Abstract
Short-period microtremors are observed at two sites using arrays. It is found that their variation with frequency of amplitude ratio between horizontal and vertical motions is stable during a 24-hour period and is similar to that of Rayleigh waves, and that the frequencies at which the amplitude ratio becomes the maximum correspond to the natural periods of the sites. The frequency wavenumber spectrum analysis of microtremor vertical motions yields Rayleigh wave dispersion curves which reflect the shear structures of the sites. These findings suggest that site effects can be reliably estimated by extracting Rayleigh wave characteristics from microtremors.
