The final numbers are in, and the Geological Survey of Canada now says yesterday’s earthquake weighed in at magnitude 4.7.
Seismologist Alison Bird says yesterday’s figure was based on quicker, but less representative measurement known as “local magnitude.”
“As time goes on we gather more data and finally do what we call a ‘moment magnitude,’ which is a much more accurate measure of the energy release of an earthquake, but that one takes a long time to calculate, it’s quite labour intensive, so we only got that this afternoon.”
Bird says both the USGS and Canadian agency agree on the final number.
Bird also says if you think you’ve felt an aftershock, you’re wrong. None have been recorded, or are expected because of how deep the quake was, and where it was located.
“Most strong earthquakes you can pretty much be guaranteed aftershocks, especially large subduction zone ones that are shallow. This earthquake’s quite different. For some reason earthquakes within the subducting plate, when it gets down deep, hits the mantle, and this is 50 to 60 kilometers deep this earthquake… we haven’t quite figured this out, it’s a bit of a tectonic mystery, but they don’t tend to have aftershocks.”
Bird says following a quake many people are sensitive, and misinterpret any tremors as being an earthquake.
South coast rattled
Reports of shaking from across the Lower Mainland and Vancouver Island poured in after last night’s moderately strong earthquake.
The Geological Survey of Canada reported the quake hit at 11:39 pm, 21 km NNE of Victoria, at a depth of 60 km.
The National Tsunami warning centre issued a bulletin saying there was no risk of a Tsunami for coastal areas.
— PNSN (@PNSN1) December 30, 2015
People reported feeling shaking from Whistler to Seattle, but as of yet there have been no reports of serious damage or injury.
The quake’s epicentre is in the middle of a geologically active area known as the Cascadia Subduction zone, where the Juan de Fuca tectonic plate pushes under the North American tectonic plate building up pressure – a geological system expected to one day produce “The big one.”
Despite that, Honn Kao with the Geological Survey of Canada says we can’t read too much into today’s quake, but says it’s a good reminder that we should be prepared.
“There is no doubt that this is a very seismicly active area. At this time it is a little bit premature to determine the actual cause of this event, but it’s very likely this event is related to the subduction zone system. You can’t really determine if this is a foreshock or mainshock or any prediction of future earthquakes by having one earthquake here.”
The 4.3 figure clashes with reports from the U.S. Geological Survey, which says the quake measured magnitude 4.8. Kao says the difference comes from the system of sensors used to measure the quake.
“Generally speaking the USGS determine these earthquakes using a much wider network, located far away from the epicenter – and can sometimes give you errors in the location and therefore errors in the depth and magnitude.”
As of yet, no aftershocks have been felt, but the province issued a warning as a precaution.
Be aware of the potential for aftershocks. If you feel one, Drop, Cover & Hold On. Stay there until the shaking stops.
— Emergency Info BC (@EmergencyInfoBC) December 30, 2015
The reaction from officials was swift.
BC Hydro reported no outages or impact to its transmission and distribution network after the shaking.
And TransLink says SkyTrain service was shut down for about an hour as a precaution.
#RiderAlert SkyTrain Expo, M-Line is shutting down due to the recent earthquake until we can determine that our guideway is safe ^jkd
— TransLink BC (@TransLink) December 30, 2015
Representatives with agencies from local government, to police, to search and rescue also went online to call the quake a wake up call, and a reminder about emergency preparedness.
Felt across the region
Within seconds after the tremor, CKNW’s phone lines began ringing with calls from people all across the Lower Mainland.
“It was just terrifying, we have people staying with us right now too, and they were scared. They were running downstairs to our basement screaming and just terrified. They were asking to call their family who are not here so it wasn’t a good scene at all.” – Ahmar Khan from Richmond
“I wasn’t sure what happened, I thought somebody may have hit the building but I knew something was wrong because it didn’t stop, it went on for about 10 seconds of so.” – Ed from Coquitlam
“It felt like a truck hit the building. I was sitting on the couch and wham! the whole building shock, and it only lasted a second” – Shawn from East Vancouver
“It felt like a truck crashed into our house, everything was shaking, you don’t know if it was inside you or around you, it was terrifying. I was looking for the enarest table to go under.” – Dora Kola from Surrey
Social media reacts
The reaction to the quake on social media was immediate, with people weighing in on where they were and what they felt. Reactions ranged from alarm, to humour, to warnings about preparedness.