Possible megaquake brewing in Washington

On July 20, 2015, the New York Times published an article by writer Katherine Schultz under the headline, “The Earthquake That Will Devastate Seattle,” popularizing talk of the Cascadia Subduction Zone throughout the nation. Located miles off the coast in the Pacific Ocean, the subduction zone stretches from Vancouver Island in Canada to Northern California, and occurs where the Juan De Fuca tectonic plate slips beneath those of continental North America.

Cascadia Subduction Zone

The coastline all along the Pacific Ocean, known as the Ring of Fire, includes geologically violent subduction zones. As one plate is pushed down by the other into the mantle, rock liquefies and expands, creating many of the West Coast’s active volcanoes. Further, the process isn’t consistent, and earthquakes are often caused by a plate slipping.

“If the entire zone gives way at once,” Schultz wrote, “an event that seismologists call a full-margin rupture, the magnitude will be somewhere between 8.7 and 9.2. That’s the very big one.”
Japan, which also lies inside the Ring of Fire, experienced a magnitude 9.0 earthquake in 2011, which devastated homes and infrastructure. However, the majority of the 19,000 dead were killed by the resulting tsunami, which also lead to the nuclear reactor meltdown in Fukushima.

Schultz opened her article on the Cascadia Subduction Zone with an expose on the devastation felt by the Japanese, drawing comparisons between the two countries and their geological positions.
“What is extraordinary is that all of Cascadia is quiet,” said University of Oregon Geophysics Professor Doug Toomey in an interview, “It’s extraordinarily quiet when you compare it to other subduction zones globally.”

“The lack of inter-plate seismicity is interpreted to reflect complete healing and locking of the megathrust over three centuries after the previous great earthquake,” wrote Koichiro Obana and his co-authors in a paper for the Bulletin of the Seismological Society of America.

The great earthquake and resulting tsunami which occurred over three hundred years ago buried the coast so completely that geological evidence of its occurrence was not discovered until the 1980s. Previously, geologists could not understand the lack of low- or mid-level earthquakes in the Northwest, which lies along the Ring of Fire and thus should logically have seismicity comparable to Japan or California. Since the slip of 1700, the two plates have been in a state of stasis with each other, the Juan de Fuca plate locked against the continental plates, neither budging or giving way.

“If there were low levels of offshore seismicity, then we could say some strain is being released by the smaller events,” Toomey said. “If it is completely locked, it means it is increasingly storing energy and that has to be released at some point.”

Scientists at the Federal Emergency Management Agency are therefore speculating that the next great quake could result from the Juan De Fuca violently breaking through its lock, where the entire border slips as opposed to just the north or south side. In this worst-case scenario, a FEMA official interviewed by Schultz claimed, “Our operating assumption is that everything west of I-5 would be toast.”

“I think by saying the region will be toast,” Schultz said in a subsequent interview with Here and Now’s Meghna Chakrabarti, “part of what he’s getting at is actually the fallibility of the infrastructure. When you think about it, there’s not that many roads over the mountain passes, you take one out and suddenly you can’t access these, you can’t get in there to help people. It’s not that every building is going to collapse and every person is going to be underneath it, it’s that we have a huge logistical problem of even providing aid.”

If the megaquake were to occur, Bellevue College Public Safety recommends, if one is indoors, to stay indoors, taking shelter under a desk or table along the inner wall. If one is outside, Public Safety advises students to avoid electric wires, poles or anything that may fall. Students should avoid glass walls, windows, outside walls or outside doors.