Assessing Seismic Response of Soft Soil Sites in Hong Kong Using icrotremor Records

Abstract

Microtremor records have been used to assess seismic ampiification of sou sites in Hong Kong. The method is based on ratios of horizontal and vertical camponents of microtremor (ambient noise) recards, and the ratios are aften referred to as Nakamura’s ratios. The peakfrequency of the Nakamura’s ratio carrelates well with thefundamental modal frequency estimated from the site shear wave velocities which were derived by a vertical seismic profiling method or were converted from SPT data. The amplitudes of the ratios are very stable and the standard deviation of the ratios derived from a series of measurements is reasonably small. Results from rock sites show that the ratios take a value of unity at a wide frequency range when the site has no large topographical effect. The ratios are generally larger than unity if the site has topographical effect but no dominant peak appears in the ratios. Results from sou sites show that a dominant peak appears at the fundamental frequency of the site and the amplitudes ...