Validation of small strain properties from recorded weak seismic motions

Abstract

During the last decade, there has been an increased interest in the computations of surface ground motions from known rock outcrop motions. The main advantage of the procedure is to allow for the actual variation of strength and stiffness properties of heterogeneous soil profiles, eventually accounting for non-linear soil behavior. The main questions raised against the adequacy of such a procedure lie upon the reliability of the computational scheme and in the representativity of the soil constitutive relationship. The present paper addresses both aspects by comparing the motions computed assuming standard assumptions in the state of practice of earthquake engineering. Since until now, the downhole array recorded only weak motions (horizontal peak ground accelerations smaller than 0·04 g), the paper focuses on elastic soil properties. It is demonstrated that a carefully conducted geotechnical survey yields an accurate shear wave velocity profile and that rate-independent soil damping might not be appropriate to represent the soil behavior in the small strain range.