SASW measurement for the calculation of site amplification

Technical Abstract

Calculations of the site amplification effects of soft sediments were made at two locations in the Wellington region, Parkway in Wainuiomata and Wi-neera Drive in Porirua. At each location the soil shearwave velocity profile was measured using the Spectral Analysis of Surface Waves method (SASW). The shearwave velocities were combined with geotechnical data to formulate a soil model for each site which was used as an input to the computer program SHAKE, which calculates the seismic response spectrum for each soil layer.

The ratio of the response spectrum at the rock to the response spectrum at the surface provides a measure of the site amplification. This spectral ratio, determined using the SASW data, was compared with spectral ratios for the same locations determined using earthquakes records from the soft soil sites and from the closest rock sites.