Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Local geological and geotechnical conditions can have significant effects on the incoming seismic waves and their spatial variation. Commonly referred to as site-effects, certain conditions can significantly amplify the intensity of the seismic shaking and make it more destructive. Site effects are accounted for in national building codes by the selection of amplification factors as functions of soil category, seismic intensity and frequency. The soil type is categorized by considering representative shearwave velocity, the number of blows in the standard penetration test, and/or undrained shear strength in the top 30 meters. Although soil categorizations based on these geotechnical parameters are more or less similar across earthquake-prone countries, there are some differences, which may result in over- or underestimation of the potential site effects. The SaguenayLac-Saint-Jean region (SLSJ) is located in a moderate seismicity zone in Eastern Canada; the last major earthquake in this region occurred in 1988 with a moment magnitude of 5.9. The presence of important deposits of sensitive clays in SLSJ combined with the strong impedance contrast between the unconsolidated deposits and the underlying crystalline bedrock can play an important role in the soil dynamic response. Different soil classification criteria and respective amplification factors are compared: the 2015 National Earthquake Hazards Reduction Program (NEHRP), Eurocode 8, and the 2015 National Building Code of Canada (NBCC). The advantages and disadvantages of each classification approach are discussed.