Japan Earthquake Research Articles

Optimizing Weibull Distribution Parameters for Improved Earthquake Modeling in Japan: A Comparative Approach

The Weibull distribution is considered one of the important distributions used in reliability and in the distribution of survival times and in neutrosophic prediction. This paper contained an estimate of a two-parameter Weibull distribution using three estimation methods. One of these methods for estimating parameters is the traditional method, which represents the estimation of the greatest possibility, and the other two methods are estimation using the sine algorithm. and cosine (SCA) and the Ant Colony Algorithm (ACO). The simulation method was used to compare the methods, and it was found that the best method for estimating the parameters of the Weibull distribution is the sine and cosine algorithm (SCA) method. Then, real data was used, represented by the intensity of the earthquake in Japan (Richter) for the period July 1, 2023, to July 16, 2023, to estimate the rate of earthquake intensity in Japan, since Japan is one of the countries most exposed to earthquakes, and it was shown from The results are that the average magnitude of the earthquake in Japan in the period studied is 3.328593, which can be said. Weak buildings may be greatly damaged, but strong buildings are not greatly damaged. Also, a neutrosophic simulation of the same set of data will be suggested for future applications.

Broadband source model of the 2021 MW 7.1 Fukushima‐ken Oki earthquake in Japan based on seafloor and onshore strong‐motion records

AbstractThe 2021 MW 7.1 Fukushima‐ken Oki earthquake was the largest down‐dip compressional intraslab earthquake since August 2016, which is when S‐net records from the seafloor started to be provided. In this study, the empirical Green's function method was used with strong‐motion records from S‐net on the seafloor and KiK‐net onshore to estimate the broadband (0.2–10 Hz) source model of this earthquake. Three strong‐motion generation areas (SMGAs) with very high stress drops were estimated around the edge of the fault. One SMGA with a stress drop of 125 MPa was located in the oceanic crust in the shallow part of the Pacific Plate. The other two SMGAs with stress drops of 313 and 188 MPa were located in the deep part where previous source models without S‐net estimated a small slip. The two deep SMGAs increased the contribution of S‐net to more than that of KiK‐net. The short‐period spectral level was as high as that of the 2011 MW 7.1 Miyagi‐ken Oki earthquake, which was also a down‐dip compressional intraslab earthquake. The estimated broadband source model simulated the horizontal and vertical motions well at stations within 200 km of the hypocenter, except for surface waves at a few S‐net stations.

Individual Preparedness for Large-scale Earthquakes among International Students in Japan: A Cross-sectional Questionnaire Survey.

Individual preparedness for large-scale earthquakes is essential for safety and security in Japan, where earthquakes frequently occur. Foreign residents in Japan face barriers to gathering disaster information, and international students are likely to be more vulnerable to the effects of earthquakes due to the shorter duration of their stay in Japan. However, no studies have been conducted on international students' individual preparedness for large-scale earthquakes in Japan. This study aimed to investigate individual preparedness for large-scale earthquakes among international students in Japan. This cross-sectional study was conducted from May to August 2023 among 360 international students aged ≥20 years enrolled at seven Japanese-language educational institutions in Osaka, Kyoto, and Hyogo prefectures. Of these, 120 (33.3%) agreed to participate in the mail surveys. Students with invalid answers were excluded and 114 (31.7%) were included in the analysis. The information obtained using a self-administered questionnaire included participants' characteristics, methods used to collect information on individual preparedness for large-scale earthquakes (information sources and languages), and individual preparedness for large-scale earthquakes. Many international students had not implemented safety measures at home and lacked information about safety confirmation, evacuation sites and routes, items to wear during evacuation, items to take in case of evacuation, or items to stockpile at home. In particular, approximately half of the participants lacked knowledge about nearby evacuation sites, and only 37.7% had confirmed their evacuation routes to nearby evacuation sites. Only 32.5% had prepared bags containing emergency items to take in case of an evacuation, and most had not packed the items, even though they were stocked at home. In addition, only 8.8% had stockpiled radios and emergency portable toilets at home. It is necessary to promote individual preparedness for large-scale earthquakes among international students in Japan.

