Canada (CAN)

Authors:

J. Adams, S. Halchuk, T. Allen, G. Rogers

Summary

The Global Hazard Mosaic coverage of Canada uses Canada's 5th Generation Seismic Hazard Model (Halchuk et al., 2015), produced by Natural Resources Canada (NRC), in order to develp the 2015 National Building Code of Canada. The model was originally developed for GSCFRISK software, and was subsequently converted into the OpenQuake (OQ) engine format by NRC. Small, additional adjustments were made by the GEM Secretariat in order to fit the mosaic criteria.

Information about the OQ model versions and input files can be found on the Results and Dissemination page.

Interactive Viewer

The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.

viewer_legend

Tectonic overview

Canada is, overall, tectonically stable, though tectonic activity does exist at the western margin. Here, the Pacific plate translates northward relative to the North American plate. This relative plate motion is, for the most part, parallel to the plate margin and the Queen Charlotte Transform, the major plate-boundary fault. The Queen Charlotte Transform produces quite a bit of seismicity, but the earthquakes are dominantly strike-slip and quite a ways offshore of the sparsely-populated mainland. The northwestern and southwestern margins are a bit different, however. In the north, the plate margin bends to the west, which induces a large convergent component to the relative plate motion, and deformation includes both strike-slip and reverse faults that are distributed throughout the western Yukon Territory. In the south, subduction of the Juan De Fuca plate occurs off Vancouver Island in the northern reaches of the Cascadia Trench. Very recently, paleoseismic evidence of sparse upper-plate seismicity has been found in southern British Columbia (e.g., Morell et al., 2017, GSA Today).

Basic Datasets

Please refer to Halchuck et al. (2015) and Allen et al. (2015).

Hazard Model

Seismic Source Characterisation

The input model includes three OpenQuake source typologies:

  • seismicity modelled as area sources based on the historical distribution of earthquakes, regional seismotectonics, or a hybrid of these
  • onshore simple fault sources in northwestern Canada and Alaska
  • subduction thrusts and other faulting offshore Canada's west coast, modelled as complex and simple fault sources

The source model is subdivided geographically to represent each quadrant of Canada. The western two quadrants use a single area source model and both typologies of faults. In the northeastern quadrant, historical and regional area source models are weighted at 0.6 and 0.4, respectively. In the southeastern quadrant, historical, regional, and hybrid models are weighted at 0.4, 0.4, and 0.2.

Epistemic uncertainty of the model parameters (downdip extent of the Cascadian subduction zone, maximum magnitude, etc.) is accounted for by a complex logic tree (see Halchuck et al., 2015).

Ground Motion Characterisation

Active Shallow Fault Weight
WesternCan15RjbLow 0.2
WesternCan15RjbMid 0.5
WesternCan15RjbUpp 0.3
Subduction Interface Weight
SInterCan15Low 0.2
SInterCan15Mid 0.5
SInterCan15Upp 0.3
Active Shallow Crust Weight
WesternCan15Low 0.2
WesternCan15Mid 0.5
WesternCan15Upp 0.3
Subduction IntraSlab30 Weight
SSlabCan15Low 0.2
SSlabCan15Mid 0.5
SSlabCan15Upp 0.3
Subduction IntraSlab50 Weight
SInterCan15Low 0.2
SInterCan15Mid 0.5
SInterCan15Upp 0.3
Active Shallow Offshore Weight
OceanicCan15Low 0.2
OceanicCan15Mid 0.5
OceanicCan15Upp 0.3
Stable Shallow Crust Weight
EasternCan15Low 0.2
EasternCan15Mid 0.5
EasternCan15Upp 0.3

Results

Hazard curves were computed with the OQ engine on a grid of 138284 sites (spaced at approximately 10 km) with a rock reference site condition, corresponding to a shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s. The computation was performed for peak ground acceleration (PGA), and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s.

The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.

References

Allen, T. I., Adams, J., & Halchuk, S. (2015). The seismic hazard model for Canada: past, present and future. In Proceedings of the tenth pacific conference on earthquake engineering building an earthquake-resilient pacific, Sydney, Australia (Paper number 100) Google Scholar.

Halchuk, S., Allen, T. I., Adams, J., & Rogers, G. C. (2014). Fifth generation seismic hazard model input files as proposed to produce values for the 2015 National Building Code of Canada. Geological Survey of Canada, Open File, 7576.