Earthquake News

Seattle will undoubtedly be ravaged by a devastating earthquake at some point. Here's how to get through it.

The New Yorker released an article in 2015 claiming that an earthquake in our portion of North America — the eventual big one — "would spell the continent's biggest natural tragedy." People in this town didn't want to think about it.

Nonetheless, When the shaking starts, "everything indoors and unsecured will lunge across the floor or come tumbling down," according to the New Yorker. Houses that aren't anchored to their foundations will fall apart.... A million buildings, including more than 3,000 schools, will collapse or be harmed. Half of all highway bridges, two-thirds of railways, and two-thirds of airports will be affected, as would one-third of all fire stations, half of all police stations, and two-thirds of all hospitals. Landslides will occur over the region as a result of the quake. Fires, flooding, pipe breaks, dam breaches, and hazardous-material releases will result from the sloshing, sliding, and shaking. Then will come the wave, and the true destruction will begin."

A earthquake is also the theme of my story. My area of concern, however, is far narrower than that of The New Yorker, which is concerned about a quake that will wreak havoc on a large chunk of the coastal Northwest. I'm concentrating on one that will only wreak havoc in Seattle and its surrounds.

This is a trigger warning. I'm about to go into great depth about several things that might frighten Seattle residents. Why would I do such a thing? Because many of us here read a story in The New Yorker and then did little or nothing to prepare for an earthquake. That will almost certainly happen as a result of this post. However, I hope it is not for everyone who reads it.

The world as we know it is divided into fragments, despite the fact that it appears to be unbroken and continuous. These chunks are referred to as "plates" by geologists, but I can't imagine them that way because they're around 60 miles long from bottom to top. They resemble blocks more than anything else.

The North American block, on which Seattle is situated

, ends to the east in the mid-Atlantic Ocean and to the west fewer than 150 miles off our coast. The Juan de Fuca block is located just west of it. According to all reports, these blocks are being pushed together by inexplicable forces. Because they're in each other's way, something has to give — and it does, on a regular basis. The next time something gives at these plates, as described in the New Yorker piece, something bad will happen. It clarifies what it means when all hell breaks free as a result of it.

If you reside in Seattle, however, you can rest easy knowing that the precipitating events will occur roughly 175 miles west and several miles beneath the surface – in other words, far enough away to mitigate the worst consequences. The nightmare that will befall Seattle will not contain as much intense shaking — or tsunami inundation — as the shores of Washington and Oregon will. Even still, when the tremors subside and the sea returns to normal, Seattle will be in a difficult situation.

But it's The New Yorker quake, a regional catastrophe that will wreak havoc on tens of thousands of square miles, including our city. When it happens — as it must — the one I've been unable to write about will very certainly be the one I've been unable to write about thus far.

THE TEN LARGEST EARTHQUAKES IN THE WORLD BETWEEN 2012 AND NOW have all been of The New Yorker variety, also known as megathrust quakes. The precipitating events took place deep beneath the bottom in each case. One quake occurred in the Indian Ocean, while another occurred beneath the Sea of Okhotsk. The other eight all began their journeys beneath the Pacific Ocean. A total of 137 people were killed as a result of these ten earthquakes. If that number doesn't seem modest, consider that the largest earthquake in 2011, which was also a megathrust, killed nearly 20,000 people.

Why did one quake kill so many people more than the others? The ten most powerful earthquakes in the last decade occurred so far from land, both vertically and horizontally, that by the time their impacts reached populated areas, they were too weak to kill huge numbers of people. The 2011 quake, known as the Great East Japan Earthquake, began distant from land but had terrible consequences, including a tsunami. When a quake occurs where the Earth's blocks collide, the ability of the quake to kill depends heavily on one element: a tsunami. If the quake isn't particularly strong, there will likely be few casualties. If a large tsunami occurs, the death toll could be substantial. That was the case in 2004.

When the next megathrust quake strikes the coastal Northwest, Seattleites can rest assured that Puget Sound will not be roiled in the same way that the Pacific was roiled by the Great East Japan or Indian Ocean earthquakes. There will be a great deal of pain and deaths, but no apocalyptic devastation.

I DON'T WANT TO MISLEAD THE WARNING OF THE NEW YORKER. The impending megathrust quake it portrays is cause for concern, not only because of the horrors it would bring, but also because it may occur soon. Quakes of this magnitude strike our region every 500 years on average. The most recent one occurred 322 years ago, while the one before that occurred approximately 1,300 years ago. If you're a cup-half-full person, you can opt to concentrate on the fact that nearly 1,000 years transpired between the two. For the rest of us, it may come as a shock to learn that there was a 320-year gap between the earthquake of 1,300 years ago and the one before it.

The Richter scale, which has been replaced by the "moment magnitude" scale, gives these megathrust quakes a very high rating. Scales like these are designed to convey information about the relative power and severity of earthquakes, and they are extremely important to geologists. The scales, on the other hand, can be deceiving in ways that can have serious ramifications for the rest of us.

