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We have tested whether ambient noise observations reveal useful information regarding site response at sediment sites in Giumri (formerly Leninakan), Armenia. This was done by comparing the noise observations with spectral-ratio site-response estimates based on aftershock data of the 7 December 1988 earthquake. We show that neither the horizontal-component noise spectra alone, nor spectral ratios taken with respect to a nearby bedrock site, reveal useful information regarding site response. However, spectral ratios of horizontal components taken with respect to vertical components (Nakamura's method) exhibit a prominent peak that corresponds to the fundamental resonant frequency observed in the aftershock data. Based on this and other recent investigations, we conclude that Nakamura's method may be a reliable procedure for determining the fundamental resonant frequency of sedimentary deposits from ambient noise observations.
Field et al. (Wed,) studied this question.