SEISMIC WAVE PROPAGATION IN ELASTIC SOIL WITH CONTINUOUS VARIATION OF SHEAR MODULUS IN THE VERTICAL DIRECTION

A conventional type of earthquake response analysis of ground gave a maximum acceleration for soft deposits that is lower than that for stiffer soil conditions. Since this was contradictory against the knowledge that soft deposits are more hazardous, an improvement of the analysis was attempted. A series of geophysical surveys was carried out to investigate the variation of shear wave velocity in the vertical direction and it was suggested that the velocity and shear modulus vary more continuously with depth even though the soil type changes from cohesive to cohesionless. The idea of continuity in soil property was further supported by the variation of fines content with depth. With these in mind, a wave propagation equation was developed and then solved analytically by taking into account the continuity of modulus. The calculated amplification of seismic motion indicated that more wave energy can reach the ground surface with this new analysis than in the more conventional way of calculation.