Refinement and application of an estimation procedure for site natural periods using microtremor

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 motion of the microtremors. 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.