Calculation of free field response spectrum of a non-homogeneous soil deposit from bed rock response spectrum

Abstract In this paper, a method to determine free field response spectrum of a soil deposit from a specified bed rock response spectrum is presented. This method treats the earthquake motion as if it was a stationary Gaussian random process but to account for the non-stationary character, an approximate method is used. The soil deposit is assumed to have mechanical properties (strength, shear modulus, etc.) increasing with some power exponent of depth. This layer overlies either a compliant elastic half space or a layer with shear modulus increasing linearly with depth. To demonstrate the validity and usefulness of this approach, two examples are presented. The first one consists in the transfer, from bed rock to free surface of a given soil profile, of the response spectrum derived from an accelerogram used to generate the Eurocode 8 response spectrum. The obtained free field response spectrum is compared to the one obtained by using a wave propagation program. The second example consists in the validation of this method with experimental records.