The 2000 Tottori-ken Seibu earthquake caused severe damages in Tottori and Shimane Prefectures. The KiK-net Hino observation site, operated by the National Research Institute for Earth Science and Disaster Prevention, is situated near the seismic fault. The vertical array records observed at the site provide valuable information about wave propagation at large strain level. In this study, temporal changes of propagation times of seismic waves were examined based on Normalized Input-Output Minimization (NIOM) analysis. These examinations revealed that (1) the S-wave propagation time increased from 0.197 s to about 0.35 s due to nonlinear behavior of soils; (2) gradual decrease of the propagation time of S wave was observed a thousand days after the mainshock, however, the propagation time was still larger than the value before the mainshock; and (3) the P-wave propagation time also increased due to the principal motions during the mainshock. Subsurface soil properties were also examined based on the above results and pointed out that (4) an abrupt decrease of shear rigidity to 20 MPa at strain of 3×10^-3 during the principal motion of the mainshock, and gradual increase up to 100 MPa after the mainshock were observed, whereas (5) the Poisson ratio was about 0.46 to 0.47 and almost independent of strain level.

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Empirical equation of liquefaction strength curve, which is applicable in wide range of number of cycles causing liquefaction, is proposed for effective stress analysis. Past similar researches have several disadvantages from the practical point of view; soil classification is not considered and applicable range is limited to small number of cycles or uncertain. In our research, test results of undisturbed samples with variety of soil classification and with number of cycles causing liquefaction larger than 100 are collected. About 200 test results are classified from several points of view. It is found that both geological age and fine fraction content are important factors. Considering the use of practical engineering, equations predicting R_L5 and R_L100 from R_L20 is proposed based on geological age (Bs+As or Ds). Finally, a smooth equation is proposed for liquefaction strength curve which covers number of cycles causing liquefaction between 5 and 100.

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This paper presents an evaluation of amplification characteristics in subsurface structure with inclined bedrock based on inversion of autocorrelation functions of ground seismic motions that are easily observed. If a 1D structure is known and an autocorrelation function of a correct 2D model is a target, we perform a grid search for an inclined angle and a damping factor with 2D-FEM analysis. Amplification characteristics of the optimized model show good agreement with the correct answer at a virtual site. Then, we apply the evaluation method to actual sites and confirm its effect. Autocorrelation functions of observed records correspond with those of 1D model in a horizontally layered site and with those of 2D model in an inclined bedrock site.

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A horizontal orbit of observation in near fault area shows elliptical shape. First of all, we estimated response of base isolation system by a multiple shear spring model for one-directional and bi-directional input motions. We found that the response from bi-directional input show larger amplitude than those from one- directional input in some cases, indicating the importance of the particle orbit characteristics of strong ground motions. Next, we theoretically calculated strong ground motions in near fault area using the wavenumber integration method. As a fault becomes shallow, a horizontal orbit changes from linear shape to ellipsoidal shape. Moreover, we estimated the contribution of near-field term to the change by Green function of elastic fullspace and investigated the effect on two-dimensional response of base isolation system.

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This study focuses on S-wave velocity structures in Yangon City, Myanmar, where the seismic safety of constructions is insufficient while strong ground shaking due to earthquakes nearby are expected in the near future. In this study, we investigated underground structures based on the horizontal-to-vertical spectral ratios (HVRs) of single-station microtremors as well as phase velocity estimated by array measurement of microtremors inside Yangon City, which can be used to simulate strong ground motions during future crustal earthquakes or used as information for microzonation studies. Microtremor explorations were conducted at 27 sites including one array site at the ground of University of Yangon. The observed results showed the consistent HVR peaks for the fundamental mode in the lower frequencies ranging from 0.7 to 1.3 Hz, while they showed also the other peaks at higher frequencies ranging from 20 to 40 Hz. The final S-wave velocity structures showed that the topmost layer may have a thickness of 1 to 2m with the S-wave velocity of 140m/s and that the 5^th deepest layer exists at around 100m below the surface throughout the observed area, as the engineering bedrock with the S-wave velocity of 800m/s.

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The new improvement method that can reduce the liquefaction damage of the small structures by making the high permeable gravel layer near the ground surface is proposed. The proposed method makes the gravel layer under the outer circumference of the structure, and drainage to ground surface is provided. The effect of the proposed method is confirmed by centrifugal model tests. The proposed methods do not have the effect to prevent liquefaction, but it is possible to significantly reduce the inclination of the structure caused by liquefaction. It is most effective to carry out the measures in all directions of the outer circumference of the foundation. Applied the measures to a pair of opposing sides of the foundation is also large effective for reducing liquefaction damage.

