Cascadia earthquake occurred along the Cascadia subduction zone on January 26
with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake
involved the Juan de Fuca Plate that underlies the Pacific Ocean, from
mid-Vancouver Island in British Columbia, Canada, south along the Pacific
Northwest coast as far as northern California. The length of the fault rupture
was about 1,000 kilometers (620 miles) with an average slip of 20 meters (66 ft.).
earthquake is happening under Puget Sound right now, which increases the risk
of a Cascadia subduction zone earthquake.
— Although the risk is slight, it might be a good time to check your supply of
food and fresh water. That’s because the region is entering a period when the
risk of a megathrust Cascadia subduction zone earthquake is slightly higher.
Wednesday, the semi-annual “slow slip” event began, according to the
Pacific Northwest Seismic Network (PNSN) at the University of Washington. The
event happens about every 14 months deep underneath the Puget Sound area and is
essentially a slow earthquake that takes place over the course of two weeks.
slow-slip event, after 14 months of moving eastward, the Juan de Fuca tectonic
plate stalls and moves westward, which puts stress on the Cascadia subduction
often refer to this as a “straw that broke the camel’s back”
loading up the edge of the lock zone of the Cascadia subduction zone more
rapidly than normal tectonic processes would do,” explained Bill Steele,
director of communications at the PNSN. “You’re getting seven months of
strain accumulation applied to the back edge of the fault over a week.”
probability of a Cascadia quake goes up during a slow-slip event, but just
slightly more than during other times of the year, Steele said. Still, it’s not
a bad idea to check your emergency plan and make sure you’re ready for a large
there are small tremors vibrating up and down the eastern edge of the Olympic
Peninsula. The small tremors happen every few minutes. You can see a live
scroll of tremors on the PNSN website.
also the risk of other types of earthquakes. On Wednesday night, a magnitude
4.2 earthquake hit near Belfair, about 34 miles west of Seattle. That’s a
relatively large quake for the region, and it could be a precursor to a larger
earthquake along a local fault. Over the next 48 hours, there’s the risk of a
larger 5 of 6 magnitude quake. The Seattle fault, which runs from Fall City
through Seattle to Bremerton, is capable of producing a powerful magnitude 7.0
A full rip of the Cascadia subduction zone would be a devastating event up and down the West Coast. The subduction zone extends from Eureka, California, to mid-Vancouver Island. A Cascadia event could cause up to a 9.0 magnitude quake with intense shaking lasting up to five minutes. The shaking would level un-reinforced buildings and roadways, sever utility lines and rupture gas and oil.