Amplitication of earthquake motion by surface soft deposits

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Soil amplification of earthquake motion was investigated. It has been known that the existing technique of earthquake response analysis on soft alluvium underestimates the surface motion. Since this is against the empirical knowledge that the damage is more intense upon the soft alluvium, study was needed to understand the cause of the discrepancy. Centrifuge tests were run to obtain the stress-strain behavior of sand undergoing shaking which was compared with the behavior obtained by conventional element tests without shaking. Field investigation by using micro-tremor technique was conducted in Kushiro City to compare the nature of ground with and without seismic damages during the earthquake in 1993. Finally, One proposes to consider the shear stiffness and damping ratio to vary with the frequency. The other takes the vertically-continuous variation of soil properties into account and solves the equation of wave propagation. Both can give a greater response upon alluvium that conventional types of analysis.