The Georgia Basin, an elongated bowl-shaped depression in south western British Columbia, has been studied recently to help seismologists gain a better picture of earthquake threats in the area. An article posted by CBC discusses how the shape and relatively soft make up of sedimentary rock around Vancouver can cause the area to experience earthquake shaking for longer than the surrounding areas.
The Georgia Basin is shaped like an elongated bowl and lies beneath the Georgia Strait, between the Lower Mainland and Vancouver Island. It is one in a series of basins along the Pacific coast of North America, and is filled with layers of silt, sand and glacial deposits.
‘We’re bringing the earthquake up through the cheese, and then it’s suddenly hitting the Jell-O mould and starting to slosh around and bounce around within that Jell-O.’– Sheri Molnar, UBC Civil Engineering, describes seismic waves in the Georgia Basin
She compares the Georgia Basin to gelatin surrounded by a hard block of cheese.
“We’re bringing the earthquake up through the cheese, and then it’s suddenly hitting the Jell-O mould and starting to slosh around and bounce around within that Jell-O.”
British Columbia sits on what’s known as the Cascadia subduction zone, where earthquakes tend to occur either within the Juan de Fuca plate or the overriding North America plate. Big subduction earthquakes, like the one that struck Japan in 2011, also occur in the Juan de Fuca plate.
Molnar’s studies examined the potential impact of deep earthquakes, with a magnitude of 6.8, that occur 40 to 50 kilometres beneath the surface, as well as shallow earthquakes of the same magnitude.
This is, of course, interesting from a geological perspective, but geographically speaking it raises concerns for the construction of appropriate buildings and other infrastructure in municipalities of the Georgia Basin. New construction projects will have to be put in place with a mind towards accommodating for a greater level of potential damage from prolonged seismic events. Older buildings may require additional upgrading to ensure they are up to code and able to withstand the effects of these earthquakes. Ultimately, the concern here is with financial resources available to make these changes and the environmental impact of doing so.