EARTHQUAKE SITE-RESPONSE STUDY IN GIUMRI (FORMERLY LENINAKAN), ARMENIA, USING AMBIENT NOISE OBSERVATIONS

We have tested whether ambient noise observations reveal useful inform ation regarding site response at sediment sites in Giumri (formerly Le ninakan), Armenia. This was done by comparing the noise observations w ith spectral-ratio site-response estimates based on aftershock data of the 7 December 1988 earthquake. We show that neither the horizontal-c omponent noise spectra alone, nor spectral ratios taken with respect t o a nearby bedrock site, reveal useful information regarding site resp onse. However, spectral ratios of horizontal components taken with res pect to vertical components (Nakamura's method) exhibit a prominent pe ak 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 deter mining the fundamental resonant frequency of sedimentary deposits from ambient noise observations.