On October 19, 2023, practice how to Drop, Cover, and Hold On at 10:19 a.m. during the annual Great BC ShakeOut.
The Great BC ShakeOut is an annual province-wide earthquake drill for everyone to practice how to protect themselves and to be better prepared in the event of an earthquake: Drop to the ground (before the earthquake drops you!), take Cover by getting under a sturdy desk or table, and Hold On to it until the shaking stops.
Why is this information important?
- Earthquakes can strike suddenly and without warning, so knowing what to do during and after an earthquake is very critical to ensure safety.
- You can secure items in your household to have reduced property damage.
- During an emergency, if the community is prepared, it helps first responders focus their effort on people who require immediate support and leads to efficient resource allocation.
For more information and to participate in the ShakeOut drill, please access the ready.ubc.ca ‘Are you prepared’ website.
Why do Earthquakes happen and could one happen here?
The Vancouver campus is located near where the Juan de Fuca Plate is moving westwards and is subducting (sinking) under the North American Plate. This happens just west of Vancouver Island and the two plates here are coming together and create a zone of compression near surface.
The movement between the plates is accommodated by a mix of sliding that we do not feel, and earthquakes that we do.
Earthquakes happen when friction between the two plates prevents sliding for a while, which allows tension to build up until the fault zone “pops” and moves all at once. Imagine pushing down on a book placed on the surface of a table, then trying to slide it.
The pushing together increases the friction between the book and the table, and so you can build up more tension before the system slides. Vancouver experiences lots of small earthquakes all the time, but could one day experience a very damaging earthquake in the range of magnitude 6 to 8 on the Richter Scale.
In the Okanagan, we are further from the edge of the North American plate, but we do live very close to a fault that runs up the middle of Okanagan Lake. Here, the North American plate is slowly stretching out as the area gradually readjusts from the formation of the Rockies, which was from 80-55 million years ago. There are two things that make our region different.
First, there is less plate movement to accommodate than near Vancouver.
Second, the two sides of the Okanagan fault are trying to move away from each other. To return to the book on the table analogy, imagine instead that you lifting the book and supporting some of its weight before you try to slide it sideways. In this case, you would build up far less sideways tension before the book slides.
These two factors mean we tend to get smaller earthquakes, the majority of which are never even felt. The largest in this region was a magnitude 4.5 in 2002 located about 50 km west of Kelowna, and all the rest are in the 3’s and below.
The logarithmic nature of the earthquake amplitude and energy scales means an increase of 1 in the Richter Scale is an energy difference of about 30. This means a magnitude 4 is a thousand times less powerful than a 6, about 30,000 times less powerful than a 7 and nearly a million times less powerful than a magnitude 8.
While the Earth sometimes surprises us, the Okanagan is not expected to encounter the same earthquakes as the Lower Mainland.
Dr. Craig Nichol, Assistant Professor, Earth & Environmental Sciences and Physical Geography