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TitleDevelopment of Vs30 and fundamental site period maps for seismic hazard estimation in Ottawa, ON
AuthorCrow, HORCID logo; Hunter, J A; Pugin, A; Brooks, G RORCID logo; Pyne, M; Motazedian, D
Source 2009, 9 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20090081
Meeting2009 Canadian Geotechnical Conference; Halifax, NS; CA
Lat/Long WENS-76.0000 -75.5000 45.5000 45.2500
Subjectsgeophysics; engineering geology; seismicity; seismic risk; seismic interpretations; earthquakes; earthquake risk; earthquake magnitudes; seismic velocities; velocity surveys; seismic surveys; reflection studies; seismic reflection surveys; refraction studies; seismic refraction surveys
Illustrationslocation maps; tables; profiles
ProgramReducing Risk from Natural Hazards
Released2009 01 01
AbstractIn spring of 2009, the Geological Survey of Canada, in partnership with Carleton University, released microzonation maps of the City of Ottawa that depict the distribution of 2005 NBCC seismic site categories (A through E) and fundamental site periods across the city. The maps were compiled using subsurface geology derived from 28,000 boreholes, and shear wave velocity (Vs) data from 685 reflection/refraction sites, 25 kilometres of shallow seismic landstreamer data, and nine downhole Vs logs. The seismic site categories map has a borehole database at its core, and was compiled by applying Vs-depth functions derived from shear wave reflection surveys to post-glacial deposits, and Vs ranges for glacial deposits and bedrock. These relationships allow for each borehole record to be converted into a shear-wave velocity profile, whereby the travel-time-averaged Vs for the upper 30 m of the ground surface (Vs30) could be determined for each borehole site. Seismic reflection/refraction data supplemented the map in areas of low borehole coverage and landstreamer profiles created high resolution seismic cross-sections in areas of complex bedrock topography. Fundamental site periods were calculated using the 2005 NBCC equation of 4*h/ Vs, where h is the depth to 'firm ground', or the primary impedance contrast in the stratigraphic sequence, and Vs is the average shear wave velocity at this depth. To produce the map products, GIS techniques were applied to the spatial interpretation of the complex dataset. Targeted end users of the map are the geotechnical engineering community and municipal officials for emergency preparedness and land use planning purposes.

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