Monday, June 22, 2015

Ground Amplification Map, Victoria

Seismic amplification map, Victoria, BC, Canada
Red and orange are high and very high hazard
See Monohan and others (2000) for more detail

The seismic amplification map above is a simplified version of a much more detailed map that can be seen by clicking the link above. The higher hazard areas are subject to higher seismic risk because of the types of soil and how those soils may react to long wave period seismic events. Areas underlain by soft soils will respond differently to seismic events and are locations more likely to be damaged particularly from seismic waves that have a long period wave length. Hence, a quake some distance away with long seismic waves may cause extensive damage in the red and orange zones with no damage in the gray areas.

The gray areas on the map (grey if your Canadian?) are hard compact geologic units or bedrock and will be much less susceptible to damage from seismic events. However, a sharp high g force quake in close proximity will impact all areas of Victoria and the difference will not be as noticeable.

There are lots of other caveats with maps like this. Locations where waves get refracted or develop resonance (like a kid sliding back in forth in a bath tub) require knowing a lot about the underlying units and geologic basins and the predicted wave length of the seismic waves.

The short answer is being on bedrock or other very compact geologic unit is preferable and perhaps a consideration in planning where to build critical facilities.  

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