Identification of Topographic Seismic Site Periods in Sloping Terrains

The fundamental period of a terrain is a key parameter for characterizing the maximum soil amplification. Since the 1960s, research has been conducted for sloping terrains with a focus on evaluating topographic effects. However, few studies have focused on identifying whether the site topography induces an amplification peak that is associated with a characteristic period of sloping terrain. This study conducts a parametric analysis to identify a potential amplification pattern attributable to terrain geometry, using two-dimensional finite element models subjected to the action of a dynamic signal. The periods in which amplification peaks are generated are evaluated and compared with the amplification response recorded in the free field on horizontal terrain. The results reveal that the dynamic response of sloping terrain is a combination of the response from the surrounding terrain to the sloping zone and vice versa, and a distinctive amplification peak linked to the topography is identified. A new expression is proposed to define a topographic seismic site period in terms of shear wave velocity and the total soil thickness from the bedrock to the crest of sloping terrain. This study advances the processes of characterizing the seismic response of sloping terrains by demonstrating that the topographic seismic site period is consistent regardless of the slope angle. This provides engineers with a new dimension of analysis for the practical definition of criteria to determine topographic effects in design spectra.