In this paper, modal analysis has been carried out to study lateral force distribution caused by the difference between stiffness and the weight to hybrid structure of upper wooden story and lower RC story, and the level of plastification and damages are discussed by referring to inelastic time history analysis.
We conducted a damage survey of wooden structures and collected very dense ambient noise measurements in the near-source region of 2011 Northern Nagano earthquake. The percentage of totally collapsed buildings exceeded 30% in Aokura and Yokokura districts in Sakae village, Nagano prefecture. The percentage in Mori district, where strong motion was recorded during the mainshock, was less than 10%. We estimated the strong motion in the Aokura and Mori districts from the ambient noise measurements and strong motion records. The estimated strong motion distribution reflects the soil conditions, and varies in that small area. The correlation of estimated strong motion and damage ratio of wooden structures is reasonably high, which indicates the estimated ground motions are realistic. The damage curve obtained from this research shows the collapse ratio exceeds 50% around 150 cm/s of input ground motion.
A model fault is supposed and strong ground motions are predicted around the fault by stochastic Green's function method to compare indexes such as PGA, PGV and energy index named IED(Incident Energy Density). It is necessary to show the validity of the predicted motions but the indexes such as PGA and PGV should not be enough to represent the characteristics of earthquake ground motions. In this study, we study the applicability of IED of a seismic wave to estimate validity of the predicted strong ground motion. IED of a predicted strong ground motion has good relation to magnitude of earthquake. The variation of IED due to the phase characteristics of element seismic waves used in stochastic Green's function method or the difference of soil characteristics is less than PGA and PGV. It can be concluded that if IED is added to evaluation indexes, it is possible to estimate more rationally the validity of a predicted strong ground motion.
We propose empirical correction methods for an existing ground motion prediction equation of inland crustal earthquakes at rock sites in combination with numerical simulation of ground motion amplification and analysis of observed records, which introduces a correction term considering sediment amplification effects. Proposed methods utilize either sediment depth or average S-wave velocity of deep subsurface structure as an explanatory variable. Empirical prediction method of these explanatory variables from dispersion curve of Rayleigh wave phase velocity is also proposed.
One of the problems in the application of the stochastic Green's function method (SGFM) is that the Fourier spectrum of the synthetic ground motion shows a fall-off in a middle frequency range. For the purpose of solving this problem, I examine the method to apply the fault model that considered heterogeneity of the distribution of the rise time and the final slip based on the rectangular crack model. The approximate expressions of the rise time and the final slip are shown for application to the estimation of strong ground motion. The fault model based on the approximate expressions is applied to the sample of the strong ground motion estimation using SGFM. Using this fault model, compared with the case that the uniform fault model is used, the Fourier spectrum of the synthetic ground motion by SGFM does not show an evident fall-off.