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This study is reasonable liquefaction prediction of Urayasu in case of the Great East Japan Earthquake based on RSPM. In the one-dimensional seismic response analysis use RSPM, the actual measurement and analysis value of maximum surface acceleration were congruous on the natural deposition ground. However, it was confirmed at the reclaimed land that maximum acceleration become small. In order to carry out reasonable liquefaction prediction in case of a trench type great earthquake, it was confirmed that it is necessary to take into consideration the regionality of a liquefaction strength ratio and the influence of a long-time continuation earthquake motion.

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During the 2011 Great East Japan Earthquake, houses, roads and lifelines suffered serious damege due to liquefaction at many excavated and replaced grounds in eastern Hirai district of Kamisu City. Main reasons of the damage were: i) differential ground settlement occurred at the edges of the excavated zones, and ii) penetration of houses into the ground. Then appropriate countermeasures to mitigate the damage during future earthquakes were studied by analyses and in-situ tests. As a result, the method of lowering the water table was selected. The applicability of the method to this district was studied by in-situ drainage tests.

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In this study, it is found that the attenuation characteristics of strong ground motion from megathrust subduction earthquakes will be very different when using different distance measurement. When using fault distance, it is found that the strong ground motion will stop to increase with moment magnitude for earthquakes with M_w larger than 8.3 (it is called magnitude saturation); when using equivalent hypocentral distance, however, such saturation becomes to be not significant. In comparing the fault distance and the equivalent hypocentral distance for M_w 9 and M_w 8 class earthquake, it is found that the equivalent hypocentral distance for M_w 9 class earthquake can be about 6 times larger than the fault distance, while for M_w 8 class earthquake the difference is only about 1.7 times in near field area. It is found that such differences cannot be canceled for M_w 9 class earthquake by applying the conventional distance saturation term, unlike the M_w 8 class earthquake. However, the difference may be cancelled by considering the magnitude saturation. The results also show that the equivalent hypocentral distance for M_w 9 class megathrust earthquake may vary largely with different slip model.

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In the current assessment method of liquefaction based on F_L, reduction factor of the seismic shear stress ratio r_d is given as a function only for depth from ground surface. However, it is known that the seismic shear stress is dependent on the earthquake motion characteristic and non-linear site response characteristics. In this study, the method of evaluating the reduction factor r_d of seismic shear stress is newly proposed from strong motion record. The tendency of the seismic shear stress which occurs in the actual ground can be reflected on the assessment method of liquefaction by applying the proposed method to a large amount of strong motion record.

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Large span structures such as a gymnasium and an exhibition hall often use ceilings because of enhancing sound effects and reducing heating bills. The ceiling member fell down on a large scale due to the seismic motion according to the past great earthquake disaster reports. The purpose of this study is to investigate the vibration characteristics and propose the response performance evaluation method of the steel base conventional method ceiling in the school gymnasium based on the microtremor measurement and the time history analyses. The validity of the proposed practical method has been shown in comparison with the analyses.

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We examine three research topics to infer reliable Green's functions (Gfs) of vibration of torsionally coupled buildings. The first is waveform deformation of Gfs associated with rotation due to the lack of low-frequency content in incident rotational motions. To correct it, we propose two methods: an addition of band-cut-filtered uncorrelated noises to the incident rotational motions and weighting zero-lag autocorrelation of the incident rotational motions. A comparison of Gfs corrected by the two methods revels that the addition of the noises is better than the weighting. The second is the effect of wind on building vibration. A temporal fluctuation of building vibration is much more similar to that of incident microtremors than a temporal fluctuation of wind. Furthermore, Gfs inferred from microtremor vibration acquired during a time span of low-level wind blow and high-level incident microtremors are almost same as those inferred from microtremor vibration acquired during a time span of the reverse. These results mean that wind does not affect the Gfs under condition that a mean wind velocity is less than 2m/s, and incident microtremors are more than 0.002 m/s². The third is data-length to infer reliable Gfs. Non-dimensional averages of root mean square error of Gfs inferred from 3- hour-length data reduce to one third of that of Gfs inferred from half-hour-length data, which suggest that we use data-length above 3 hours to infer reliable Gfs. Practically, it is recommended to use microtremor recordings acquired in the nighttime from 23:00 to 5:00.

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The examples of damaged R/C building with walls in Tohoku Earthquake were collected. And, the standard prototype data of the frame with walls was proposed. In order to understand structural properties and damage states for non-structural R/C wall vertically located in a span with spandrel walls, the structural experimental test of three specimens, which variable parameters are different opening patterns, wall thicknesses and wall bar arrangements was conducted. The experimental result showed that the structural characteristics were highly-influenced by the presence of the spandrel wall, and allowable strength evaluated by the AIJ standard of R/C was on the safe side, and that initial stiffness was calculated rather highly, ultimate strength was calculated precisely in the skeleton curve.