The magnitude of earthquakes is emphasized in news reports. They keep reminding us of the magnitude of what transpired. They utilize numbers in addition to accounts of death and damage – how many people were killed, how many were injured, how many were displaced, and how many buildings were leveled. A one-digit whole number followed by a decimal, such as 9.2 or 6.2, looms over it all. Those are numbers on the moment magnitude scale.

The instant magnitude scale denotes events that increase in intensity by one-tenth of a whole number at a time. In other terms, a 9.2 earthquake would be almost a third more powerful than a 6.2. However, because the moment magnitude scale is logarithmic, this isn't the case. A 9.2 is tens of thousands of times stronger than a 6.2.

It might not matter if that was all there was to it. We'd mistake the meaning of numbers in a way that was harmless to us. Unfortunately, there is a more serious issue at hand. The depth and position of a quake, which have a lot to say about its potential for destruction, are ignored by scale numbers.

The next significant megathrust quake in this area will again originate deep beneath the Pacific seafloor. The next large quake in the Seattle Fault Zone, however, will occur at a shallow depth just beneath our metropolis. The megathrust quake will be a 9 on the Richter scale, while the Seattle quake will be closer to a 7. Don't be soothed by your interpretation of the scale figures (even though a 9.0 is more than 1,000 times more powerful than a 7.0 when you do the arithmetic). In Haiti, a 7.0 earthquake killed over 300,000 people in 2010. That one began 6 miles beneath the earth's surface. It struck 16 miles from Port-au-Prince, a city roughly the size of Seattle.

THESE ARE DIFFICULT THINGS TO CONSIDER RATIONALLY. Most of us have taught our brains to lead us to specific results because we prefer them. Our conclusions come first, followed by arguments in support — for example, "No large earthquake will occur during my lifetime." As a result, we willingly affirm our biases. We bury our heads in the sand after that.

Seismologists estimate that the chances of a 9.0 earthquake striking the coastal Pacific Northwest in the next 50 years are roughly 14%. Perhaps you'll accept those chances and wager that it won't happen. After all, they're not bad: they're about as likely to miss a 37-yard field goal as an NFL kicker. On the other hand, the odds of Donald Trump defeating Hillary Clinton were approximately the same – 15% (as predicted by The New York Times on Election Day morning, 2016).

In the Seattle Fault Zone, the chances of a 6.5 quake in the next 50 years are 5 percent. You might wager against it happening based on those odds. By betting against it, I mean failing to plan for it. The majority of people are taken aback whenever an earthquake occurs.

GEOLOGY YET AGAIN.

The Juan de Fuca block revolves in a cylinder-like fashion. It seeks to grind through the neighboring North American block as it moves eastward on its descending arc. The interpenetration zone of the blocks is located beneath the Cascade Range, where high pressures form volcanic peaks like as Mount St. Helens, Baker, and Rainier. However, the leading edge of the North American block, which is being forced west, carves material from the sinking Juan de Fuca block and piles it as rubble.

In Western Washington, we live on top of Juan de Fuca block rubble, interspersed with a massive amount of material that has been sliding off the North American block for a long time, all of it now packed nearly solid and subject to its own set of earthquake-causing pressures.

Within this admixture, the Seattle Fault Zone is made up of blocks pressing against one other, just as the admixture beneath it. It stretches 40 miles east to west and 5 miles north to south, and contains a significant fracture just south of downtown and another fracture beneath a series of North Seattle neighborhoods. The zone, which is located at a depth of 2 to 4 miles, is prone to earthquakes such as the one that struck Haiti or the 6.9 earthquake that struck Kobe, Japan, in 1995, killing thousands of people and causing more than $100 billion in damage. As it turns out, the geologic conditions beneath Seattle are very similar to those beneath Kobe.

The events in Kobe were disastrous. At least 80% of the approximately 6,400 persons that died in the city and its environs died trapped in rubble. In firestorms, some people were crushed, smothered, and died. Fortunately, the shaking began before 6 a.m., so most places of business were closed. Despite this, over 40,000 people were hurt and 240,000 homes were damaged. Hospitals were bursting at the seams. It was January, and the weather was bitterly cold. Approximately 300,000 individuals became homeless as a result of this. I won't go on, but I will note that it all happened in a country that is largely regarded as being at the forefront of earthquake preparedness. And that the epicenter of the quake was 12.5 miles away from the city and 10 miles away from the epicenter of the quake.

Earthquakes in the Seattle Fault Zone start as ruptures. The strain of opposition becomes too severe at some point along one of its faults or fractures — by which I mean a seam where two blocks shove against each other — and one or both blocks abruptly move. When this happens, the energy released spreads in all directions, but most notably along the tearing fault itself.

Imagine two blocks coming together on a diagonal line: Two things can happen if the fault ruptures. One of the blocks has the ability to climb. Alternatively, one person can climb while the other sinks.

Ready to retrofit?

Let’s make your home safer

Get a professional evaluation

Call 206-352-5644

 

Sound Seismic
7543 15th Avenue NW
Seattle, WA 98117

Contractor's license # SOUNDSL836ND

© 2022 Sound Seismic
Seattle Website Design