• Title/Summary/Keyword: Earthquake prediction

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Comparison of Liquefaction Assessment Results with regard to Geotechnical Information DB Construction Method for Geostatistical Analyses (지반 보간을 위한 지반정보DB 구축 방법에 따른 액상화 평가 결과 비교)

  • Kang, Byeong-Ju;Hwang, Bum-Sik;Bang, Tea-Wan;Cho, Wan-Jei
    • Journal of the Korean Geotechnical Society
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    • v.38 no.4
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    • pp.59-70
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    • 2022
  • There is a growing interest in evaluating earthquake damage and determining disaster prevention measures due to the magnitude 5.8 earthquake in Pohang, Korea. Since the liquefaction phenomena occurred extensively in the residential area as a result of the earthquake, there was a demand for research on liquefaction phenomenon evaluation and liquefaction disaster prediction. Liquefaction is defined as a phenomenon where the strength of the ground is completely lost due to a sudden increase in excess pore water pressure caused due to large dynamic stress, such as an earthquake, acting on loose sand particles in a short period of time. The liquefaction potential index, which can identify the occurrence of liquefaction and predict the risk of liquefaction in a targeted area, can be used to create a liquefaction hazard map. However, since liquefaction assessment using existing field testing is predicated on a single borehole liquefaction assessment, there has been a representative issue for the whole targeted area. Spatial interpolation and geographic information systems can help to solve this issue to some extent. Therefore, in order to solve the representative problem of geotechnical information, this research uses the kriging method, one of the geostatistical spatial interpolation techniques, and constructs a geotechnical information database for liquefaction and spatial interpolation. Additionally, the liquefaction hazard map was created for each return period using the constructed geotechnical information database. Cross validation was used to confirm the accuracy of this liquefaction hazard map.

Groundwater Level Responses due to Moderate·Small Magnitude Earthquakes Using 1Hz groundwater Data (1Hz 지하수 데이터를 활용한 중·소규모 지진으로 인한 지하수위 반응)

  • Gahyeon Lee;Jae Min Lee;Dongkyu Park;Dong-Hun Kim;Jaehoon Jung;Soo-Hyoung Lee
    • Journal of Soil and Groundwater Environment
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    • v.29 no.4
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    • pp.32-43
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    • 2024
  • Recently, numerous earthquakes have caused significant casualties and property damage worldwide, including major events in 2023 (Türkiye, M7.8; Morocco, M6.8) and 2024 (Noto Peninsula, Japan, M7.6; Taiwan, M7.4). In South Korea, the frequency of detectable and noticeable earthquakes has been gradually increasing since the M5.8 Gyeongju Earthquake. Notable recent events include those in Jeju (M4.9), Goesan (M4.1), the East Sea (M4.5), and Gyeongju (M4.0) since 2020. This study, for the first time in South Korea, monitored groundwater levels and temperatures at a 1Hz frequency to observe the responses in groundwater to moderate and small earthquakes primarily occurring within the country. Between April 23, 2023, and May 22, 2023, 17 earthquakes were reported in the East Sea region with magnitudes ranging from M2.0 to M4.5. Analysis of groundwater level responses at the Gangneung observation station revealed fluctuations associated with five of these events. The 1Hz observation data clearly showed groundwater level changes even for small earthquakes, indicating that groundwater is highly sensitive to the frequent small earthquakes recently occurring in South Korea. The analysis confirmed that the maximum amplitude of groundwater level changes due to earthquakes is proportional to the earthquake's magnitude and the distance from the epicenter. These findings highlight the importance of precise 1Hz-level observations in earthquake-groundwater research. This study provides foundational data for earthquake monitoring and prediction and emphasizes the need for ongoing research into monitoring the changes in groundwater parameters (such as aquifer characteristics, quantity/quality, and contaminant migration) induced by various magnitudes of earthquakes that may occur within the country in the future.

Advanced and Application of Onsite EEW Technology in Korea (국내에서의 지진현장경보 기술 고도화 및 적용)

  • Lee, Ho Jun;Jeon, Inchan;Seo, Jeong Beom;Lee, Jin Koo
    • Journal of the Society of Disaster Information
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    • v.16 no.4
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    • pp.670-681
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    • 2020
  • Purpose: This study aims to derive a PGV prediction equation and to enhance the application of the Onsite EEW technology which has developed through previous studies. Method: The prediction equation for the Onsite EEW derived from earthquake data M≥3.0 and MMI≥II over the past four years. Local seismic risk is estimated using M and PGV deduced from P wave properties. Result: The improved PGV prediction equation estimated the MMI with an average accuracy of 94.8% and the 𝜏c : Pd method also showed valid performance for alerting local seismic risks. Conclusion: Onsite EEW technology is successfully applied to Korea, and becomes to reduce the blind zone to about 14km.

