Microzone effects in the Hutt Valley in records from a strong-motion accelerograph array
Ground motions recorded in several earthquakes by the Hutt Valley strong-motion accelerograph array are analyzed to demonstrate and quantify microzone effects. Spectral amplifications in low to moderate ground shaking are calculated at sites with different soil conditions with respect to a reference site located on rock adjacent to the edge of the valley. It is shown that the response characteristics of various sites correlate well with the soil conditions underlying the sites. A shallow site located on 20 m of sediment adjacent to the edge of the valley produces short-period amplification, with the average amplification curve for the 5% damped acceleration response, spectrum peaking at 0.35 s with a value of 4. Deeper sites with up to 300 m of stiff sediments yield broad-band amplifications up to 2 s period, with typical maximum amplifications of 5-10. The greatest amplifications, exceeding 10, are obtained at two sites which are located on shallow very soft deposits.
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Copyright (c) 1992 S. Sritharan, G. H. McVerry
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