• The Journal of the Petrological Society of Korea
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• v.25 no.3
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• pp.253-260
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• 2016

A moment magnitude 3.1 earthquake occurred in the Seoul metropolitan region (SMR), Korea, on 9 February 2010. The unexpected shaking attracted much attention and raised concerns about the seismic hazards and risks in the SMR, which was regarded as an area safe from any earthquake hazard. The SMR has a population of 25 million and is one of the largest metropolitan areas in the world. A shakemap for a scenario earthquake with magnitude 6.5 and focal depth 12 km implies that the SMR will be exposed to serious risk because of its large population and the high vulnerability of its buildings. Although the instrumentally recorded earthquakes discussed in this article cannot be classified as major events, they should not be discounted as insignificant. Considering the low seismicity, micro-earthquakes below the magnitude of a conventional seismic network can achieve would be used to estimate background information in the evaluation of earthquake hazards and risks.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.6
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• pp.600-618
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• 2014

The metadata for urban meteorological observation is standardized through comparison with those established at the World Meteorological Organization and the Korea Meteorological Administration to understand the surrounding environment around the sites exactly and maintain the networks and sites efficiently. It categorizes into metadata for an observational network and observational sites. The latter is again divided into the metadata for station general information, local scale information, micro scale information, and visual information in order to explain urban environment in detail. The metadata also contains the static information such as urban structure, surface cover, metabolism, communication, building density, roof type, moisture/heat sources, and traffic as well as the update information on the environment change, maintenance, replacement, and/or calibration of sensors. The standardized metadata for urban meteorological observation is applied to the Weather Information Service Engine (WISE) integrated meteorological sensor network and sites installed at Incheon area. It will be very useful for site manager as well as researchers in fields of urban meteorology, radiation, surface energy balance, anthropogenic heat, turbulence, heat storage, and boundary layer processes.

• Structural Engineering and Mechanics
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• v.56 no.2
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• pp.293-315
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• 2015

While most of researches on system identification of building structures are aimed at finding modal parameters first and identifying the corresponding physical parameters by using the transformation in terms of transfer functions and cross spectra, etc., direct physical parameter system identification methods have been proposed recently. Due to the problem of signal/noise (SN) ratios, the previous methods are restricted mostly to earthquake records or forced vibration data. In this paper, a theoretical investigation is performed on the influence of wind disturbances on stiffness identification of building structures using micro-tremor at limited floors. It is concluded that the influence of wind disturbances on stiffness identification of building structures using micro-tremor at limited floors is restricted in case of using time-series data for low-rise buildings and does not cause serious problems.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.592-599
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• 2020

This paper proposes a Convolutional Recurrent Neural Net (CRNN) structure that can simultaneously reflect both static and dynamic characteristics of seismic waveforms for various earthquake events classification. Addressing various earthquake events, including not only micro-earthquakes and artificial-earthquakes but also macro-earthquakes, requires both effective feature extraction and a classifier that can discriminate seismic waveform under noisy environment. First, we extract the static characteristics of seismic waveform through an attention-based convolution layer. Then, the extracted feature-map is sequentially injected as input to a multi-input single-output Long Short-Term Memory (LSTM) network structure to extract the dynamic characteristic for various seismic event classifications. Subsequently, we perform earthquake events classification through two fully connected layers and softmax function. Representative experimental results using domestic and foreign earthquake database show that the proposed model provides an effective structure for various earthquake events classification.

• Asian Journal for Public Opinion Research
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• v.1 no.4
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• pp.249-267
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• 2014

Social media is being increasingly utilized in disaster relief work to identify safety issues, locate displaced-victims, and seek or provide support for those who need help. The presence of social media in disaster management has changed significantly in recent years, as it was not prevalent in the 2008 Wenchuan earthquake, but had become a powerful force in the 2013 Ya'an earthquake. This paper discusses the development of social media in disaster management via making a comparison between how it functioned in the two earthquakes. It examines the following aspects: who are the stakeholders that use social media in the earthquake management; how do they adopt this means in response to the earthquakes; and what are the outcomes of adopting social media with regards to public engagement and collaboration in an emergency event. As Sina Weibo acts as the equivalent of China's Twitter, the methodology relies on an analysis of posts in Weibo. The outcomes primarily show that: (1) authorities, celebrities and the public actively adopted social media for the purpose of information dissemination and resource mobilization; and (2) social media users are both content consumers and content generators in the times of earthquakes. The study concludes that social media as a backchannel communication tool is helpful for government institutions, corporations, and nonprofit organizations to build relationships with their stakeholders in the disaster management cycle. The result will interest academics and emergency management practitioners who are concerned with improving disaster communication.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.1-7
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• 2005

The optimal seismic retrofitting of NPP(Nuclear Power Plant) cabinet structures that contain seismic category 1 relays was studied in this paper. During earthquake event, the failure modes of relays are not appeared in form of structural failure, but are appeared in form of contact chatter of relay. Therefore, the retrofitting of cabinet has to be aimed at the reducing of the structural response, such as acceleration. In this study, the optimal characteristic values of dampers were searched by ${\mu}$-GA (micro-Genetic Algorithm) scheme for several installation patterns. To keep accuracy and efficiency of analysis, the structural models of cabinet were considered as a frame structure. The responses of structure were obtained inform of acceleration response spectra derived from the results of nonlinear time history analysis including damping nonlinearity. The objective function of the optimum procedure was constructed based on the maximum ratio of maximum spectral value and target GERS (General Equipment Ruggedness Spectra). The results show the good improvements of fitness for adequate retrofitting pattern. Especially, the improvements of fitness were remarkable when the values of damping exponents are low.