Gender Differences in the Association between Psychological Distress and Sociability among Older Adult Survivors: Cross-Sectional Survey Four Years after the 2016 Kumamoto Earthquake in Japan.

Mental health deterioration after a disaster is a concern. Individuals' sociability is expected to relate to the risk of this deterioration; however, research focusing on older adults is lacking. We aimed to investigate the relationship between psychological distress and sociability in older adults who survived the 2016 Kumamoto earthquake. We conducted a self-reported questionnaire survey in 2020. Data on 3,588 people aged 65 years and over (2,024 women and 1,564 men, mean age 74.6 ± 7.2, mean ± standard deviation) were analyzed. The overall prevalence of psychological distress (the Kessler psychological distress scale: K6 ≧ 10) was 10.5%; by gender, it was 11.2% in women and 9.5% in men. Logistic regression analysis revealed that, in the total sample, age, gender, public housing, reduction in income resulting from the coronavirus disease 2019 pandemic, self-rated unhealthy conditions, subjective social isolation, and a lack of awareness of community events were positively associated with psychological distress. For women, a lack of community participation was positively related to psychological distress. For men, not knowing the change in school district after relocation was negatively associated with psychological distress, probably due to men's scarce community participation and reliance on friendships, compared to women's stronger dependence on community. Moreover, having a family member or friend to consult with was associated with a lower risk of psychological distress, regardless of gender. Gender differences were related to different conditions of social participation and types of social relationships. Enhancing community participation and family relationships among women and social contact with friends among men is essential.

A Corpus-Based Comparative Study on Chinese and Japanese Earthquake Reports

A Corpus-Based Comparative Study on Chinese and Japanese Earthquake Reports

Analysis of GPS TEC anomalies associated with Mw > 7 earthquakes in Japan

The Global Positioning System (GPS) provides insights into the Earthquakes (EQs) ionospheric anomalies. Different space-and-ground parameters are used to observe EQ precursors. This paper uses the Total Electron Content (TEC) from nearby operating GPS stations to detect perturbation in the ionosphere before and after four EQs in Japan in 2011. In addition, the TEC variations in relation to the depth and magnitude of the EQs are noticed. The analysis shows significant variations in TEC to depth and magnitude in association with each main shock. TEC value abruption starts on 8 March and continues for 6 days in March. In April, TEC abnormalities start 5 days before and after the man shock. The geomagnetic Kp index is higher than four from March 10 to 12. The anomalies in this study are clearly associated with geomagnetic storms, as the Kp index is active. Moreover, the Dst index is below the negative 50 (nT) in the seismic period of March and April. The ionosphere parameters will define the severity of seismic activity in future.

On the fragility of non‐structural elements in loss and recovery: Field observations from Japan

AbstractThe role of non‐structural elements (NSEs) in the seismic performance of buildings has been highlighted in past years. Research studies following state‐of‐the‐art methodologies generally find that when the structural collapse is not of significant concern, NSEs tend to dominate the repair costs and financial investment required in a building. This paper examines field observations from interviews and data collected from commercial buildings via structural health monitoring (SHM) following the 2018 Osaka earthquake in Japan. It suggests that fragility functions used in current methodologies for estimating NSE damage may not be entirely representative of the in‐situ reality and possibly underestimate actual damage. Additionally, interviews with building owners/managers indicate that the alarm and financial impact of NSEs was not as critical as anticipated, with much of the observed NSE damage not of serious concern and tolerable in many cases. This article provides discussion and insight into possible causes for these differences before discussing how current methodologies can benefit from these observations. It is believed that many of the fragility functions currently used to estimate NSE damage may not be representative because of differences in installation conditions and loading protocols used in experimental testing, possible interaction with other elements, variability in the quality of workmanship during installation and possible wear, tear and degradation during service. On the other hand, it is seen how SHM data recorded during seismic events may provide valuable data for an alternative means to develop fragility functions. Furthermore, it is seen that when building recovery states (RSs) other than the implicitly assumed ‘full recovery’ state used in guidelines like FEMA P‐58 are explored, the role of NSEs in direct monetary losses significantly reduces. This coincides with the field observations in Japan regarding the impact of NSEs and supports the recent developments in functional recovery on what building owners and occupants are prepared to tolerate post‐earthquake. It indicates that when discussing the relative importance of different building performance groups, it is vital that the expected RS is also stated, as for most decision‐makers following major events, functionality rather than full recovery remains the primary goal; hence, repairs and proactive measures should bear this in mind for more effective use of resources.

