Nepal earthquake sheds light on the Northwest’s ticking clock

Most know the old adage that during an earthquake you should drop and cover. But for those living in the Puget Sound region, there might be a third tip to remember.

“If you feel the ground shake, move up to high ground,” said John Schelling, the earthquake, tsunami and volcano manager with the Washington Emergency Management Division.

“Puget Sound itself has faults that cross underneath it that are capable of generating tsunamis,” he said.

The waters of the Puget Sound flow over a variety of fault lines, Schelling said. And they have the potential of sending big waves to the shorelines of Seattle, Tacoma, Olympia and any community on the water’s edge.

“We get more than 2,700 earthquakes on average (per year) in Washington, believe it or not,” Schelling said. “Most of them are too small to be felt. These deeper earthquakes, like the Nisqually earthquake back in 2001, are felt over a wide area.”

But it’s not just the potential quakes near the Puget Sound that are of concern. Following the disastrous earthquake in Nepal – which killed more than 4,000, and injured more than 9,000 – many thoughts, including those of Schelling, turn to the Northwest. The Nepal earthquake shattered the region at a magnitude 7.8. A magnitude 9.0 has been expected in the Northwest for years.

“Our thoughts and prayers are with the people of Nepal right now,” he said. “They have weathered this catastrophic incident. And we have our own hazards here in Washington that we have to think about, with megathrusts off our own coast, the Cascadia Subduction Zone in particular, and a number of shallow faults across Washington.”

Schelling also noted that it’s not only the quakes within the Puget Sound to consider when thinking about the resulting tsunamis. Studies are underway looking into how a large tsunami might flow through the Strait of Juan de Fuca and into the Puget Sound, following a megathrust in the Pacific Ocean. How significant that wave would be by the time it reaches a city such as Seattle is unknown.

That megathrust isn’t a theory. With fault lines – deep and shallow – crossing throughout the region, it’s something that University of Washington Seismologist Bill Steele is expecting.

“The Juan De Fuca plate is currently locked against North America,” he said. “It produces big earthquakes along that plain every 500 years, on average.”

The last big one was nearly 300 years ago, so the clock is ticking.

“A subduction zone earthquake will produce very strong shaking along the coast, and moderate to strong shaking along the I-5 corridor,” Steele said. “It will take over five minutes to rupture the fault if it starts at one end and runs to the other, at a magnitude 9.0.”

“Now on the coast, they are going to get clobbered by very strong ground motion and very large tsunami waves that will follow,” he added.

While a big one might not happen tomorrow, Northwest residents can expect an earthquake in some form or another.

“Washington is earthquake country,” he said.

Steele said that significant, deep earthquakes – such as the 2001 Nisqually quake – occur every 20-30 years. Those are likely to damage older structures that are not as sound as their modern equivalents. In the surrounding areas, homes may still stand, but what is of more concern is the disruption to services and transportation.

“There’s about an 84 percent chance of another earthquake like the Nisqually earthquake happening, only it could be below Seattle or Everett and produce even stronger ground motion than we saw in 2001,” Steele said.

“The thing to remember is that we are going to survive the next big earthquake,” he said, noting that intelligent preparation is key to dealing with an earthquake. “The chances of being injured or killed in an earthquake are minute. What is going to happen is we are going to be impacted by this – our jobs, our lives our families – with the inability to get around with no food in the stores and no medicine in the pharmacies.”