Numerical estimation and HVSR measurements of characteristic site period of sloping terrains

The characteristic site period, T₀, is an essential parameter to estimate the impact of local site effects on ground motion as it is a very useful tool for defining the period of vibration at which greater signal amplification can be expected. For a sloping terrain, unlike what is seen with horizontal terrains or low gradients, the response to a seismic event requires at least a two-dimensional (2D) analysis to determine T₀. This study evaluated T₀in sloping terrains with an angle of inclination > 15°. The dynamic response of the terrain was evaluated using 2D and three-dimensional (3D) finite-element modelling. Following the recommendations for recording vibrations in a sloping terrain, different measurements were taken using the horizontal-to-vertical spectral ratio method. From the results obtained with the 2D and 3D models for terrains with different geometrical configurations along with field measurements, it was observed that any point on a sloping terrain experiences two amplification peaks, the maximum values of which are related to the same periods as any other point along the gradient of the terrain. Therefore, on a sloping terrain, it is more appropriate to associate two characteristic periods that depend on the characteristics of the surrounding soil.