The sequence of earthquakes that started rumbling northwestern Alberta on Nov. 23 started out small. Most of the quakes detected about 40 kilometres southeast of Peace River over the next week were not even felt by locals. But then came an earthquake on Nov. 30 that most definitely was felt. Indeed, it was the largest recorded earthquake in Alberta history.
The 5.6-magnitude quake originated at least four kilometres underground. Reports of shaking were felt as far as away as Calgary, approximately 700 km from the epicentre.
To get a better understanding of what caused these earthquakes and when Alberta may feel some more, UToday sat down with Dr. Rebecca O. Salvage, PhD, postdoctoral associate in seismology in the Department of Geoscience:
How common are earthquakes in Alberta?
Natural earthquakes (those caused by tectonic forces) are relatively rare in Alberta, and the events that we do get are usually small to moderate in size, compared to other areas of the world. Those that do occur are probably related to movement on deep faults, which formed when Alberta was much more geologically active hundreds of thousands of years ago. However, we actually record many small earthquakes related to human activities (e.g., hydraulic fracturing, water disposal, resource development) here in Alberta, known as induced seismicity. Most events are too small to feel, but occasionally there will be an induced seismic event that is felt.
Are different areas of Alberta at higher risk of earthquakes than others?
The areas at greatest risk of induced earthquakes in Alberta are close to ongoing operations, so Peace River, Rocky Mountain House, Musreau Lake etc. Natural earthquakes are much less common, but do occur in several distinct areas including the Rocky Mountain Fold and Thrust belt and its foothills, the Peace River Arch, and Milk River. Stress related to the formation of the Rocky Mountains, somewhere between 85 and 55 million years ago, is still dissipating across B.C. and Alberta, which can cause faults to move and generate earthquakes.
Do we know what caused the most recent earthquake in Alberta?
Initial depth estimates put the mainshock between four and seven kilometres deep, which could suggest a natural origin. Typically, induced events occur shallower than this and occur in correlation with ongoing activities in both time and space. However, there are events such as the quake on Nov. 30, 2022, which muddy the water; it occurred at a depth that is right on the transition between induced and natural, and, although no operations were reported at the time of the event, there is some evidence to suggest that distant operations, in both time and space, can sometimes induce earthquakes.
UCalgary, in collaboration with provincial and national agencies, along with other academic partners, are investigating the sequence of events to better determine its causes and characteristics. At the moment, the jury is still out.
Are we seeing more quake activity in Alberta in recent years than we have historically?
There has been an apparent increase in the number of detected earthquakes in Alberta in recent years, but this comes down to two factors. First, we have an improved network of monitoring stations now, which means we are better able to detect smaller events which previously would have gone undetected. Second, we do have an increase in human-induced earthquakes in Alberta, compared to historical records, simply because we have many more resource-development activities here in the last decade. However, only about 0.8% of hydraulic fracturing operations result in felt events.
If we try and determine a background rate of natural earthquakes in Alberta, although difficult to establish because of several contributing factors, it does appear that there is no increase in event rate in recent years.
Is there anything Albertans should do to prepare for future earthquakes?
Albertans should know what to do if an earthquake occurs: drop, cover and hold on.
- Drop: As soon as shaking starts, drop to the floor. Do not try to move to another room, do not use the elevator as power may go out, and do not try to run outside, which is more dangerous due to falling debris.
- Cover: Cover your head and neck with hands and arms, and, if possible, get under some furniture like a table or desk. This will protect you from falling debris.
- Hold on: Hold on to your cover and wait for the shaking to stop.
- Once the shaking has stopped, count to 60 to allow the dust and fallen objects to settle. Then move with caution as items may be unstable, and be aware that aftershocks may occur and you will need to drop, cover and hold on again.
- Do not call 911 to report an earthquake. Only call 911 if you need medical assistance.
- If you are in a car, pull over, set the handbrake and stay inside the car until the shaking stops. Try to avoid stopping close to structures (e.g., bridges, overpasses) and avoid trees, powerlines etc., which may collapse.
Canada is getting its own earthquake early warning system in the coming years. Similar to an amber alert, a text message will be sent to mobile devices to warn of possible shaking. However, since the waves from an earthquake travel so quickly, the amount of time between getting an alert and feeling shaking is likely to only be a few seconds. To learn more on how to protect yourself during an earthquake, click here.