Ground motion prediction model for shallow crustal earthquakes in Japan based on XGBoost with Bayesian optimization

Ground motion prediction is an important and complex research subject in earthquake engineering and traditional approaches based on statistical regression have much room for improvement in prediction accuracy. Utilizing the 67,164 ground motion records from KiK-net and K-Net for 777 shallow crustal earthquakes between 1997 and 2019 in Japan, this paper proposes a ground motion prediction model XGBoost-SC based on the machine learning algorithm of eXtreme Gradient Boosting (XGBoost) for Japan. Magnitude, focal depth, hypo-central distance, Vs30, site altitude, and focal mechanism were used as the feature parameters, and XGBoost, Random Forest, and Deep Neural Networks (DNN) algorithms were selected for model training while Bayesian optimization was used to search for optimized hyperparameters to improve the prediction accuracy. XGBoost algorithm was selected for further study based on the comparison of results from the three algorithms. Residual change with magnitude and hypo-central distance, the probability distribution of residuals, residual standard deviation (σ), residual mean squared error (MSE), and Pearson correlation coefficient (R) were used as the evaluation parameters, and a comparison study was performed against the ground motion prediction equation based on traditional approaches. Actual earthquake events were selected to compare the prediction results against the observation records. To further validate and explain the proposed model, SHapley Additive exPlanations (SHAP) analysis was performed to explain the impact of selected feature parameters on the proposed model. The results demonstrate that the proposed XGBoost-SC model has good prediction stability for all periods, and its residual errors are smaller than those of other models. Therefore, the proposed model can better reflect the ground motion attenuation for shallow crustal earthquakes in Japan and can serve as a better model for ground motion prediction in future aseismic design and earthquake disaster mitigation efforts.

Ground motion prediction equations for the horizontal component from shallow crustal and upper mantle earthquakes in Japan using site period as site parameter

Ground motion prediction equations for the horizontal component from shallow crustal and upper mantle earthquakes in Japan using site period as site parameter

Offshore near-fault pulse-like ground motions: An insight into the DONET1 seafloor ground motions from the 2016 Mw6.0 Off-Mie earthquake in Japan

Offshore near-fault ground motions were obtained by the DONET1 seafloor seismic network during the 2016 Off-Mie Mw6.0 earthquake that occurred in the Nankai Trough of Japan. These data provide an opportunity for exploring the characteristics of offshore near-fault ground motions, especially pulse-like ground motions. A comparison of the offshore and onshore near-fault ground motions indicates that the recorded offshore spectral acceleration (SA) in the period of 0.5–5.0 s and peak ground velocity (PGV) for this earthquake are higher than those of the onshore values, and the observed maximum spectral value (βmax) of the offshore near-fault ground motions in this event is underestimated by the design spectra in the seismic codes of China, the United States, and Japan. Based on the Hilbert-Huang transform method, eight offshore pulse-like ground motion records are identified and extracted in the Off-Mie earthquake. The primary analysis indicates that the pulse-like ground motion may be caused by the directivity effect and the radiation pattern. Comparing the pulse parameters, time-frequency parameters, and response spectra of offshore and onshore pulse-like ground motions, the findings demonstrate that within the context of this earthquake event, approximately half of the offshore pulse amplitude (Vp) exceeds the predicted values of onshore models; the low-frequency components of offshore pulse-like ground motions of this event are more pronounced, constituting a larger portion of the total ground motion energy; offshore pulse-like ground motions exhibit a tendency to possess higher maximum instantaneous energy (Einst) compared to onshore pulse-like ground motions with similar rupture distances. Moreover, the βmax of offshore pulse-like ground motions is found to be greater than that of onshore pulse-like ground motions in medium to long periods (>0.5 s). The identified and characteristic recognition of offshore near fault pulse-like ground motion revealed by this earthquake event raises new concerns about seismic design for offshore engineering.

