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Unlike hurricanes, tornadoes
or wildfire, large subduction zone earthquakes are rare,
but they have the potential to cause catastrophic damage
and produce massive tsunamis that can travel the speed
of a 737, that's over 500 miles per hour.
And these tsunamis aren't something you can just ride out.
- Normal ocean waves are produced by wind.
It's almost like you have your coffee cup, it's too hot
and you just blow on it and you create waves on the surface.
But now let's suppose that you put down your coffee cup
abruptly, then what you do is you create a tsunami,
tsunamis, they're generated by a displacement
of the ocean floor.
They move the entire ocean column up.
I mean the wavelength is of the order of several miles.
- And another thing that's particularly
scary about tsunamis,
- So you have this mountain of water that's coming in,
slows down, slows down, slows down.
You sit there looking at it
and suddenly it hits the shoreline and woosh
The tsunami accelerates when it
hits, you know, the dry beach.
- Every coastline around the world is at risk of tsunamis,
but some areas are particularly prone
and they can be deadly.
In 2004, a magnitude 9.1 earthquake off the coast
of Sumatra spawned the deadliest tsunami in modern history,
reaching as high as 100 feet
and killing more than 230,000 people in the west coast
of North America is overdue
for a subduction zone earthquake, the Cascadia megaquake,
which could produce a series of deadly tsunamis.
And here we didn't start planning for tsunamis until well
after we created our whole modern built environment.
So there are just a lot of places
where there isn't anywhere to evacuate to.
So we wanted to know how can you survive a tsunami
and what do you do if there's no high ground?
- There are several communities where the time it takes
to walk is far greater than the estimated wave arrival
- time.
It's a known loss of life.
- Unless we change our course.
The death toll from the Cascadia subduction zone earthquake
and tsunami will almost certainly surpass any other natural
disaster in US history.
So keep watching to find out what the number one factor is
that determines the difference between life and death.
Tsunamis can be caused by landslides, volcanic eruptions,
even meteor impacts,
but their most commonly caused by earthquakes.
And the biggest are caused by subduction zone
or mega thrust earthquakes.
These are earthquakes which occur along fault lines
between tectonic plates.
- It took us a long time
to understand why these big earthquakes were
happening, where they were happening.
The knowledge of plate tectonics is surprisingly recent.
That really became a formally
accepted theory in the sixties.
The earth is made out of these broken up plates,
these shells of crust that are floating
and then sometimes they crash into each other.
And when they crash into each other,
that's a subduction zone.
When Earth formed, it was really, really hot.
You know, four and a half billion years later,
it's still cooling the tectonic plates at the top.
They're the coldest part of the earth
'cause they're the outside rind of the planet,
but the inside is still warm.
So what ends up happening is the plates, as they cool,
they begin to sink back into the earth.
And new warmer material sort of bubbles up to the surface.
It's like a spherical lava lamp
where there's blobs coming up
and then blobs going down just at really,
really slow speeds.
It's about an inch, two inches per year, and that's
- About the speed that your fingernails grow.
- So even though the plates are moving where they touch,
they tend to get stuck just because of friction.
It's like sandpaper.
And so yes, there's an inch of movement every year,
but for 300 or 400 years,
the plates remain stuck at their contact,
which means there's 300 or 400 inches of movement
that were accumulating over the decades and centuries.
And eventually the rocks can't take it anymore.
And when they give way, those 300 inches move.
And that's the earthquake itself.
And that's what creates the really strong shaking
that damages buildings.
That's what creates the tsunami.
That's what wreaks havoc. And
- These subduction zones are found all over the world.
More than 80%
of all tsunamis happened in the Pacific Ocean along what's
known as the ring of fire
and the Cascadia subduction zone along the west coast
of the US has gotten a lot of attention in recent years
because scientists only recently figured out
that it too is capable
of producing massive earthquakes and tsunamis.
- In the eighties
and nineties, scientists started digging in
and looking for past tsunami deposits
and evidence of past earthquakes,
and they found evidence of drowned forests
or ghost forests that indicated
that the land had suddenly changed.
And then they discovered they could date some
of the tree rings from these drowned forests and trees. In
- Cascadia, we know January 26th, 1700 there was at least a
magnitude 8.7 most likely something like a magnitude nine.
And that produced a very big tsunami that you can see today.
If you go and scrape around in the rocks,
you can actually put your finger on sand deposits from the
tsunami here at location on Red Coast.
And it's in historical records in in Japan.
- That's right. The tsunami that was triggered
by the Cascadia mega quake did massive damage
all the way across the ocean.
In Japan,
- They called it the orphan tsunami
'cause they didn't feel the earthquake
and so they weren't sure where it came from.
- And now city officials
and disaster planning experts all across the west coast
are planning for the next one.
Scientists predict that there's a one in three chance
of at least a partial rupture happening
within the next 50 years.
We actually have two videos on this earthquake,
which we'll link below.
But here's a quick description of
what it'll feel like when it happens
- For Cascadia.
We expect for one of these full margin ruptures
that the shaking could last three to six minutes.
If you feel earthquake shaking for a very long period
of time, that's one of your clues
that a Cascadia earthquake has happened
and that a tsunami is coming.
