ 5.75 Bq/㎥), Summer (12.04 $\pm$ 0.53 Bq/㎥), Winter (12.02 $\pm$ 1.40 Bq/㎥) and spring (8.93 $\pm$ 0.91 Bq/㎥). In the meanwhile, the distribution of radon in the water is as follows : spring (123.59 $\pm$ 16.36count/10min), Winter (93.95 $\pm$ 79.69counter/10min), autumn (68.96 $\pm$ 37.53counter/10min) and spring (34.45 $\pm$ 9.69counter/10min). The daily range of the density of radon concentration in Seoul and East Coast area was between 5.51 Bq/㎥ - 9.44 Bq/㎥, 7.15 Bq/㎥ - 15.27 Bq/㎥, respectively. Correlation of the distributions of radon concentrations in the air and in underground water with earthquake showed considerable variations of radon concentration before the occurrence of the earthquake. The results suggested that radon radioactivity seemed to be helpful for the prediction of the occurrence of earthquake.