Two-dimensional basin-scale seismic site effects in the Kitimat Valley, British Columbia, Canada: a practical example of using a fast hybrid FE/ BE method

The two-dimensional (2-D) basin-scale seismic site response of the Kitimat valley, located in the North Coast region of British Columbia, Canada, was investigated. The valley was subjected to a synthetic ground motion corresponding to a realistic local crustal earthquake of moderate magnitude consistent with the prevailing seismic hazard in the Kitimat region. SiteQUAKE, a fast hybrid finite element (FE)/boundary element (BE) numerical code was used for analyses, in which linear and equivalent-linear soil behavior models were implemented. The near-field (the sedimentary basin infill) and far-field (surrounding bedrock) were modeled by the FE and BE methods, respectively. Responses at different locations along a cross-section were compared with the input motion to illustrate the importance of basin effects. By dissociating the peak ground responses affected by the sub-surface topography (basin emptied of its infill) and by the presence of the sediment infill, it was shown that one-dimensional (1-D) analyses can either underestimate or overestimate 2-D seismic responses, highlighting their inability and insufficiency to correctly address basin effects.