Abstract
This paper indicates new microzonation maps of Perth, Western Australia, utilising microtremor spectral ratios. This metropolitan area has been developing in recent times on Perth Basin which is one of the most active seismic zones in the country. The authors carried out simultaneous measurings of microtremors over most of metropolitan Perth, using a 3 km grid as a basis and hard rock reference site throughout. They calculated spectral ratios of microtremors at deposit site to rock reference site and plotted and contoured on maps for 6 frequency bands from 0.2 to 5.0 Hz. Spectral ratio contours appeared to correlate well with various geological subsurface contours. They also showed that previously estimated earthquake risk estimates underestimated ground motions by up to a factor of two.
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