Section 4: Case Studies
The shear-wave velocity profile of a near-surface soil and/or rock site is one of the most important parameters for geotechnical estimation of earthquake shaking response at the ground surface. Downhole and surface seismic methods for measuring shear-wave velocities and mapping subsurface impedance boundaries include seismic cone penetrometer, downhole shear-wave vertical seismic profiling, surface-geophone array sites using refraction and reflection methods including array-to-source reversals, multichannel analysis of surface waves, seismic-reflection profiling, and horizontal-to-vertical spectral analyses of ambient noise. A suite of seismic shear-wave measurement methods has been tested in two Canadian cities with relatively high seismic hazard. Regional maps of National Earthquake Hazard Reductions Program (NEHRP) seismic site classifications (following the National Building Code of Canada) and fundamental site periods were created with the data. These maps indicate that broadband amplification effects and fundamental resonance periods can be extremely variable over short lateral distances within both survey areas. Such information needs to be considered by land-use planners and engineers working in such areas. Shear-wave velocity techniques constitute the most versatile approaches to earthquake-hazard mapping and site investigations.