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TitleEarthquake hazard maps of the city of Ottawa, Canada, using near-surface geophysical and geological methods
AuthorHunter, J A; Crow, H; Brooks, G R; Pugin, A J M; Pullan, S E; Motazedian, D; Kaheshi-Banab, K
Source23rd Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010 (SAGEEP 2010); 2010 p. 418-427
Alt SeriesEarth Sciences Sector, Contribution Series 20100033
PublisherCurran Associates, Inc.
MeetingSAGEEP'2010 (Symposium on the Application of Geophysics to Environmental and Engineering Problems); Keystone, CO; US; April 6-10, 2010
Lat/Long WENS -76.4167 -75.2500 45.5333 44.9500
Subjectsgeophysics; soils science; earthquake studies; earthquake risk; earthquake catalogues; earthquakes; boreholes; tills; building codes; s waves; soils
Illustrationsgeophysical sketch maps
ProgramEastern Canada Geohazards Assessment Project, Public Safety Geoscience
AbstractThe city of Ottawa, Ontario, Canada is in an area of elevated earthquake shaking hazard and is considered to be the third most Canadian city at risk to damage (after Vancouver and Montreal). Maps showing regional variation of Vs30, fundamental site period, and an example map of the spectral accelerations at Sa=0.2s have been completed for the city at a reconnaissance scale. These have been developed from combined geological information from ~21,000 boreholes (water wells and geotechnical borings) within the city limits as well as ~700 surface and borehole shear wave seismic measurement sites. Borehole and surface shear wave measurement techniques developed for the operational area included: surface reversed refraction and reflection sites, MASW, downhole shear wave and horizontal-to-vertical spectral analyses of ambient noise. The surficial geology was subdivided into three basic units based on their geotechnical properties: soft fine-grained marine post-glacial sediments, glacial till and coarse-grained till-derived sediments, and firm Paleozoic and PreCambrian bedrock. A series of shear wave velocity-depth functions were assigned to each borehole location based on interpolation from proximal geophysical sites. The resulting three-dimensional shear wave velocity database was then used to determine parameters such as Vs30 and fundamental site period. The Vs30 map of the city is subdivided in terms of the U.S. National Earthquake Hazard Reduction Program (NEHRP) zones which have been adopted by the 2005 National Building Code of Canada. Since the City of Ottawa has a large areal extent and is close to the West Quebec Seismic zone, the base accelerations for the 2% in 50 year earthquake event vary extensively within the city boundaries. Hence an example map of the spectral accelerations at Sa=0.2s has been developed to demonstrate regional variations and the effects of NEHRP zones.