- So when the tsunami starts,
it propagates in both directions.
The speed of a tsunami depends on the depth of the ocean.
The deeper the ocean, the faster the,
that the tsunami travels, the the shallower, the the ocean,
the the tsunami slows down. But
- After combing through amateur video
of the 2004 tsunami in the Indian Ocean,
scientists notice something unusual while
the tsunami slows down.
As it climbs the sloping beach, it actually accelerates just
after hitting the shoreline.
This can give onlookers an artificial sense of security
before inundating the area.
- The tsunami, most of the time looks like a
fast receding tide.
People are not prepared,
- And it's not just one wave.
- Tsunami waves don't just come once they come in a series
of waves and they are kind of like sloshes in a bathtub.
They can get bigger with each incoming wave.
- If you've seen footage of storm surge in hurricanes,
it's a, looks a little bit more like that
where the water just starts rising and keeps rising
and keeps rising and keeps rising
- And with nothing in its way.
It can travel many, many miles inland in Washington state.
It's modeled to travel through the Strait
of Juan de Fuca down into the Puget Sound.
- That means in the event of a Cascadia Megaquake,
even cities like Seattle
and Portland will likely be impacted by the tsunami.
So what's the one factor that determines if you live
or die? REACTION TIME
- The first variable that determines survival rates is
how quickly you move out of harm's way.
- Early warning systems can be helpful, especially
for tsunamis that are generated from a distant earthquake
where you won't feel the shaking.
But for a local subduction zone event,
even the best early warning systems
may not give you enough time.
- Using a combination of GPS
and seismic stations, we measure the earthquake,
then we can say, okay, the earthquake is about this long,
it has about this magnitude.
And so we can make a crude guess that
that's gonna make a tsunami of about that size.
And we can typically do
that in the first five minutes after an earthquake.
- But in the Pacific Northwest, there are places
where the tsunami may hit in as little as 10
to 15 minutes after the quake.
So you can't afford to wait around for those five minutes
when every moment counts. What do you do?
- In all reality, if you feel an earthquake
and you're near the coast or a body of water,
that is your warning that a tsunami may come
and you should evacuate to high ground immediately.
- But that's easier said than done.
- You need to know where safety is,
and that's not immediately obvious.
- You need to be able to react fast,
and that means already having a plan in place
before the earthquake hits.
You should know where high ground is, what's high enough,
and how you're gonna get there.
And perhaps most importantly, you should practice.
And there are helpful tools
with this tsunami evacuation zone map,
which we'll link in the description.
You can input the address of your home
or where you're vacationing,
and it'll tell you where you need to go to get
to high ground and how long
it'll take for you to walk there.
But there are some places where there is no high ground
for miles. Long Beach
Washington is particularly vulnerable.
Its entire population
and all of its businesses are within the inundation zone
and there are communities in Oregon
and California in the same situation.
- Those are really precarious locations.
You'd have to run at Usain Bolt speeds
for 40 minutes sustained to be able to get outta the way.
That's just not going to happen.
- That's where vertical evacuation structures come in.
But we've built shockingly few of them,
just three in the US in fact.
And one of them is the Hatfield Marine Science Center in
South Beach, Oregon.
- It actually sits on a hundred foot foundation.
It is tied to that foundation with 50 foot leg bolts
to make sure that the building
and the foundation stay together during the shaking.
And then when the tsunami wave hits the building, the walls
of the building are designed to fall off
and that will allow the water to move
through the building while we are safe.
On top of the roof, we have a cache of supplies
that will take care of the nearly 1000 people
that are expected to take refuge on top of the roof,
- And they're expecting to stay on top of the roof for up
to two days until the water leaves
and it's safe to come down.
- I make models of tsunamis. This is my job.
I will go and enjoy the beach
and I will just, you know,
point the car in the right direction
and make sure I'm aware of where a hundred feet is.
And I'll look at Google Maps at the topography
and make a little plan in my head of what I would do,
you know, collect the dog and go that way.
- Those people that recognized the signs
and moved immediately away, they were saved.
- There's still a lot that needs to be done
to prepare communities for this inevitable tsunami.
We need more vertical evacuation structures,
more signage and more outreach.
- Let's not be scared. Let's take charge of the situation.
Science and technology are awesome.
If we get together
and do the work, the consequences might be a lot less than
if we just stick our head in the sand
and pretend like la, la, la, la, la.
I can't hear anything. That's a lot worse.
Inaction is the worst decision.
- That's pretty profound, isn't it?
Not only might humans benefit from embracing the sentiment
in regards to the inevitable Cascadia Subduction zone,
megaquake and tsunami.
Perhaps this is a sentiment
that humans would benefit from in general as we continue
to experience natural disasters in ways like never before.
Ignorance is bliss.
But is it best? As I digress, if you're in an area at risk
of a tsunami and you'd like to do what Dr.
Melgar said and take charge of your situation,
here are some things that you can do.
First, be sure to know ahead of time
where high ground or safety is.
Map out and practice your evacuation.
Prepare a go bag with essentials.
Know the signs of a tsunami, be sure to prepare.
Stay safe and see you next time.
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