A multidimensional site response analysis is conducted to evaluate the site amplification of ground motions in surface ground. The tools for this analysis have been well developed, and these analyses can be one of the options for seismic motion evaluation in structural design. In order to further promote this situation, a two-dimensional two-layer linear site response solver was constructed using a machine learning model. It is confirmed that the solver can be used to easily evaluate the ground amplification at the ground surface position for any two-dimensional two-layer soil structure. Also, by using the solvers, it may be possible to elucidate phenomena related to the site amplification, perform uncertainty analysis in reliability design, and perform inverse analysis of soil structures more efficiently.

It is known that seismic ground motion is locally amplified in irregularly layered ground such as valleys and cliffs. In the southern part of Kanto region, there are many Holocene valleys through terraces, called "Yatsu." In such areas, the risk of disasters during an earthquake will be high. In this study, seismic observations were conducted for three Holocene valleys in Chiba Prefecture. The records at the center part of valleys show different characteristics compared to those of other part of valleys depending on direction. In order to investigate those phenomena, two dimensional analyses of the three valleys were conducted. The models of 2D analysis were created based on the ground survey. The results of the analyses show good agreements with the seismic records. It is shown that the seismic ground motions at Holocene valleys were affected by the subsurface irregularly layered soil structures.

This paper describes the passive control method of tuned mass dampers (TMD) for reducing seismic response in reinforced concrete buildings. To reduce seismic response in a wide range of strong ground motion levels, the displacement-dependent optimal tuning ratios of linear TMDs in nonlinear response were formulated. Then, we proposed performance curve diagrams using the optimal tuning ratio through nonlinear time history analysis with various mass ratios and damping ratios. These diagrams allow us to visually determine the appropriate TMD under the constraints of TMD's mass, damping coefficient, and peak deformation. For mid-to-high rise buildings subjected to various ground motions, spatial frame analyses were conducted to demonstrate the engineering applications. The peak response showed good agreement with the estimations based on the performance curve diagram. Without excessive deformation, the TMD reduced the peak displacement of the buildings by 10 to 15 percent.

The strong ground motion of the 1923 Kanto earthquake was recorded at Hongo, Tokyo by a Ewing disk-recording strong-motion seismograph. The seismograph consists of SW-NE, SE-NW and U-D components, and the original seismogram was traced on a tracing paper by Nasu (1957). The traced seismogram shows four sets of the traces which are lines of discontinuity due to scale-out of the indicator of the seismograph. Considering the different arm length curvatures in traces of the three components, the three component traces are distinguished from four sets of the traces. Although the distinguished traces have blank parts due to the scale-out of the indicator from the disk, the peak amplitudes of the SW-NE and SE-NW components are estimated to be about 20 cm and 40 cm, respectively.

Long-term monitoring is carried out on the Toyosu campus of Shibaura Institute of Technology. Accelerometer sensors are installed at the buildings incorporating base isolation devices and in the ground. The microtremor records for nine years were analyzed by FFT. As a result, it is found that there is a negative correlation between temperature and the natural period of the buildings, and the periods have increased by about 5% since the 2011 off the Pacific coast of Tohoku earthquake. The earthquake records were analyzed using the ARX model. As a result, it is found that the natural period and damping ratio of buildings are dependent on the amplitude of vibration. The periods have increased by 6 to 10% due to the above-mentioned earthquake, but the damping ratios have not changed.

At 14:46 JST on March 11, 2011, an earthquake with a moment magnitude of 9.0 struck northern part of Honshu Island, Japan. This paper first presents the distribution of 271 sites where the damages were particularly severe in Shirakawa City and the surrounding area, Fukushima during the earthquake. They can be classified roughly into five categories according to the types of damage: landslide and natural slope failure, sliding and failure of earth structure and large-scale developed area by cutting and filling hills, ground deformation due to soil liquefaction in low-lying area, vibrational damage, and over-turning of gravestone and stone pagoda. Next, the land conditions of 14 areas where severe and widespread ground failure-induced damage are investigated. Finally, the geomorphological and geological characteristics of the damaged areas are summarized and problems in countermeasures against future earthquake disaster are discussed.