In this paper, we examine the dynamic properties of an existing three-story steel-framed house based on the observation records obtained from seismic observations and microtremor measurement. As a result, it was concluded as follows. The first is that a decrease in the natural frequency and an increase in the damping constant, which are thought to be caused by earthquakes and secular changes, were observed. The second is that even within an earthquake, the natural frequency drops during periods of particularly large amplitude and then recovers. It is possible that these phenomena mainly depend on reversible phenomena such as friction between non-structural members. The third is that at the microtremor level, the natural frequency is higher and the damping constant is smaller than during the earthquake.

It is important to appropriately set the nonlinearity of subgrade reaction characteristics in seismic calculations of buried pipes subject to ground deformation such as fault displacement etc. In the seismic design guidelines and standards related to buried pipes, the nonlinearity of subgrade reaction characteristics is based mainly on experimental data. On the other hand, in recent years, analysis technology has advanced and it has become possible to analyze elasto-plastic properties up to large deformation regions. Therefore, this paper reports the results of analyzing the mechanical features based on the results of two-dimensional elasto-plastic analysis that reproduces the results of subgrade reaction force experiments of buried pipes. Based on the results of FEM analysis, we consider a simple method for approximating the subgrade reaction force of yielding condition using Rankine's plasticizing stress and the comparing result is shown.

A detailed vibration experiment of a vehicle was conducted to understand the behavior of automobiles to seismic ground motion within wide range of the input level. As a result, followings were revealed: the dynamic characteristics of the vehicle changes with the input level, it is almost flat at 1 to 2 Hz, and the intensity index of the ground motion such as the instrumental seismic intensity can be estimated using the acceleration recorded on the vehicle. In conclusion, feasibility of the seismic observation using the automobiles was suggested.

A probabilistic tsunami risk assessment is conducted using the data from “Probabilistic Tsunami Hazard Assessment for Earthquakes Occurring along the Nankai Trough” published by NIED (National Research Institute for Earth Science and Disaster Resilience). To identify areas where tsunami countermeasures should be prioritized, we assess the probability that present coastal facilities (levees) can protect against inundation damage (non-exceedance probability) in the event of the next Nankai Trough earthquake. Based on this evaluation of the present levees, Uwajima City, Ehime Prefecture, is selected as the target area, and probabilistic inundation hazard maps are then produced for the existing levees and raised levees conditions (3.5 m for all areas where the levees are less than 3.5 m in height). Furthermore, the amount of damage reduced by raising levees is calculated based on the method of Fujima and Hiwatari (2013), and a cost-benefit analysis is carried out. As a result, the cost-benefit ratio is estimated to be 1.22, confirming the effectiveness of the levee raising project. It is expected that the inundation risk assessment method proposed in this study will be utilized by local governments to promote tsunami countermeasures for the next Nankai Trough earthquake.

Site-specific ground motion prediction using insufficient number of observed data at each site is a challenge issue. This paper proposes a framework to construct a site-specific ground motion model using the multi-output Gaussian process technique that makes it possible to predict site-specific ground motion in case of insufficient number of observed records at each site by utilizing the information obtained from records at other sites. In this paper, first, a proposed framework is validated using simulated records of hypothetical crustal earthquakes. The estimation accuracy is estimated depending on the number of sites and the number of observed records at each site. When earthquake locations are uniformly distributed and their magnitudes follow the Gutenberg-Richter relation, it is confirmed that the characteristics of site-specific ground motions can be accurately predicted over any distance range, provided there are at least nine stations and each station has at least 50 observed records. Then, the framework is applied to observed records to discuss the characteristics of site-specific ground motion. The results suggest that site-specific seismic motion predictions could be made using multi-output Gaussian process regression. In the ranges with ample records, the estimated uncertainty varied from site to site, with a logarithmic standard deviation between 0.2 and 0.4. The results also indicate an increase in uncertainty at close distances, which corresponds to statistical errors due to insufficient records.

The propagation time of the seismic waves from the bottom of the slab foundation to GL−40 m was estimated using Normalized Input-Output Minimization (NIOM) analysis for earthquake records obtained from seismic observations on the slab foundation of the buildings and in the supporting Layer (GL−40 m) at the Toyosu campus of the Shibaura Institute of Technology. The results showed that the observed propagation time varied, but this variation was related to the distance between the plane waves passing through the upper and lower seismographs, assuming that the seismic waves were plane waves. The propagation time evaluated from the borehole data showed relatively good agreement with the average of the observed propagation time, indicating that the averaging process may be able to eliminate some of the above-mentioned variation. Next, we applied the NIOM analysis to the observation records of the 2011 Great East Japan Earthquake to examine the nonlinear characteristics of the ground. The results indicated that the maximum shear strain in the ground was about 5 to 6 × 10^-4 and that the shear stiffness ratio G/G₀ may have decreased to about 0.8 to 0.6.

The Earthquake Research Committee (ERC), the Headquarters for Earthquake Research Promotion in Japan creates and updates national seismic hazard maps based on seismic intensity to help developing effective measures against earthquake hazards. In other countries, seismic hazard maps based on response spectra have become widespread and are being used for engineering purposes such as seismic design. In light of this situation, the ERC considers map-based response spectra for engineering purposes. Recently, the ERC released a provisional probabilistic seismic hazard analysis (PSHA) of response spectra. The provisional PSHA focuses on 5% damped acceleration spectra on the engineering bedrock of Tokyo, Nagoya, and Osaka and calculates seismic hazard curves, uniform hazard spectra, and degrees of influence by earthquake category. We anticipate that the continued development of PSHA response spectra will contribute to the evaluation of structural seismic responses for different exceedance probabilities and the implementation of seismic designs. Based on the provisional PSHA, the ERC is working toward effectively communicating PSHA response spectra results in ways that meet the needs and expectations of users for effective implementation.

We carried out damage investigation around the seismic stations where high JMA seismic intensity scales were recorded in the 2021 off Fukushima Prefecture Earthquake. We found some minor damage such as damage to the roof tile, the outer wall and the glass, but heavily damaged buildings were not found around all the seismic stations. We investigated the correspondence of strong ground motions with damage to buildings. Short period below 1 s were dominated in most of the ground motions and the 1–1.5 s response which correlates with heavy damage to buildings. Therefore, heavily damaged buildings were not found in spite of high JMA seismic intensity scale.