Since the National Seismic Hazard Maps for Japan was released in 2009, it has been improved until the latest version in 2020. In this paper, we analyzed the fluctuations in the number of earthquakes calculated from the seismic activity models for the first 2009 edition, the greatly improved 2014 edition, and the latest 2020 edition. As a result, we confirmed the validation of the seismic activity model in 2020. On the other hand, we pointed out the need to improve the seismic activity modeling of large-scale earthquakes.

In order to construct a non-ergodic GMPE (Ground Motion Prediction Equation), we investigated a non-ergodic anomalous seismic intensity term and an attenuation model of GMPE using the flatfile (Morikawa et al., 2023) composed of data from K-NET and KiK-net. The GMPE includes an anomalous intensity term for each site. As a result, this term tends to be negative on the back-arc side, as shown in previous studies, but there are some regional characteristics. Applying the generally used attenuation term to the observed data, predicted values were underestimated in short distances. We reconstructed the attenuation term in order to reduce the bias between the observed and predicted values. The general model of the distance decay term showed a bias in the residuals between observed and predicted values to underestimate them at short distances, and the model of the distance decay term was revised.

In general, when seismometers installed along railway observe earthquake ground motions that exceed predetermined threshold value, facilities in predetermined sections are inspected to confirm safety. During the June 18, 2018, in the Northern Osaka Prefecture Earthquake, inspections were issued for wide sections and many trains suspended between stations were unable to move until the inspections were completed. Safety and convenience can be improved if trains suspended between stations were able to move to the next station. Therefore, it is desirable to provide information that supports decision-making for mobility judgments. To address this issue, we developed a method to score the safety of facilities in each section using Bayesian method, based on the experienced earthquake ground motions along the railway and damage histories accumulated whenever an earthquake occurs. In this paper, we propose how to evaluate safety scores and how to apply this information to railway operations after earthquakes.

The current seismic design doesn't require the time-history response analysis for high-rise buildings with height of at most 60 meters, and the safety verification is practiced by the lateral load-carrying capacity calculation or the limit strength calculation. Although the former conventional calculation is still popular in Japan, it doesn't explicitly evaluate the buildings drift responses to the design spectra representing extremely rare earthquakes. Therefore, in this study, the time-history response analysis was performed on multiple high-rise RC buildings designed based on the lateral load-carrying capacity calculation in the OS1 and OS2 areas on the Osaka Plain, and mainly the drift responses were evaluated. The present paper mainly discusses the relationships between several building specifications and drift responses based on the analytical results.

In past earthquake disasters, damage caused by non-structural elements, furniture and fixtures in indoor spaces had caused human damage and economic damage as well as the loss of functionality of facilities. Therefore, sufficient verification and countermeasures are needed not only for the seismic resistance of structures, but also for the functional maintenance performance of indoor spaces during earthquakes. As a result, research has been conducted focusing on earthquake damage caused by indoor non-structural elements, furniture and fixtures other than structural components of buildings. Evaluation experiment results of indoor space using E-Defense are reported.

The Iwaki Radio Telegraph Station was opened by the Ministry of Telecommunications in 1921 as the first radio telegraph station exclusively for the public between Japan and the United States. The huge facility was installed at the Haramachi Transmitting Station and operated from the Tomioka Receiving Station 30 km to the south. The station is commonly known as Haramachi Radio Tower, which refers to the 200-meter-high reinforced concrete main tower among a group of antennas, but this paper uses "Haramachi Radio Tower" as a symbol of the station and a series of facilities. The Great Kanto Earthquake occurred roughly two years after the station was opened. The damage to Yokohama was immediately transmitted from the "Haramachi Radio Tower" via the Port of Yokohama to the Choshi Coastal Station, and then to radio telegraph stations on the West Coast of the United States. This allowed a great deal of support from overseas to reach Japan, but this feat is being forgotten today. Therefore, we reevaluated it after clarifying the actual role played by the "Haramachi Radio Tower" in the Great Kanto Earthquake.

The shape of the restoring force-story drift angle relationship curve (hysteresis loop) derived from the seismic response data of a building changes depending on the structural health of the building. In this study, we utilized this characteristic for structural health monitoring and proposed a method to assess the risk of collapse due to future earthquake motions based on hysteresis loop images using a convolutional neural network (CNN). We investigated the impact of axis range and resolution settings in the proposed method, comparing the accuracy and recall of the unsafe model in each case. By adjusting the lower limit for the maximum input acceleration of the seismic wave, we achieved a recall of approximately 90% for the unsafe model. Therefore, it can be concluded that the limit of the maximum input acceleration is one of the most influential parameters in damage classification using CNN.

When considering earthquake disaster prevention, it is important to understand the subsurface structure of the area with a high degree of accuracy. In general, accurate subsurface structure estimation requires high-density borehole data. However, the low density of borehole data in regional cities makes it difficult to create a highly accurate subsurface structure model. Recently, technological progress has been made in estimating the subsurface structure using microtremors observations. Therefore, here we attempted to estimate the three-dimensional subsurface structure with high accuracy by combining borehole data and microtremors data. The validity of the estimated subsurface structure was confirmed in terms of topography and amplification characteristics.

Predicting the location of surface faults is essential for countermeasures against surface fault displacement. However, it is difficult to estimate the location of secondary faults that accompany earthquake fault activity. Because the secondary faults are caused by the rupture of the rock mass near the ground surface, it is possible to estimate the secondary fault activity by evaluating the seismic stress of the rock mass in shallow areas. In this paper, we have evaluated the area of occurrence of the secondary faults using the local safety factor, which is defined by the ratio of stress to strength, calculated by the elastic theory of dislocations.

In the author's previous study, a quasi-static loading test was conducted to clarify the effects of non-structural flat walls on the structural performance of a model frame representing the lower 2.5 stories of high-rise RC buildings, which showed that the walls contributed to increasing the frame's shear strength. This paper aims to investigate the interactions between the non-structural flat walls and the main frame via numerical analysis. Two-dimensional finite element method was adopted to reproduce the behavior of the test specimen. The analytical results adequately captured the load-deformation relationship and failure behavior, validating the analytical modeling.