CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Adams, J.
Date : 2004.
Title : A review of NBCC 2005 Seismic Hazard Results for Canada - the interface to the ground and prognosis for urban risk mitigation.
Publication : Geo-Engineering for the Society and its Environment. 57th Canadian Geotechnical Conference and the 5th joint CGS-IAH Conference. Hilton Quebec Hotel, Old Quebec. October 24-27, 2004.
Issue :
Page(s) :
Abstract
Earthquakes Canada’s new national hazard model will form the basis for seismic design in the 2005 edition of the National Building Code of Canada (NBCC). The model comprises two complete earthquake source models to represent the uncertainty in where (and why) earthquakes will happen in the future together with a deterministic model for a Cascadia subduction earthquake and a “stable craton” model that provides floor design values for the low seismicity parts of Canada. A “robust” method is used to combine the results: the mapped value is the largest of the values determined from the four sources. The building code will be based on median values of 5% damped spectral acceleration at periods of 0.2, 0.5, 1.0 and 2.0 seconds, calculated for firm ground at a probability of non-exceedence of 2% in 50 years (0.000404 per annum). New soil classes will convert the “firm ground” values to other foundation conditions. These factors depend on the strength of the shaking (to account for non-linear behavior of soils under strong shaking) and act to reduce design ground motions on rock and increase them on soft soils. For very soft or liquefiable soils a site-specific analysis is required. NBCC values provide a useful way to allocate earthquake protection across the nation and can be used as a first-order estimate of seismic risk (taking seismic risk to be proportional to “likelihood of damaging ground motion * population at risk”). Such an analysis ranks the cities as:- Vancouver, Montreal, Ottawa-Gatineau, Victoria, Toronto, Quebec City, etc, and provides a basis for allocating mitigation efforts. Improved strong motion monitoring of the cities at risk (articulated in a proposal called CUSP, Canadian Urban Seismology Proposal) could place up to 1000 internet linked real-time strong motion accelerographs across Canada, with their distribution reflecting the national urban risk. Direct monitoring of urban shaking at this level of detail will allow estimation of the likely damage, possibly within a handful of minutes after a large earthquake, thus enabling more effective emergency response efforts. CUSP is underway as a pilot project of 60 stations on a 1-km grid in greater Vancouver. While we wait for strong earthquakes, these instruments will provide ground motion records on a variety of soil sites and hence direct measurements of soil amplification. These will provide ground truth for other microzoning efforts such as those using ambient noise which can provide a more finely-detailed picture of ground conditions on a block-by-block basis. Such studies are underway in Montreal, Vancouver and Victoria, and in turn these efforts will feed back into the more effective deployment of any future accelerographs. The combination of CUSP-style monitoring together with more detailed microzonation should lead to better and safer cities for the future.
Bibliography of Canadian Geomorphology