Improved prediction of soil liquefaction susceptibility using ensemble learning algorithms

  • Satyam Tiwari;Sarat K. Das;Madhumita Mohanty;Prakhar
    • Geomechanics and Engineering
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    • v.37 no.5
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    • pp.475-498
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    • 2024
  • The prediction of the susceptibility of soil to liquefaction using a limited set of parameters, particularly when dealing with highly unbalanced databases is a challenging problem. The current study focuses on different ensemble learning classification algorithms using highly unbalanced databases of results from in-situ tests; standard penetration test (SPT), shear wave velocity (Vs) test, and cone penetration test (CPT). The input parameters for these datasets consist of earthquake intensity parameters, strong ground motion parameters, and in-situ soil testing parameters. liquefaction index serving as the binary output parameter. After a rigorous comparison with existing literature, extreme gradient boosting (XGBoost), bagging, and random forest (RF) emerge as the most efficient models for liquefaction instance classification across different datasets. Notably, for SPT and Vs-based models, XGBoost exhibits superior performance, followed by Light gradient boosting machine (LightGBM) and Bagging, while for CPT-based models, Bagging ranks highest, followed by Gradient boosting and random forest, with CPT-based models demonstrating lower Gmean(error), rendering them preferable for soil liquefaction susceptibility prediction. Key parameters influencing model performance include internal friction angle of soil (ϕ) and percentage of fines less than 75 µ (F75) for SPT and Vs data and normalized average cone tip resistance (qc) and peak horizontal ground acceleration (amax) for CPT data. It was also observed that the addition of Vs measurement to SPT data increased the efficiency of the prediction in comparison to only SPT data. Furthermore, to enhance usability, a graphical user interface (GUI) for seamless classification operations based on provided input parameters was proposed.

Uniform Hazard Spectrum for Seismic Design of Fire Protection Facilities (소방시설의 내진설계를 위한 등재해도 스펙트럼)

  • Kim, Jun-Kyoung;Jeong, Keesin
    • Fire Science and Engineering
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    • v.31 no.1
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    • pp.26-35
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    • 2017
  • Since the Northridge earthquake (1994) and Kobe earthquake (1995), the concept of performance-based design has been actively introduced to design major structures and buildings. Recently, the seismic design code was established for fire protection facilities. Therefore, the important fire protection facilities should be designed and constructed according to the seismic design code. Accordingly, uniform hazard spectra (UHS), with annual exceedance probabilities, corresponding to the performance level, such as operational, immediate occupancy, life safety, and collapse prevention, are required for performance-based design. Using the method of probabilistic seismic hazard analysis (PSHA), the uniform hazard spectra for 5 major cities in Korea with a recurrence period of 500, 1,000, and 2,500 years corresponding to frequencies of (0.5, 1.0, 2.0, 5.0, 10.0)Hz and PGA, were analyzed. The expert panel was comprised of 10 members in seismology and tectonics. The ground motion prediction equations and several seismo tectonic models suggested by 10 expert panel members in seismology and tectonics were used as the input data for uniform hazard spectrum analysis. According to sensitivity analysis, the parameter of spectral ground motion prediction equations has a greater impact on the seismic hazard than seismotectonic models. The resulting uniform hazard spectra showed maximum values of the seismic hazard at a frequency of 10Hz and also showed the shape characteristics, which are similar to previous studies and related technical guides for nuclear facilities.

Predictions of curvature ductility factor of doubly reinforced concrete beams with high strength materials

  • Lee, Hyung-Joon
    • Computers and Concrete
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    • v.12 no.6
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    • pp.831-850
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    • 2013
  • The high strength materials have been more widely used in reinforced concrete structures because of the benefits of the mechanical and durable properties. Generally, it is known that the ductility decreases with an increase in the strength of the materials. In the design of a reinforced concrete beam, both the flexural strength and ductility need to be considered. Especially, when a reinforced concrete structure may be subjected an earthquake, the members need to have a sufficient ductility. So, each design code has specified to provide a consistent level of minimum flexural ductility in seismic design of concrete structures. Therefore, it is necessary to assess accurately the ductility of the beam sections with high strength materials in order to ensure the ductility requirement in design. In this study, the effects of concrete strength, yield strength of reinforcement steel and amount of reinforcement including compression reinforcement on the complete moment-curvature behavior and the curvature ductility factor of doubly reinforcement concrete beam sections have been evaluated and a newly prediction formula for curvature ductility factor of doubly RC beam sections has been developed considering the stress of compression reinforcement at ultimate state. Based on the numerical analysis results, the proposed predictions for the curvature ductility factor are verified by comparisons with other prediction formulas. The proposed formula offers fairly accurate and consistent predictions for curvature ductility factor of doubly reinforced concrete beam sections.

Development of Road Surface Temperature Prediction Model using the Unified Model output (UM-Road) (UM 자료를 이용한 노면온도예측모델(UM-Road)의 개발)

  • Park, Moon-Soo;Joo, Seung Jin;Son, Young Tae
    • Atmosphere
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    • v.24 no.4
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    • pp.471-479
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    • 2014
  • A road surface temperature prediction model (UM-Road) using input data of the Unified Model (UM) output and road physical properties is developed and verified with the use of the observed data at road weather information system. The UM outputs of air temperature, relative humidity, wind speed, downward shortwave radiation, net longwave radiation, precipitation and the road properties such as slope angles, albedo, thermal conductivity, heat capacity at maximum 7 depth are used. The net radiation is computed by a surface radiation energy balance, the ground heat flux at surface is estimated by a surface energy balance based on the Monin-Obukhov similarity, the ground heat transfer process is applied to predict the road surface temperature. If the observed road surface temperature exists, the simulated road surface temperature is corrected by mean bias during the last 24 hours. The developed UM-Road is verified using the observed data at road side for the period from 21 to 31 March 2013. It is found that the UM-Road simulates the diurnal trend and peak values of road surface temperature very well and the 50% (90%) of temperature difference lies within ${\pm}1.5^{\circ}C$ (${\pm}2.5^{\circ}C$) except for precipitation case.

An intelligent semi-active isolation system based on ground motion characteristic prediction

  • Lin, Tzu-Kang;Lu, Lyan-Ywan;Hsiao, Chia-En;Lee, Dong-You
    • Earthquakes and Structures
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    • v.22 no.1
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    • pp.53-64
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    • 2022
  • This study proposes an intelligent semi-active isolation system combining a variable-stiffness control device and ground motion characteristic prediction. To determine the optimal control parameter in real-time, a genetic algorithm (GA)-fuzzy control law was developed in this study. Data on various types of ground motions were collected, and the ground motion characteristics were quantified to derive a near-fault (NF) characteristic ratio by employing an on-site earthquake early warning system. On the basis of the peak ground acceleration (PGA) and the derived NF ratio, a fuzzy inference system (FIS) was developed. The control parameters were optimized using a GA. To support continuity under near-fault and far-field ground motions, the optimal control parameter was linked with the predicted PGA and NF ratio through the FIS. The GA-fuzzy law was then compared with other control laws to verify its effectiveness. The results revealed that the GA-fuzzy control law could reliably predict different ground motion characteristics for real-time control because of the high sensitivity of its control parameter to the ground motion characteristics. Even under near-fault and far-field ground motions, the GA-fuzzy control law outperformed the FPEEA control law in terms of controlling the isolation layer displacement and the superstructure acceleration.

Three-dimensional geostatistical modeling of subsurface stratification and SPT-N Value at dam site in South Korea

  • Mingi Kim;Choong-Ki Chung;Joung-Woo Han;Han-Saem Kim
    • Geomechanics and Engineering
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    • v.34 no.1
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    • pp.29-41
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    • 2023
  • The 3D geospatial modeling of geotechnical information can aid in understanding the geotechnical characteristic values of the continuous subsurface at construction sites. In this study, a geostatistical optimization model for the three-dimensional (3D) mapping of subsurface stratification and the SPT-N value based on a trial-and-error rule was developed and applied to a dam emergency spillway site in South Korea. Geospatial database development for a geotechnical investigation, reconstitution of the target grid volume, and detection of outliers in the borehole dataset were implemented prior to the 3D modeling. For the site-specific subsurface stratification of the engineering geo-layer, we developed an integration method for the borehole and geophysical survey datasets based on the geostatistical optimization procedure of ordinary kriging and sequential Gaussian simulation (SGS) by comparing their cross-validation-based prediction residuals. We also developed an optimization technique based on SGS for estimating the 3D geometry of the SPT-N value. This method involves quantitatively testing the reliability of SGS and selecting the realizations with a high estimation accuracy. Boring tests were performed for validation, and the proposed method yielded more accurate prediction results and reproduced the spatial distribution of geotechnical information more effectively than the conventional geostatistical approach.

Application of the JMA instrumental intensity in Korea (일본 기상청 계측진도의 국내 활용)

  • Kim, Hye-Lim;Kim, Sung-Kyun;Choi, Kang-Ryong
    • Journal of the Earthquake Engineering Society of Korea
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    • v.14 no.2
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    • pp.49-56
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    • 2010
  • In general, the seismic intensity deduced from instrumental data has been evaluated from the empirical relation between the intensity and the PGA. From the point of view that the degree of earthquake damage is more closely associated with the seismic intensity than with the observed PGA, JMA developed the instrumental seismic intensity (JMA instrumental intensity) meter that estimate the real-time seismic intensity from the observed strong motion data to obtain a more correct estimate of earthquake damage. The purpose of the present study is to propose a practical application of the JMA instrumental intensity in Korea. Since the occurrence of strong earthquakes is scarce in the Korean Peninsula, there is an insufficiency of strong motion data. As a result, strong motion data were synthesized by a stochastic procedure to satisfy the characteristics of a seismic source and crustal attenuation of the Peninsula. Six engineering ground motion parameters, including the JMA instrumental intensity, were determined from the synthesized strong motion data. The empirical relations between the ground motion parameters were then analyzed. Cluster analysis to classify the parameters into groups was also performed. The result showed that the JMA acceleration ($a_0$) could be classified into similar group with the spectrum intensity and the relatively distant group with the CAV (Cumulative Absolute Velocity). It is thought that the $a_0$ or JMA intensity can be used as an alternative criterion in the evaluation of seismic damage. On the other hand, attenuation relation equations for PGA and $a_0$ to be used in the prediction of seismic hazard were derived as functions of the moment magnitude and hypocentral distance.