Abstract
Based on recent studies suggesting that Rayleigh waves are observable in microtremor ground motions, an improved procedure is proposed to estimate a natural period of a site using amplitude ratios between horizontal and vertical motions of the mictrotremors. The procedure is to make the best use of not only peaks but also troughs in a spectral amplitude ratio. Using microtremor data measured at all junior high schools in 23 wards of Tokyo, the proposed procedure is applied to a period-mapping of the area and compared with an existing map to a satisfactory level of accuracy, demonstrating its practicality.
