DATA COLLECTION FOR EARTHQUAKE HAZARD MAPPING IN THE OTTAWA AREA J.A. Hunter Geological Survey of Canada, Ottawa, Ontario, Canada, jhunter@nrcan.gc.ca D. Motazedian & K. Kaheshi-Banab Department of Earth Sciences – Carleton University, Ottawa, Ontario, Canada G.R. Brooks, M. Lamontagne, H. Crow, T. Cartwright, A. Pugin, M. Pyne Geological Survey of Canada, Ottawa, Ontario, Canada RÉSUMÉ Les provisions sismiques du Code de Construction National du Canada 2005 mentionnent la possibilité que d’importants tremblements de terre peuvent avoir lieu dans la région d’Ottawa. Une étude démonstrative de l’Université de Carleton et de la Commission Géologique du Canada est en cours pour mesurer les propriétés de l’onde cisaillante des unités géologiques dans la région d’Ottawa, Ontario. Le but de ce travail est d’améliorer notre connaissance des propriétés de l’onde cisaillante des sols meubles dans la vallée d’Ottawa pour une meilleure estimation et pour cartographier les amplifications sismiques et les effets de résonnances. Les résultats préliminaires indiquent qu’il existe d’importants contrastes de vitesse de l’onde cisaillante entre les unités glaciaires et postglaciaires ainsi que des variations locales majeures d’épaisseur des sédiments. En accordance avec les profondeurs variables, la prédiction et la cartographie de période fondamentale et des pics de résonance des sites démontrent également une grande variabilité. L’observation du bruit sismique ambiant local et d’événements télé-sismiques de tremblements de terre a confirme le faible mouvement estimé de la réponse du sol. Dans l’ensemble on peut prédire qu’un important tremblement de terre à Ottawa pourrait générer des intensités variables selon l’endroit en raison des épaisseurs variables et des propriétés géotechniques des sédiments glaciaires et postglaciaires qui reposent sur le fond rocheux de la région. La finalisation de la cartographie des paramètres de l’amplification sismique et de la période de réponse pour la région d’Ottawa est prévue pour 2009. ABSTRACT The seismic provisions of the National Building Code of Canada 2005 reflect the possibility that significant earthquake shaking can occur in the Ottawa area. A joint demonstration study by Carleton University and the Geological Survey of Canada is currently underway to measure the shear wave properties of geological units in the Ottawa area, Ontario. This work is designed to improve our knowledge of the properties of soft soils in the Ottawa Valley region in order to better estimate and map earthquake amplification and resonance effects. Results to date indicate that there are large shear wave velocity contrasts between glacial and postglacial surficial geological units as well as major local variation in unit thicknesses. Prediction and mapping of fundamental site periods and associated resonant peak amplitudes also reveal large variability, reflecting these same factors. Monitoring of ambient seismic noise of both local and teleseismic earthquake events has confirmed the estimated weak motion ground response. Overall, it is expected that a significant earthquake in the Ottawa area will generate variable shaking intensities spatially because of differing thicknesses and geotechnical properties of the glacial and post-glacial sediments that overlie the bedrock of the region. Mapping of earthquake amplification parameters and site period response for the Ottawa area is planned for completion in 2009. 1. INTRODUCTION The shaking experienced at a given site during an earthquake can be amplified significantly depending on the local geological-geotechnical properties of the underlying soil. The 2005 National Building Code of Canada (NBCC 2005) introduced descriptions of site categories that take into account the thickness and stiffness of a soil and provide estimates of the relative amount of amplification from seismic shaking. These site categories can be mapped using three-dimensional geological and geophysical data to produce seismic hazard microzonation maps that depict the spatial distribution of earthquake amplification hazards. Such maps have application towards, for example, allowing municipalities to enhance their emergency response planning, improve earthquake mitigation strategies, and develop urban growth plans that avoid amplification susceptible terrain. The Geological Survey of Canada (GSC) is currently mapping the NBCC site categories within the City of Ottawa, Ontario, to produce seismic hazard microzonation maps. This mapping represents a research activity of the ‘Eastern Canada Geohazards Assessment Project’ within the Natural Resources Canada ‘Reducing Risk from Natural Hazards Program’. The intent of this project is to produce science- based hazard assessment products for eastern Canada that have a direct application for the reduction of risk from earthquakes and landslides. This current paper provides an overview of the type of work being conducted in this project, along with some preliminary results to date. In : J. Locat, D. Perret, D. Turmel, D. Demers et S. Leroueil, (2008). Comptes rendus de la 4e Conférence canadienne sur les géorisques: des causes à la gestion. Proceedings of the 4th Canadian Conference on Geohazards : From Causes to Management. Presse de l’Université Laval, Québec, 594 p.