• Earthquakes and Structures
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• v.12 no.6
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• pp.689-697
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• 2017

Nowadays, there are a great number of various structures that have been retrofitted by using different FRP Composites. Due to this, more researches need to be conducted to know more the characteristics of these structures, not only that but also a comparison among them before and after the retrofitting is needed. In this research, a model steel structure is tested using a bench-scale earthquake simulator on the shake table, using recorded micro tremor data, in order to get the dynamic behaviors. Beams of the model steel structure are then retrofitted by using CFRP composite, and then tested on the Quanser shake table by using the recorded micro tremor data. At this stage, it is needed to evaluate the dynamic behaviors of the retrofitted model steel structure. Various types of methods of OMA, such as EFDD, SSI, etc. are used to take action in the ambient responses. Having a purpose to learn more about the effects of FRP composite, experimental model analysis of both types (retrofitted and no-retrofitted models) is conducted to evaluate their dynamic behaviors. There is a provision of ambient excitation to the shake table by using recorded micro tremor ambient vibration data on ground level. Furthermore, the Enhanced Frequency Domain decomposition is used through output-only modal identification. At the end of this study, moderate correlation is obtained between mode shapes, periods and damping ratios. The aim of this research is to show and determine the effects of CFRP Composite implementation on structural responses of the model steel structure, in terms of changing its dynamical behaviors. The frequencies for model steel structure and the retrofitted model steel structure are shown to be 34.43% in average difference. Finally, it is shown that, in order to evaluate the period and rigidity of retrofitted structures, OMA might be used.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.251-256
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• 2017

The electric coupling between the lithosphere and the ionosphere is examined. The electric field is considered as a timevarying irregular vertical Coulomb field presumably produced on the Earth's surface before an earthquake within its epicentral zone by some micro-processes in the lithosphere. It is shown that the Fourier component of this electric field with a frequency of 500 Hz and a horizontal scale-size of 100 km produces in the nighttime ionosphere of high and middle latitudes a transverse electric field with a magnitude of ~20 mV/m if the peak value of the amplitude of this Fourier component is just 30 V/m. The time-varying vertical Coulomb field with a frequency of 500 Hz penetrates from the ground into the ionosphere by a factor of ${\sim}7{\times}10^5$ more efficient than a time independent vertical electrostatic field of the same scale size. The transverse electric field with amplitude of 20 mV/m will cause perturbations in the nighttime F region electron density through heating the F region plasma resulting in a reduction of the downward plasma flux from the protonosphere and an excitation of acoustic gravity waves.

• Earthquakes and Structures
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• v.16 no.6
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• pp.727-741
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• 2019

A reinforced concrete water tank is a typical functional liquid storage structure and cracks are the greatest threat to the liquid storage structure. Tanks are readily cracked due to seismic activity, thereby leading to the leakage of the stored liquid and a loss of function. In order to study the effect of cracks on liquid storage tanks, self-healing and leakage tests for bending cracks and through cracks in the walls of a reinforced concrete water tank were conducted. Material performance tests were also performed. The self-healing performance of bending cracks in a lentic environment and through cracks in a lotic environment were tested, thereby the self-healing width of bending micro-cracks in the lentic environment in the short term were determined. The through cracks had the capacity for self-healing in the lotic environment was found. The leakage characteristics of the bending cracks and through cracks were tested with the actual water head on the crack. The effects on liquid leakage of the width of bending cracks, the depth of the compression zone, and the acting head were determined. The relationships between the leakage rate and time with the height of the water head were analyzed. Based on the tests, the relationships between the crack characteristics and self-healing as well as the leakage were obtained. Thereby the references for water tank structure design and grading earthquake damage were provided.

• Advances in Computational Design
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• v.8 no.2
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• pp.97-112
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• 2023

The Finite Element (FE) modeling of Reinforced Concrete (RC) under seismic loading has a sensitive impact in terms of getting good contribution compared to experimental results. Several idealized model types for simulating the nonlinear response have been developed based on the plasticity distribution alone the model. The Continuum Models are the most used category of modeling, to understand the seismic behavior of structural elements in terms of their components, cracking patterns, hysteretic response, and failure mechanisms. However, the material modeling, contact and nonlinear analysis strategy are highly complex due to the joint operation of concrete and steel. This paper presents a numerical simulation of a chosen RC column under monotonic and cyclic loading using the FE Abaqus, to assessthe hysteretic response and failure mechanisms in the RC columns, where the perfect bonding option is used for the contact between concrete and steel. While results of the numerical study under cyclic loading compared to experimental tests might be unsuccessful due to the lack of bond-slip modeling. The monotonic loading shows a good estimation of the envelope response and deformation components. In addition, this work further demonstrates the advantage and efficiency of the damage distributions since the obtained damage distributions fit the expected results.