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This study investigates vertical response of seismically isolated building focusing on the differences of span length of superstructure. We investigate several base-fixed moment-resisting frame models with the equivalently added damping to incorporate the SSI effect. There is no difference between frame models and lumped mass models, when span length is short. On the other hand, the effect of beam vibration is large, when span length is long. Axial force of isolator is largely affected by beam vibration of superstructure. We tested equivalently added damping only to columns, setting the original damping to beams with distributed masses. Coupling effects of vertical responses with SSI can be adequately evaluated in comparison with added damping to beams and columns constantly.

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The loading tests of traditional wooden joints with wedges were carried out by use of Teflon sheets which reduce the friction in order to make clear the effects of wedges on the restoring force characteristics. The results showed that the effects of wedges on the restoring force characteristics were very large and the resisting mechanisms of joints with wedges were established. Thus, based on their mechanisms, formulations of restoring force characteristics of joints with wedges were proposed and some simulations were tried.

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Many coastal protection facilities were damaged by the 2011 Off the Pacific Coast of Tohoku Earthquake and the subsequent tsunami, which spread inundation to the coastal plain area. Countermeasures of compound disaster by future mega earthquake such us, Nankai trough earthquake having high probability etc., are issues that should be resolved urgently. The resilient structures that can reduce damage when they are subjected to earthquake and tsunami higher than the design earthquake and tsunami are being developed. The authors developed a resilient reinforcement technique of breakwater foundation using gabion mound (mound covered with gabion) and steel sheet pile that can minimize damage when the tsunami is higher than the design tsunami height. In this research, model tests and elements tests were performed to evaluate the seismic resistant behavior of the proposed reinforcement technique. To that end, the authors performed triaxial tests for the rubble used as mound material in the model test to evaluate shear deformation properties during static and dynamic loading. The authors then performed shaking table model tests in 1G gravitational field to evaluate the effect of steel sheet pile installation and gabion reinforcement. Results of this research show that the mound material can mobilize excellent shear resistance under both static and seismic loading condition. Furthermore, the results also made it clear that the settlement and deformation of the breakwater during earthquake could be restricted by reinforcing the foundation using steel sheet piles and gabion.

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Strong motion records during the 2011 off the Pacific coast of Tohoku earthquake were obtained at high-rise RC buildings in the Tokyo metropolitan area. This paper presents the evaluation of dynamic properties of a high-rise RC building based on 3-D frame analysis. From these studies, the following results were obtained. (1) Relationship between the relative displacement and temporal variation of the natural frequency based on 3-D analysis was consistent with the earthquake observation records. (2) The height-wise distribution of story drift angle was dependent on the levels of the input earthquake motion and showed different characteristics for the pulse type input motions. (3) For the larger input motion where the structural responses exceed far beyond the experienced responding levels, maximum response is not largely affected by whether it experienced seismic responses before or not.

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Recently, there have been some researches on analysis using finely-meshed FEM model to understand in detail the behaviors of buildings during severe earthquakes. The accuracy of such an analysis is often validated by comparing the analytical results with the corresponding full-scale shaking table test results. While they are highly successful in the accuracy, few take account of the sequence effect of multiple series of excitations, in the other words, the effect of inherent structural damage caused by prior excitations. In this paper, as a first step toward a design considering fore/aftershocks, numerical analysis using finely-meshed FEM model is conducted for a steel structure subjected to multiple series of excitations in a full-scale shaking table test. The FE model structure is modeled with planar and solid finite elements. It is shown that, by taking account of the history of input excitations and caused damages, the actual behaviors can be simulated by analysis with much higher accuracy.

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Large inelastic response can be developed in reinforced concrete columns with isolator due to the second stiffness of the isolator if columns yield. Effect of uncertainty in ground motion characteristics on the seismic damage allocation and failure mode of reinforced concrete columns with isolator was investigated using incremental dynamic analysis in this study. It was shown that failure mode of the reinforced concrete column with isolator depends on the characteristics of ground motions.

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In this study, we deal with a method for damage identification of composite girder bridges based on the changes in the modal characteristics. Generally damage to structure causes any change in modal characteristics of the structure. From the results of modal analyses of a girder bridge with sixty damage scenarios, it became clear that the changes in the primary mode shapes of target lines have a close relation to the places and degrees of damages to the bridge. We proposed a method for damage identification of girder bridges based on the changes in primary mode shape.

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It is effective to establish improvement priorities about the prevention methods for the labor accidents after earthquake. This paper presents development of evaluation models for probability of labor accidents occurring in disaster restoration works from partially damaged house by the earthquake using the relationship between the number of the accidents classed as "fall to lower level" in the building work and the number of partially damaged houses in disaster-affected areas.

