A method for accurately estimating the dynamic characteristics of buildings shaken by microtremors of the ground and partly governed by wind forces was investigated. Displacements and wind velocities at an 18-story building were observed for about one year. Dynamic characteristics of the building estimated from microtremors were found to be affected by wind forces at the first resonance frequency of the building. It was also found that transfer functions of the roof to the basement generate overlylarge apparent damping factors under conditions of strong winds, but power spectra of the roof produce apparent damping factors whose accuracy are scarcely affected by wind velocity. A simulation model and a highly simplified wave propagation model for the building and soil were studied and they offered an explanation for the results described above.
