Assessing the Threat of a Tsunami to the Key Peninsula

Last month marked the 23rd anniversary of the Nisqually earthquake, a magnitude 6.8 convulsion that shook much of the Puget Sound region for nearly one minute in the late morning Feb. 28, 2001.

The epicenter near Olympia was close enough to the Key Peninsula to damage portions of State Route 302 heading toward Allyn, triggered some local landslides, and damaged chimneys and foundations on the KP .

The area hasn’t had a decent-sized shake for a while, especially one that resulted in a tsunami, but experts warn: don’t get too comfortable.

First Warning

Strong shaking is the earliest warning a tsunami may be on its way. Don’t wait for confirmation — get to higher ground immediately.

“That should be the only clue you need to get moving,” said Elyssa Tappero, the tsunami program manager for the Washington Emergency Management Division. “It’s tricky, because you won’t know immediately if it’s caused by a (Puget Sound) fault or the Cascadia Subduction Zone.”

The difference is timing. The KP could see the first wave within 30 minutes if a quake happens underwater in the Puget Sound. A tsunami caused by a large earthquake within the CSZ would take nearly 3 1/2 hours to reach the KP.

“You also won’t know right away if the earthquake caused landslides nearby that would generate damaging waves,” Tappero said. “Good thing about the inner coastal areas is we have a lot of high ground nearby.”

The Shake is Worse Than the Splash

The KP is certainly at risk of tsunamis, but the biggest destruction would come from the shaking. If anything good came from the Nisqually quake, it is that it made Washington state officials reassess building codes and emergency response strategies. Newer buildings should be able to handle a bigger earthquake, but some of the older infrastructure peppered throughout the area may have issues.

Not many people know this, but the Tacoma Fault runs basically along SR 302 as it goes across the Key Peninsula. The Washington Military Department has models on its website showing the potential impact a 7.1 magnitude event would have on the KP and surrounding area.

“You live in a rural area and if something big happens be prepared to be on your own for a while,” Tappero said, referring to a possible lack of emergency services. “Make sure you can take care of yourself and others in your community.” 

Run, Don’t Drive

When an earthquake happens, road conditions may change rapidly. If last month’s windstorms are any indication, expect there to be trees and power lines cutting off major roadways.

If already on higher ground, be prepared to hunker down. If not, don’t rely on a car to get there.

Chris Moore, director at the NOAA Center for Tsunami Research said, “Most of the deaths that happened in the (2011) Japan earthquake were from those in cars.”

Tappero urges those able to move on their own to do so and leave the roads open for emergency vehicles and those who can’t evacuate by foot.

Taking the Hit

The many spits, coves, bays and marinas will take the brunt of the tsunami waves. Moored boats will get pummeled and docks will likely detach. Penrose and Joemma Beaches will be inundated. Being at the head of Henderson Bay, water will funnel underneath the Purdy Bridge and over the roadway, making a mess of Burley Lagoon.

“Waves are attracted to the shallowing that forms a spit,” Moore said. “The area around the Key Peninsula has a lot of passages and inlets that increase the velocity of the waves.”

Moore said damage is made worse because the waves will keep pushing more water into those small areas. As for the Purdy Bridge, “Unfortunately, like all bridges, we won’t know how it holds up after an earthquake until after an earthquake,” Moore said.

Get to High Ground

Just get to higher ground quickly and stay there. There’s no need to leave the Key Peninsula altogether in the event of a tsunami threat. But if it’s necessary to leave, head north. Don’t cross the Purdy Spit after an earthquake. It’s not a place to get caught in a traffic jam. Tappero said that her department is looking to get grants to buy and install more evacuation signs to areas around the KP — especially the spits and state parks — and other inner coastal communities that may be impacted by tsunami waves.

Boaters Beware

“The biggest threat of a tsunami in our area is to the maritime community,” Tappero said. “You don’t want people on the water, in the water, or near the water.”

Save yourself, don’t try to save your boat. Puget Sound is not the open ocean and there really isn’t a safe place to avoid the effects of a tsunami wave.

“Boaters have a hard enough time navigating the normal tidal currents of the Puget Sound,” Moore said. DNR maps show currents, mainly in the passages, surpassing seven knots during a tsunami. Tappero said tidal anomalies will occur anywhere from 24 to 48 hours after an earthquake.

Fascinating To See, But Dangerous to Watch

“You don’t want to go to the shore to see a tsunami,” Moore said, pointing out that it only takes a foot or two of rushing water to knock someone down. “Once you’re off your feet, you’re chances of survival go way down.”

Preparation is Paramount

State and county officials have resources to help prepare for potential disasters like earthquakes and tsunamis. Learn about tsunami preparedness at www.dnr.wa.gov; how to be “Two Weeks Ready” at www.mil.wa.gov; and sign-up for Pierce County ALERT by calling 253-798-6995 or text “PCALERT” to 253-888-777.