Post-earthquake fire ignition model uncertainty in regional probabilistic shaking–fire cascading multi-hazard risk assessment: A study of earthquakes in Japan

Fires following earthquakes have significant impact on urban communities in earthquake-prone countries with wooden buildings, in addition to the main earthquake hazard of ground shaking. Regional-scale post-earthquake fire risk assessments are important for developing effective risk reduction strategies. Such risk assessments require the consideration of epistemic uncertainty, that is, uncertainty caused by lack of knowledge concerning the best models, in addition to aleatoric uncertainty. This study focused on epistemic uncertainty in post-earthquake fire ignition estimations, and incorporated it into risk assessments by using alternative empirical ignition models. The key objectives of this study were as follows: (1) correlating the probability of ignition per person to the ground motion intensity based on data for different past large earthquakes in Japan; (2) investigating the impact of using ignition models calibrated on different earthquake events in risk assessments through a realistic case study considering possible large earthquakes. A hierarchical Bayesian Poisson regression analysis revealed that the empirical relationship between the ignition probability and ground motion intensity greatly varies across six major large earthquakes in Japan from 1995 to 2022. Particularly, the effects of ignition prevention measures that have been widely implemented in households since the 1995 Kobe earthquake were inferred from much smaller ignition probabilities in approximately the last 10 years. The effects of this high epistemic uncertainty manifested as the large variability of the loss exceedance curve for a portfolio of buildings. These results indicate that the new ignition models can help to foster risk-informed decision-making under epistemic uncertainty.

A Damping Modification Factor Prediction Model for Horizontal Displacement Spectrum from Shallow Crustal and Upper-Mantle Earthquakes in Japan Accounting for Site Conditions

ABSTRACT This article presents damping modification factors (DMFs) for the horizontal component of the strong-motion records generated by the shallow crustal and upper-mantle earthquakes in Japan. This model can be used to scale a 5% damped design spectrum that does not associate with a known magnitude and rupture distance to obtain a design spectrum with the desirable damping ratios. Our previous study suggested that the site effect on DMF was significant, and we used site class as the site-effect parameter. We used a quadratic function of damping ratio in a natural logarithm scale to model the effect of damping ratios and we used fourth-order polynomials of the natural logarithm spectral period to present the effect of the spectral period when the spectral period is over 0.06 s. The between-event, between-site, and within-site standard deviations can be described by the linear function of the damping ratio in a natural logarithm scale. The between-event standard deviations are smaller than the within-event standard deviations and the between-site standard deviations are less than the within-site ones at many spectral periods. Reasonable displacement spectra can be obtained by using the DMF model from this study to scale the 5% damped displacement spectra. The differences in the DMF values from the three types of earthquakes are moderate at many spectral periods and the predicted DMF values from this study are similar to those from other studies at some spectral periods, but the differences are considerable at the other spectral periods. The variation trend of the DMF values suggests that the predicted DMF values may reach the theoretic value of 1.0 at some spectral periods over 5.0 s. Residual distribution analysis suggested that the bilinear function of magnitude and fault-top depth can be used in a model for scenario earthquakes.

Activities and roles of mosques in Japan after the recent major earthquakes: A comprehensive study

As minority groups, foreign nationals are considered vulnerable because of cultural, linguistic, and religious differences; however, some may work as critical stakeholders in disaster risk reduction (DRR). In Japan, some mosque communities (mainly composed of foreign nationals) were engaged in relief activities immediately after disasters; however, these reports were scattered and did not clarify long-term activities. Therefore, we aimed to summarize the activities and roles of mosques located in areas affected by recent natural hazard-related disasters in the short (that is, response) and long term (that is, recovery and mitigation). We targeted three mosques located in areas affected by the 2011 Great East Japan Earthquake, and the 2016 Kumamoto Earthquake in Japan. We conducted a literature review and interviewed mosque administrators. The results showed that all mosques worked as distribution centers in the short term, receiving relief supplies from Muslims all over Japan and distributing them to affected people. The relief goods included halal foods that fit foreign minorities, but these goods were distributed not only to them but also to other people regardless of religion and nationality. Some mosques also functioned as evacuation shelters, soup kitchens, and accommodations for volunteers. Support for affected people was further facilitated by intermediaries (such as private organizations and key local individuals) between the mosques and local communities or governments. In contrast to the short term, we did not find prominent recovery and mitigation activities by the mosques. These comprehensive findings contribute to the promotion of inclusive and community-based DRR activities.

