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Earthquake Hazard Mapping (Vancouver Island)

Earthquakes have been an ever-present threat to the communities on Vancouver Island and the coastal mainland. AXYS, in conjunction with the Geological Surveys Branch and Monahan Petroleum Consulting, has produced a popular map series displaying areas susceptible to high hazards in the Greater Victoria area.

This map series displays different hazard ratings for the different forms of earthquake dangers, such as amplification, ground liquefaction and areas most likely susceptible to slope instability. Danger ratings are based on quaternary geology interpreted from ground sampling sites throughout the city. Hazard ratings can vary widely based on location.

These maps can be used for a variety of purposes. They can be a resource for planners, aide in emergency response routing and informing the public about general earthquake hazards near areas in which they live and work.

Earthquakes have always been a popular topic on Vancouver Island, and AXYS is proud to be a contributing member in the production of this important source of spatial knowledge.

Available Maps

To view the earthquake hazard maps online, or download you own set of maps in Adobe Acrobat format, visit the Ministry of Energy, Mines and Petroleum Resources web site.

Composite Relative Earthquake Hazard Map of Greater Victoria

The objective of this map is to show areas of Greater Victoria where the earthquake hazard is likely to be increased due to the presence of potentially unstable slopes, and soils susceptible to amplification of ground motion and/or liquefaction. This map has been compiled from three other maps: a relative liquefaction hazard
map, a relative amplification of ground motion hazard map, and an earthquake-induced slope instability hazard map.

Relative Amplification of Ground Motion Hazard Map of Greater Victoria

This map shows areas where the earthquake hazard is increased due to amplification of ground motion. The amplification of ground motion hazard has been estimated on the basis of the National Earthquake Hazard Reduction Program (NEHRP) site classes for the susceptibility to amplification of ground motion (Building Seismic Safety Council, 1994), which are based on the average response of various types of soils.

Relative Liquefaction Hazard Map of Greater Victoria

This map shows areas of Greater Victoria in which the earthquake hazard is potentially increased due to the presence of soils susceptible to liquefaction. Liquefaction is the transformation that occurs when earthquake shaking (or other disturbance) causes a saturated granular soil to lose its strength and behave like a liquid and can be one of the major causes of damage during an earthquake. The susceptibility of a site to liquefaction depends on the depth to water table and the density, grain size and age of the underlying deposits. This map was prepared by assigning a hazard rating to each geological map unit based on these criteria and quantitative analyses.

Seismic Slope Stability Map of Greater Victoria

Seismic slope hazard mapping is intended to show relative susceptibility to earthquake induced slope failures. The seismic slope hazard map is based on a compilation of existing subsurface data, previous slope stability assessments, bedrock geology and surficial geology maps, topographic data, and airphoto interpretation. Stability analyses were conducted on twelve different slope models including typical or simplified slopes found throughout the Victoria area as well as specific, complex slope models where more detailed information was available. The stability analyses determined both the static factor of safety and the yield acceleration (the intensity of seismic motions that would cause a slope failure).

Quaternary Geological Map of Greater Victoria

This map shows the thickness and distribution of the Quaternary stratigraphic units in Greater Victoria. It is intended to provide the geological basis for the assessment of the earthquake hazards shown on companion maps which depict the liquefaction and amplification of ground motion in Greater Victoria (Geoscience Maps 2000-3a and 2000-3b; Monahan et al., 2000b and c). The geological units shown here are defined in part to reflect these hazards.