The 7.9-magnitude earthquake that struck off the coast of Alaska early Tuesday morning did trigger a small tsunami but one expert says it could have been so much worse.
“It is really difficult to figure out how big a tsunami is going to be until it starts coming onshore or until we start getting wave measurements,” says geophysicist Mika McKinnon.
“A tsunami, we can predict how soon it is going to arrive very, very well. We’ve got the arrival times down perfectly.”
“That’s why the alerts and warnings lasted so long because there are not that many places between Alaska and Tofino where we actually do those measurements. We had to wait until the tsunami started arriving before we could figure out how big it is going to be.”
Turns out this one was very small — less than a foot high.
The U.S. Geological Survey says the quake struck at about 1:32 a.m. PT and had a preliminary reading of 8.2, which it later revised to 7.9. It struck 278 kilometres southeast of Kodiak at a depth of about 10 kilometres.
Residents along B.C.’s coast were woken by warning sirens shortly after the quake struck off the coast of Alaska.
A dozen aftershocks followed the earthquake — the biggest being a 5.6 magnitude.
McKinnon says this earthquake was originally thought to be a subduction zone earthquake, which happens on the West Coast, but not very often.
However, it has now been classified as a strike-slip earthquake.
“So the plates were moving past each other,” says McKinnon.
“Most of the earthquake energy went side to side, instead of moving it up and down, which meant it did not generate a very large tsunami. We did not know that right away, we knew there was an earthquake, it was in a subduction zone, we thought it was one plate going underneath another and it took some time to figure out what was happening.”
University of British Columbia professor and earthquake expert Simon Peacock says residents were lucky the earthquake had a side-to-side movement instead of an up and down.
“It will be about 15 minutes, 20 minutes for the so-called local tsunami, the first tsunami to hit the west coast of Vancouver Island. Certainly enough time to get an alert out, but frankly, if you’re on the west coast of Vancouver Island and the ground has been shaking like mad, pick yourself up and get to high ground.”
Peacock says this should serve as a reminder that we live in earthquake and tsunami territory but that this one could have been much worse.
“Subduction zone earthquakes can produce extremely large tsunamis,” adds McKinnon. “They can be anywhere from centimetres tall, like this one was, to tens of metres tall so it could have been something like the 2011 Japanese earthquake.”
That 9-magnitude earthquake destroyed more than 120,000 buildings and killed more than 15,000 people.
“We can all treat this as a test of how well we’ve set up our emergency notifications,” says McKinnon.
“If you live in coastal B.C. and did not get woken up by an emergency alert, you really need to check your settings so that next time something happens you get woken up so you know to evacuate.”