Dependence of sediment-filled valley response on input amplitude and valley properties

Abstract

Abstract For three sediment-filled valleys, average site responses were experimentally determined and found to apply, to within ±0.25 log units, to earthquakes at any azimuth and to S waves and coda waves; for one of these valleys, ground accelerations were measured over the range 10−5 to 0.2 g, and no significant differences in site responses were apparent. In two valleys with sediment-basement impedance contrasts of 5:1 and 6:1, average site amplification is as much as a factor of five in certain frequency bands. In another valley, with a sediment-basement impedance contrast of 3:1, sediment amplification is about a factor of two. The duration of motion on the valley sediments, in narrow frequency bands, is equal to that on the bordering rock, implying that the observed amplification is not due to a high-Q resonance of the sediments.