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Earthquake Background Information
As many of you are aware, a magnitude 6.6 earthquake occurred at 7:30 a.m. PST near the southern tip of Queen Charlotte Islands region. The earthquake was felt across the Queen Charlottes/Haida Gwaii and throughout the North Coast. Our Emergency Coordination Centre even received a call from Prince George. Almost immediately, the Provincial Emergency Program began to receive calls from people wanting to know if there would be a tsunami, and reporting school closures and beach evacuations. This event is a reminder to us that we must be prepared for an earthquake, and how to react appropriately should one occur. Your local or agency emergency program is your key source of information for all things emergency management, but I hope this information is of use to you in your planning and response – I would like to ensure that people are making the best decisions with the most accurate information available.
The Queen Charlotte Fault
From northern Vancouver Island to the Queen Charlotte Islands, the oceanic Pacific plate is sliding to the northwest at about 6 cm/year relative to North America. The boundary between these two plates is the Queen Charlotte fault. Canada's largest recorded earthquake - a magnitude 8.1 - occurred along this fault on August 22, 1949. Due to the length of the Queen Charlotte fault, this is likely the largest earthquake the fault could generate.
The Queen Charlotte fault is a transform fault, meaning that the movement of the plates is horizontal. Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it reaches a level that exceeds the strain threshold of rocks on either side of the fault, the accumulated potential energy is released as strain. The energy released by instantaneous strain release is the cause of earthquakes, a common phenomenon along transform boundaries such as the Queen Charlotte fault.
A tsunami is a series of ocean waves caused by a rapid, large-scale disturbance of the sea water. Tsunamis can be caused by submarine volcanic eruptions, submarine landslides, and major earthquakes occurring beneath the seabed causing large vertical movements. Transform faults, such as the Queen Charlotte fault, have horizontal movement, not large vertical movement. The Queen Charlotte fault is not tsunamigenic, meaning it does not generate tsunamis. However, should a submarine landslide occur due to an earthquake along this fault, there is a potential for localized tsunami activity.
What to do if you feel an earthquake
If you are indoors: "DROP, COVER, and HOLD":
- Stay inside.
- Drop under heavy furniture such as a table, desk, bed or any solid furniture.
- Cover your head and torso to prevent being hit by falling objects.
- Hold onto the object that you are under so that you remain covered.
- If you can't get under something strong, or if you are in a hallway, flatten yourself or crouch against an interior wall.
- Stay away from windows, and shelves with heavy objects.
- If you are in a wheelchair, lock the wheels and protect the back of your head and neck.
If you are outdoors:
- Stay outside.
- Go to an open area away from buildings.
- If you are in a crowded public place, take cover where you won't be trampled.
If you are in a vehicle:
- Pull over to a safe place where you are not blocking the road. Keep roads clear for rescue and emergency vehicles.
- Avoid bridges, overpasses, underpasses, buildings or anything that could collapse.
- Stop the car and stay inside.
- Listen to your car radio for instructions from emergency officials.
- Do not attempt to get out of your car if downed power lines are across it. Wait to be rescued.
- If you are on a bus, stay in your seat until the bus stops. Take cover in a protected place. If you can't take cover, sit in a crouched position and protect your head from falling debris.
AVOID the following in an earthquake:
- Doorways. Doors may slam shut and cause injuries.
- Windows, bookcases, tall furniture and light fixtures. You could be hurt by shattered glass or heavy objects.
- Elevators. If you are in an elevator during an earthquake, hit the button for every floor and get out as soon as you can.
- Downed power lines – stay at least 10 metres away to avoid injury.
- Coastline. Earthquakes can trigger large ocean waves called tsunamis.
If you live near or are by the ocean
Early warning signs of a tsunami:
- The occurrence of avery large earthquake thatlasts for more than one minute, where the shaking is so severe that you cannot stand up.
- Rapid and unexpected recession of water levels below the expected low tide.
A tsunami may occur with very little warning.
What to do when a tsunami hits:
- Do not go near the shore to watch a tsunami hit. If you can see it, you are too close to escape.
- Should a tsunami occur and you cannot get to higher ground, stay inside where you are protected from the water. It's best to be on the landward side of the house, away from windows.
- Often tsunamis occur in multiple waves that can occur minutes apart, but also as much as one hour apart.
- Monitor the tsunami's progress andlisten for warnings or instructions from local officials. If you are safe when the first tsunami hits, stay put until authorities declare all is safe.
After a tsunami hits, you may encounter flood waters. Flood waters can be dangerous to walk or drive through. Before driving anywhere, it is best to listen carefully to rescue officials who will be coordinating evacuation plans.
Provincial Emergency Notification System (PENS)
When the Provincial Emergency Program receives an earthquake notification, emergency management staff in the Emergency Coordination Centre, together with technical and scientific staff from the Canadian Hydrographic Service in the Federal Department of Fisheries and Oceans, and/or the earthquake seismologists at the Pacific Geosciences Centre in Natural Resources Canada, assess the information to determine if BC coastal areas may be threatened. If there is a threat, this information is sent out to local government emergency officials through the provincial emergency notification system (PENS). The notification system speeds initial information to the places it needs to be: at the local authority level, and as well to the news media who can in turn get information out quickly to the public. The PENS is not initiated if no tsunami threat exists.
PENS is a very useful tool in the event of a distant earthquake generating a tsunami, but we do not expect that in the event of a locally occurring earthquake that we will have sufficient time to use PENS to warn people of a tsunami. Because of this, the earthquake itself has to serve as the tsunami warning, and severity is the most reliable indicator – the earthquake must last for more than one minute where the shaking is severe that you cannot stand up. If the shaking is not that severe, the chances of a tsunami occurring are very slim. Unfortunately, there is no way to provide any warning for submarine landslide generated tsunamis – they may occur in smaller earthquakes or even without an earthquake, and are localized to the site of the landslide. Your emergency program must, in the event of a submarine landslide generated tsunami, be prepared to deal with the impacts as opposed to the event itself.
There is a wealth of resources available on the web to assist you in planning for and responding to an earthquake and/or tsunami. Here is a sampling of just a few of the sites: