This study examines two different seismic response analysis models of a nuclear power plant building, including the three-dimensional finite-element (3D FE) model with shell elements and the conventional sway-rocking model. Further, the results obtained using these models are compared for estimating the effects related with the differences between the modeling methods. In addition, the authors analyzed the spatial variations of the response results based on the merits of the 3D FE model, and the potential applications of this information are discussed.

We show that the existence of nonlinear site responses of vertical motions is identified by velocity waveforms integrated from acceleration records observed at the ground surface using KiK-net records. In the case of the generation of nonlinear site responses of vertical motions, the velocity time history has a linear trend to the downward direction and then becomes constant or almost constant. In some cases, the velocity time history abruptly becomes constant like as a step function. The surface-to-borehole spectral ratios of vertical strong motions with such features have the peaks at the same or twice of the peak frequencies of the horizontal strong motions. The spectral ratios of vertical strong motions tend to be larger than those of weak motions in the frequency less than about 10 Hz. The peak levels of spectral ratios of horizontal strong motions at half of peak frequencies of vertical strong motions also tend to be larger than those of weak motions. Especially, the vertical motions with constant absolute values Vnon greater than 5 cm/s had relatively clear nonlinear site responses. The strong motion records with three biggest Vnon were equivalent to instrumental seismic intensity scale of 7.

In order to improve the accuracy of empirical ground motion prediction, we examined to make a ground motion prediction model considering spatial variation of path and source effects. A modeling using mixed geographically weighted regression was proposed to model spatial variations of that effects, and the effectiveness of the modeling was examined using data from crustal earthquakes around Fukushima Prefecture. It was confirmed that the proposed modeling could take into account the spatial variations according to the data, and the prediction model with smaller residuals than conventional modeling could be obtained. The proposed modeling is effective to make advanced ground motion prediction model by utilizing increasing data.

It is an urgent issue to build the capabilities for rescue teams for disaster response operations, and efforts has been paid for improving rescue training in Police and Fire departments. For this purpose, detailed information on actual rescue operations are very useful. Aiming to collect detailed information useful for rescue training design and rescue capability building, the authors of this study conducted an extensive survey on the rescue operations of police teams in houses collapsed due to the 2016 Kumamoto earthquakes and clarified the situations and aspects in detail, such as damage grade of buildings which became to be the sites for confined space rescues, locations of victims trapped inside the collapsed houses, the scale and shape configurations of spaces inside the collapsed houses, concrete entrapment situations including whether or not victims were being pressed by heavy objects, actual rescue operations procedures, and duration of each rescue process. We also developed a survey methodology for collecting data on rescue operations inside collapsed wooden houses, including development of interview methods using miniature models to reproduce the rescue site situations and development of space-scale-pattern-chart utilizing the interview results which was included in the questionnaire sheet we developed. As the result, we clarified the actual conditions of rescue operations including building collapse damage grades and site situations of entrapments in concrete quantitative data, which were only grasped in abstract expressions before such as “unstable”, “confined”, “buried”, and so on. Our results include useful findings that could be applied in future rescue operations and training, and also, the questionnaire we developed can be utilized as a foundation for continuous data collection and a cross-cutting organization surveys on rescue operation processes.

Seismic isolation retrofitting was conducted for Tsutenkaku tower of Osaka in 2015. The seismic isolation devices were installed at a height of about 9.5m above the ground. In this study, microtremor measurement and earthquake observation were carried out to investigate the earthquake response characteristic before and after the seismic isolation retrofit. The 2013 Awaji Earthquake and the 2018 Osaka North Earthquake were observed at both the basement and the roof floor. Simulation analyses of these earthquakes were made to discuss responses by the effect of seismic isolation retrofit.

During the 2016 Kumamoto earthquake, the extensive surface fault ruptures appeared along the active faults with a length of about 34 km and a maximum slip of about 2 m, resulting in various types of damage to buildings due to the strong ground motion and the fault displacement. The authors conducted a total of 6 field surveys in 2 years regarding building damage around the area within about 100 m from the fault ruptures, and investigated also the subsequent removal status. The appearance locations of the surface fault ruptures are generally consistent with those of the existing active fault map, but they deviate usually on the building scale of several meters. Except for the South Aso area, even though the fault displacement immediately above the fault rupture caused serious building damage, there was little major damage due to strong ground motion, and thus, the JMA Intensity scale was estimated to be 6 or less. On the other hand, the JMA intensity was estimated to be 7 in the South Aso area, because of the severe damage caused by strong ground motion; more than 70% of the collapsed and inclined buildings correspond to the direction perpendicular to the fault strike, suggesting the possibility of the forward directivity pulses. In all areas, severe damage was concentrated on old buildings with poor seismic resistance, whereas new buildings, especially those after the 2000 seismic building code were slight damage or undamaged, even right above the fault ruptures. In the subsequent follow-up survey, we confirmed that the more severe the damage grade was, the higher the rate of demolition was. However, we also confirmed that many buildings had been demolished with less than the moderate structural damage. Part of the reason seems to be due to the government policy that favors demolition over repair in the events of disastrous earthquake damage.