This paper describes the amplitude-dependent dynamic characteristics of a nine-story building in Sendai before, during, and after the 2011 Tohoku earthquake. The dynamic hysteresis characteristics are investigated using actual observations. Findings on induced higher harmonics on the basis of wavelet analysis suggest partial uplifting in the transverse direction. These features are consistent with the damage. Using long-term monitoring data from micro to strong motions in the building (40 years since its completion), the historical changes in the dynamic characteristics are also explored.
This paper presents and analyzes the identified vibration characteristics of steel high-rise building built at Shinjuku. The vibration characteristics, i.e.; natural periods, damping coefficients and participation functions, are identified from the measured acceleration during some earthquakes including the mainshock of the 2011 off the Pacific coast of Tohoku Earthquake. The curve-fitting method using the transfer function is applied in the identification. The change in natural period before and after the earthquake and the dependency on the modal amplitude are clear. The damping coefficients for the 1st and 2nd modes are found to be unexpectedly smaller than 0.02, that has been conventionally assumed in design of steel buildings.
After the Great East Japan Earthquake, importance of tsunami evacuation is increasingly acknowledged. The authors conducted questionnaire surveys of residents' evacuation in Onjuku, Chiba, focusing on an estimated tsunami in 2008 and on the event. Then acquired evacuation spatial data are compared in terms of altitude, distance from the coastal line, and the number of people in the inundated area. As a result, the actual evacuation activities in comparison with the estimated showed (1) diversity, (2) numerous uses of cars, (3) longer distance, and (4) more people in the inundation area.
The Great East Japan Earthquake exerted serious damage over an unprecedentedly wide range. The earthquake prevented the supply of materials indispensable to restoration and revival in its aftermath, including fuels such as gasoline. In this study, we apply a system dynamics solution to investigate the causes and bottlenecks of this problem in order to ameliorate similar problems in wide-ranging disasters that are expected to occur, such as the Huge Nankai Trough Quake.
The modal properties of a three-story reinforced concrete building that was affected by the 2011 Tohoku Earthquake were revealed through acceleration records of the main shock and ambient vibration. Damaged stories were detected from identified natural modes from the records. In addition, we estimated the modal parameters using two types of frequency domain decomposition techniques: one for a general viscous damping system and the other for a proportional damping system. The influence of the viscous damping condition on the identified natural modes was discussed.
Modal parameters of a nine-story steel-reinforced concrete building damaged heavily by the 2011 off the Pacific coast of Tohoku Earthquake were identified from ambient vibration data using frequency domain decomposition (FDD). The characteristics of the identified three-dimensional mode shapes, torsional component of the mode and deformation ratio of the mode were discussed with respect to the seismic damages. In addition, we identified the mode shapes by two kinds of FDD: one for a general viscous damping system, and the other for a proportional damping system. The influence of a viscous damping condition on the identified mode shapes was discussed.
We have constructed a shallow underground structural model of Kochi City for an area 10.5 km east-west by 5.5 km south-north with a resolution of 125 m, which could control seismic amplification in the short period up to 1 s. By compiling the geological information given by the Committee of Kochi Geo-Hazard Evaluation (2011), we constructed a multilayered model overlying the engineering bedrock with an S-wave velocity of 700 m/s. Based on our newly developed model, the dispersion characteristics of theoretical surface waves at two sites were calculated and verified by comparison with observed data derived from our microtremor array experiments. The predominant periods along two north-south lines calculated from our model were coincident with previous observations derived from microtremor H/V spectral ratios by Mori et al. (2001). We also conducted a seismic response analysis using the synthesized ground motion data from the Central Disaster Management Council of Japan (2003) as the input motion applied to the basement of the developed subsurface structural model. We confirmed that the area where relatively high seismic intensity was predicted corresponded well with the area that was severely damaged during the 1946 Nankai Earthquake.
The 2011 Tohoku Earthquake which exceeds the maximum magnitude of historical earthquake records could not be predicted. Which means, in the probabilistic tsunami hazard assessment for the future prediction, it is necessary to apply a different concept from the existing scenario tsunami assessment based on the maximum magnitude of historical earthquake tsunami. As a new modeling method for scenario tsunami, we propose a characterized tsunami source model which indicates setting method of the area of tsunami source and slip distribution by the inter-plate earthquake.