Roughly every 14 months the Pacific Northwest goes through a seismic cycle known as a slow-slip event. For about a two to four week period the region will experience thousands of small earthquakes, unfelt to the residents of the region. However, not all the earthquakes associated with slow-slip events go unfelt. Residents of Vancouver Island and the BC Lower Mainland will no doubt remember December 29, 2015 when a 4.7 magnitude quake struck in the late hours of the evening near Victoria rattling houses across Southwestern, BC. If you didn’t feel it, you sure heard about it at work or on social media. It was the talk of the town for weeks following the event. The tremendous overreaction of residents showed how drastically under-prepared and in denial many of us are.
This quake was one of almost 8000 earthquakes during the last slow-slip cycle, which occurred from December 22, 2015 to January 16, 2016. I’m sure some of you are already using your hands to count out when the next slow-slip event is going to happen. I’ll save you the trouble. 14 months from December 22, 2015 would be February 22, 2017, but since the 14 month window is approximate the next slow-slip cycle could start any day now. In fact, according to the Earthquake Early Warning British Columbia Facebook Page it may have already started, yesterday. The page is run by Kent Johansen a Research Engineer at UBC, and he's been keeping a very close eye on things in anticipation of the next slow-slip cycle.
In a CBC article last fall, Alison Bird, an Earthquake Seismologist for the Geological Survey of Canada, said "What we think is happening is that whenever there's that reversal… it's loading extra stress onto the locked zone… It could be a last straw scenario, just that little bit of extra stress that’s going to cause that rupture to trigger … the megathrust earthquake.”
Now this isn't to say that the Big One could only happen during a slow-slip event, but the odds are significantly higher that it will. Kind of like how the odds of getting in a car accident are increased during rush hour or bad weather.