Reconsideration of Urbanization in Tokyo Metropolitan Area Since 1923 Great Kanto Earthquake from the Perspective of Exposure

The year 2023 marks the 100th commemoration of the disastrous Kanto Earthquake in Japan, which shattered the urban fabric of Tokyo and other southern prefectures. In the years following 1923, much research into disaster risk reduction (especially fire prevention) was undertaken. This study evaluated research trends and the impact of the earthquake on the city using metropolitan population data. The following is reported: (1) This study summarized English and Japanese academic papers and reports on the Great Kanto Earthquake that have been published over the last 100 years. (2) The area of fire spread and number of damaged buildings in Tokyo due to the Great Kanto Earthquake were overwhelmingly larger than those in other areas. (3) The difference in the relative amount of damage caused by natural disasters with more than 1,000 death toll to the annual national budget in Japan became clear. (4) The Great Kanto Earthquake was the only natural disaster that caused a net worth of damage exceeding the Japanese national budget by 3.8 times. (5) The expansion of the Tokyo metropolitan area over the 100 years since the Great Kanto Earthquake was visually clarified based on demographics. (6) Today, many people live densely on soft ground, with an amplification factor of 1.8 or higher, which is 23.0% of the total population.

Strong Ground Motion of the 1923 Kanto, Japan Earthquake

The 1923 Kanto earthquake (MJ=7.9) has great significance for seismic hazard assessments of the Tokyo metropolitan area, because it caused extensive damage to the area. To deepen our understanding of the strong ground motion of the Kanto earthquake, this paper reviewed studies on its observed strong ground motion and found that 1) seismic intensity VI on the Japanese scale (IX or X on the M. M. scale) was widely distributed in an area of approximately 8,000 km2, which is equivalent of that of the 2011 M9 Tohoku earthquake, 2) strong effects of soil amplification on ground motion were suggested by the correlation of the damage distribution with surface geology, 3) the restoration of the scaled-out seismogram indicated that the ground motion at the upland of Tokyo would be roughly 50 cm/s for maximum velocity and 50 cm for maximum displacement, and 4) the ground motion in the epicentral area is unclear, but would be roughly twice or more as strong as that at Tokyo.

On the use of tsunami-source data for high-resolution fault imaging of offshore earthquakes

The source imaging for offshore earthquakes using terrestrial geodetic data has a limited estimation performance due to the low data resolution. One approach to overcome this limitation is the use of seafloor geodetic data. In this study, we focus on tsunami-source data, which is the spatial distribution of vertical crustal displacements above the source area and can be derived from tsunami waveform records. We evaluate how the use of this spatial seafloor geodetic data improves the estimation of a rectangular fault model. Here, the fault model of the 2016 off-Fukushima earthquake in Japan, which was a shallow intraplate earthquake (Mw 7.0), was estimated by three inversions: terrestrial Global Navigation Satellite System (GNSS) data only, tsunami-source data only, and a combination of the GNSS data and tsunami-source data. A Bayesian inversion approach was used to understand the distribution of the estimated fault parameters and their relationship. The results indicated that the terrestrial GNSS data have a low resolution for the analysis of the offshore earthquake, which resulted in a biased solution with large uncertainty. Conversely, the use of tsunami-source data significantly improved the resolution and reliability of source imaging and reduced the dependency among fault parameters. These results suggested that the high-spatial-resolution information of tsunami source is a powerful tool in source imaging of offshore shallow earthquakes. Moreover, the combined use of the two different geodetic data leads to a more robust estimation of fault parameters. We believe that the use of tsunami-source data is useful, not only for the post hoc source analysis, but also for estimating an earthquake rupture area just after a large earthquake, where GNSS data are currently used.Graphical

Probabilistic Liquefaction Assessment Based on an In-situ State Parameter Considering Soil Spatial Variability and Various Uncertainties

