ANALYTICAL AND NUMERICAL INVESTIGATION OF THE SITE RESPONSE PERIOD IN THE SAGUENAY REGION, EASTERN CANADA

Soils' local geological and geotechnical properties may lead to sharp variations of seismic shaking and structural damage at small distances. These so-called seismic site effects significantly impact the amplitude and frequency components of the ground motion. Key site effect parameters are the shear wave velocity of soils (Vs), indicating the material stiffness, and the fundamental vibration period (To), a function of Vs and thickness of the soil units (H) given approximately as To=4H/Vs. This quarter wavelength method often underestimates To values as the nonlinear soil behavior during earthquakes, where stiffness degradation increases the site period, is not accounted for. The present study applies the multi-layered method by Hadjian (2001) and empirical correlations developed with the single-layer approach to calculate To. The Saguenay Lac-Saint-Jean region (SLSJ) was selected as the study area. It is characterized by moderate seismic activity and complex Quaternary stratigraphy, including stiff glacial sediments, and soft Laflamme Sea deposits with recent alluvial plains on top, exhibiting a strong impedance contrast with the underlying crystalline bedrock. Numerical analyses also examined the effects of the soil nonlinearity on To establishing their correlation for different hazard levels according to NBCC 2020 guidelines.