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This paper discusses the transition of seismic risk on residential building damages using seismic hazard curves of National Seismic Hazard Maps for Japan. By calculating expectation values of residential building damages in 1890, 1920, 1950, 1980, 2010 and 2040 in Japan, we consider their changes and aspects. In order to calculate, we estimate distribution of residential buildings and loss functions in each base year. The result shows that the changes of seismic risk are influenced by subduction-zone earthquakes with specified seismic source faults and concludes that it is important to evaluate seismic risk with a view to temporal axis.

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This study performed a series of experiments on vehicular evacuation in case of tsunami using a driving simulator. The driving simulator was equipped with a tsunami inundation scenario, which assumes the occurrence of the 1498 Meio earthquake. 31 examinees were employed for the driving simulator experiments. In these experiments, we installed a function of route guidance to evacuation spot assuming a car navigation system. A tsunami hazard map was also displayed during driving to notice the expected tsunami inundation areas and depths to the examinees. The results of the experiments were evaluated to reveal the effective measures to transmit tsunami information to drivers. Based on the experimental results, displaying a hazard map is not sufficient to improve the evacuation rate. Various countermeasures, such as use of traffic signs, assigning priorities of vehicular evacuation in the city, and disaster prevention education, are required to enhance a safety evacuation in case of tsunami.

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About 4,200 places of cracks and steps at the road surface were confirmed at the embankment of the expressway by Tohoku district Pacific coast earthquake to be generated on March 11, 2011. In addition, the damage a trouble has caused in traffic in a main line was 21, and these were extensive damage relatively. We analyzed collapsed factor of embankment of 3 places. The topography by which an embankment collapses in an earthquake in the past was the ravine where foundation inclined and soft ground. Further, such as excess pore water pressure inside the embankment in the flat ground became expensive because of this earthquake, an embankment of the condition that surface moistures are collected collapsed. This paper, we assumed clearly that it collapsed big when agreeing with the fixed condition by an analysis of the factor by which an embankment at the flat ground collapsed. Furthermore, the method of construction of earthquake-proof measures effective and practical to an embankment of the similar condition was proposed.

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Buildings and residential houses were severely damaged due to the ground motion at the downtown area of the Namie town, Fukushima prefecture during the 2011 off the Pacific coast of Tohoku Earthquake. Damages survey revealed that the damage ratio was not uniform even in the downtown area. In order to clarify the reason, we observed ground motions during aftershock events and microtremors in the downtown area of Namie town. The H/V spectral ratio obtained from single station observations imply that the peak frequencies uniformly distribute in the downtown area. S-wave velocity models obtained from array observations indicate low velocity in surface soil layer. Observed ground motions during the aftershocks also imply that the difference of ground motion amplification due to shallow soil layer is not significant within the downtown area.

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Serious damage including ground liquefaction occurred at Fusa District, Abiko City during the 2011 off the Pacific coast of Tohoku Earthquake (2011/03/11 14:46 M_W9.0). The site was also affected by the 2011 off Ibaraki Prefecture Earthquake (2011/03/11 15:15 M_J7.6) and the 2011 Hamadori, Fukushima Prefecture, Earthquake (2011/04/11 17:16 M_J7.0). Evaluation of strong ground motions during the past 3 earthquakes at this site with sufficient accuracy is very important to clarify the ground disaster mechanism. In this study, seismic waveforms at this site were estimated based on the site-effect substitution method. The estimated seismic waveforms will be useful in the detailed study of the mechanism of observed ground disaster.

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After the 2011 Tohoku earthquake, the shallow earthquakes increased in off Ibaraki and Fukushima prefecture area, Japan. We examined the long-period strong ground motion in the Tokyo bay area from those events with hypocenter depth shallower than 60 km and magnitude over 6.5 in Japan Meteorological Agency scale. The duration of the velocity waveform of shallower event was longer than that from deeper event and the amplitude of the long-period ground motion of shallower event was larger than that of deeper event. The later arrivals with period of 3-10 second affected these phenomena. There was the case that source mechanism affected on the excitation of long-period strong ground motion. Consideration of source depth and source mechanism is necessary to evaluation of the long-period ground motion in the Tokyo Bay area. In addition, the site amplification of body waves was also observed in long-period range. It is important to evaluate the site effect of deep sub-surface structure.

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In the conventional design method, there is no particular method to judge the liquefaction phenomenon of the unusual soil such as volcanic ash soil. This study, in order to clarify and evaluate the liquefaction characteristics of volcanic ash soil, field investigations and a series of soil laboratory tests of volcanic ash ground were carried out. The field investigations and sampling were conducted in the areas where ground liquefaction occurred due to the 1993 Hokkaido-nansei-oki and the 2013 Tokachi-oki earthquakes. According to the results, the liquefaction ratio (R_L) was underestimated when using the formulation of the conventional design method. Moreover, it was found that the estimated formulation R_L need to be modified for evaluating the liquefaction phenomenon in volcanic ash soil.

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