The Value of Alternative Geophysical Methods in Determining Shear Wave Profiles for Critical Infrastructure

Abstract

The impact of earthquakes worldwide on critical infrastructure has shown the importance of accounting for site effects in safe design. Including comprehensive shear wave (Vs) profiles in ground motion prediction equations has become an increasingly popular method. Yet, borehole measurement of Vs velocities in the near surface remains expensive. For locations with a perceived low seismic risk and little previous Vs investigation, this cost becomes a barrier to further development. This study examines three alternative geophysical methods and their value to determining site response. The methods are carried out at a previously uncharacterised strong ground motion station in the UK. The results of the testing were consistent within 10% of each other, producing a Vs30 of 570ms ± 30ms for the site. Moreover the methods give indications of the variability of the site, a lower limit of the resonant frequency and clear validation of the geological profile. Thus, if correctly applied, these methods can provide a viable and cost-effective alternative to purely invasive techniques.