Damages of river dikes caused by liquefaction have been observed after earthquakes. In 1995 Hyogoken Nambu earthquake, it was reported that many river dikes were settled and deformed by the liquefaction. The river dike in the middle region of Shinano River is built on the loosely deposited sandy layers. Therefore a large settlement and deformation of the river dike by the liquefaction of the ground is expected. A large scale of damage was reported in this region by the previous earthquakes such as 1964 Niigata earthquake, 2004 Niigataken Chuetsu earthquake, and 2007 Niigataken Chuetsu-Oki earthquake. Furthermore, as many active faults exist in this region, a big earthquake is expected in near future. Therefore, it is very important to understand the deformation mechanism of the dike by liquefaction of the ground and to predict deformation and settlement of the dike after earthquakes.
 In this study, effective stress based finite element analyses are carried out by the program code "LIQCA" to reproduce the past damege and to predict the damage of the river dike. Three earthquake motions by the 1964 Niigata earthquake, the 2004 Niigataken Chuetsu earthquake and the 2007 Niigataken Chuetsu-Oki earthquake have different duration times and maximum accelerations. At first, an analysis was carried out to reproduce the post damages by the 2004 Niigataken Chuetsu earthquake. As the result, the settlement and deformation are in good agreement with the actual behavior after earthquake. Secondly, the comparisons among damages by three earthquakes were carried out using three different earthquake motions. The duration time and the maximum acceleration motion are the key factors which affect the damage of the river dike by different earthquake. As the result, it is confirmed that deformation of the river dike by liquefaction of the ground is not only influenced by maximum acceleration but by duration time of the earthquake motion.

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We investigated the method of developing classification and story building data from census population database in order to estimate earthquake damage more accurately especially in the urban area presuming that there are correlation between numbers of non-wooden or high-rise buildings and the population. We formulated equations of estimating numbers of wooden houses, low-to-mid-rise(1-9 story) and high-rise(over 10 story) non-wooden buildings in the 1km mesh from night and daytime population database based on the building data we investigated and collected in the selected 20 meshs in Kanto area. We could accurately estimate the numbers of three classified buildings by the formulated equations, but in some special cases, such as the apartment block mesh, the estimated values are quite different from actual values.

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The 2008 Iwate-Miyagi Nairiku earthquake caused severe damage in the southern part of Iwate and the northern part of Miyagi Prefectures. The KiK-net Ichinoseki-Nishi observation site, operated by the National Research Institute for Earth Science and Disaster Prevention, is situated near the epicenter. The vertical array records observed at the site provide valuable information about the wave propagation at a large strain level. In this study, the temporal changes of S-wave propagation time were examined based on the Normalized Input-Output Minimization (NIOM) analysis. The NIOM analyses were carried out for the vertical array records observed during the mainshock and the events before and after it. The results revealed that (1) the S-wave propagation time increased from 0.258 s to about 0.35 s due to nonlinear behavior of the soil; (2) this propagation time corresponds to the 60% reduction of the shear moduli of the surface layers (ground-64m depth) and the strain level of 1×10^-3; and (3) the propagation time after the mainshock was still larger than the observed propagation time before the mainshock, and gradual decrease of the propagation time was observed during six months after the mainshock.

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The damage survey data of railway structures in the 1978 Miyagi-ken Oki earthquake, the 1995 Hyogo-ken Nanbu earthquake, and the 2004 Niigata-ken Chuetsu earthquake are collected and compiled. The seismic vulnerability functions of railway structures for different geomorphologic conditions are constructed in the range of the JMA seismic intensity 4 to 7. The results indicate that the railway structure damage appears from the JMA seismic intensity 5+ and that the damage is higher at mountain, hill or valley plane.

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Seismic slope stability of a high-rise fill embankment was thoroughly investigated. The high-rise fill embankment was constructed on a ravine with mountain stream for the development of a housing lot thirty-five years ago. Since the fill embankment is located in the middle part of Japan, a seismically active area, possible failure during earthquake has been carefully examined through geotechnical surveys, field and laboratory tests, and calculations of vibration behavior and slope stability for two years. In this paper, we present the applicability of these survey and analysis methods to assess a failure risk of fill embankments as well as the results of the investigation and calculation conducted in this study.

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The structural health monitoring (SHM) is a key technology for visualizing structural health. In this paper, a prototype system for SHM aimed at practical application was proposed and developed. In order to implement a database system into the prototype, a database model for SHM was also proposed. As a key unit for the system, a smart sensor system that has automated data acquisition and communication with the server was developed. We verified good and stable performance of the SHM system. The prototype SHM system could continue functioning for 53 days. The system identification algorithm based on ARX modeling implemented into the SHM system could estimate the first natural frequency of wooden buildings and steel buildings successfully from free vibration as well as micro tremors. We expect the developed SHM system would be our platform for future SHM systems.

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