The state parameter (ψ) is based on a framework of critical state soil mechanics, which reflects the influences of soil compactness and stress level and has significant advantages for liquefaction analysis. In engineering practice, a simplified procedure based on the cone penetration test (CPT) to assess the liquefaction potential in the field involves model and parameter uncertainties. Furthermore, the use of limited CPT measurements involves project-specific test uncertainties, and the spatial variability of soil properties has a remarkable effect on soil liquefaction. To tackle these challenges, this study develops a ψ-based liquefaction probability framework to integrate the prior information of project-specific CPT, and uses limited tests to characterize the 2D spatial distribution of liquefaction potential with proper consideration of various uncertainties and soil spatial variability. The framework is developed based on simulation of Gaussian stationary random fields and Markov Chain Monte Carlo simulation. The proposed method is demonstrated using real CPT data from the 2011 Tohoku-Oki earthquake in Japan. The results indicate that the ψ-based evaluation performs well and can reasonably assess the liquefaction phenomenon of heterogeneous soils. This study incorporating the spatial variability of ψ into the liquefaction probability framework provides valuable information for geotechnical engineering design.

New ground-motion prediction equations for significant duration of subduction intraslab and interface earthquakes in Japan

New ground-motion prediction equations for significant duration of subduction intraslab and interface earthquakes in Japan

Soil‐water response in a volcanic ash hillslope affected by fissures and microtopographic changes caused by the Kumamoto earthquake, in Japan

AbstractWe examined soil‐water response in a hillslope with multi‐layered volcanic soils affected by fissures formed by intense shaking during the 2016 Kumamoto earthquake in Japan. Pressure head and volumetric water content responses in a 6 × 20 m hillslope ridgeline plot were monitored by tensiometers and capacitance‐based soil moisture sensors, respectively. The plot contained seven seismic fissures (0.3–0.8 m deep and 0.4–2.2 m wide) formed parallel to the ridgeline that exposed underlying soil layers, while areas with topsoil occurred between the fissures. Among the alternating layers, the andisol (ca. 1.0 m deep) consistently experienced high pressure heads (>−150 cm H2O) and volumetric water contents (>0.58 cm3 cm−3), indicating high water‐holding capacity. This andisol was a key layer for storing soil water and causing slow drainage into the deeper matrix, resulting in abrupt increases in volumetric water content during storms. Rainwater directly reaching the bottom of fissures without percolating through the topsoil caused rapid soil‐water response compared to the soil layer where water percolated via topsoil. Analysis of in‐situ soil water retention curves, recession rates and water storage changes revealed that the second andisol had unique characteristics for retaining water in the hillslope. The findings of this study show that spatial and temporal variability of soil water responses varied associated with earthquake‐induced fissure formation and soil water characteristics of multi‐layered volcanic soils.

Modeling uncertainty of specimens employing spines and force‐limiting connections tested at E‐defense shake table

AbstractIn light of the significant damage observed after earthquakes in Japan and New Zealand, enhanced performing seismic force‐resisting systems and energy dissipation devices are increasingly being utilized in buildings. Numerical models are needed to estimate the seismic response of these systems for seismic design or assessment. While there have been studies on modeling uncertainty, selecting the model features most important to response can remain ambiguous, especially if the structure employs less well‐established lateral force‐resisting systems and components. Herein, a global sensitivity analysis was used to address modeling uncertainty in specimens with elastic spines and force‐limiting connections (FLCs) physically tested at full‐scale at the E‐Defense shake table in Japan. Modeling uncertainty was addressed for both model class and model parameter uncertainty by varying primary models to develop several secondary models according to pre‐established uncertainty groups. Numerical estimates of peak story drift ratio and floor acceleration were compared to the results from the experimental testing program using confidence intervals and root‐mean‐square error. Metrics such as the coefficient of variation, variance, linear Pearson correlation coefficient, and Sobol index were used to gain intuition about each model feature's contribution to the dispersion in estimates of the engineering demands. Peak floor acceleration was found to be more sensitive to modeling uncertainty compared to story drift ratio. Assumptions for the spine‐to‐frame connection significantly impacted estimates of peak floor accelerations, which could influence future design methods for spines and FLC in enhanced lateral‐force resisting systems.