GEOTECHNICAL SITE INVESTIGATION OF SUBSURFACES BY SURFACE WAVES CONSIDERING HIGHER MODES

The analysis of seismic affected areas and the evaluation of seismic risk of the developed areas demand the knowledge of the dynamic site characterisation. While doing so, the site dependent seismic excitation including the dominant site frequencies and the filtering and amplification effects are necessary to be determined. Beside the earthquake characteristics, the realistic soil parameters are also needed for the numerical site investigations. Undisturbed soil profiles can be efficiently assessed with the help of the surface wave propagation. By using inversion methods, the soil stiffness profiles can then be calculated. In such cases, mostly the measured fundamental mode of the surface wave is used without the consideration of higher modes of surface waves. However for describing the complete surface wave propagation, all the excited modes are necessary. In this paper, the appeared higher modes of the surface waves were detected by using various multi-trace methods. Also, an inversion method was used that considers various higher modes. Some field measurement data were utilised to determine the dispersion characteristics using the inversion method. While considering the higher modes, the weighted excitation factors were used. In this way, the realistic soil shear wave profiles were obtained. The shear wave profiles can be utilised to calculate stiffness profiles