Kind: captions
Language: en
In this region, a massive earthquake is
pretty much inevitable.
This is the Cascadia subduction zone.
It's one of the top hazards on the
planet. Here, the ocean floor is slowly
diving under North America. Massive
earthquakes are expected here every 500
years or so, and the last one was in
1700.
>> So, it's not a matter of if, it's just a
matter of when.
A 2025 study suggests that the quake
could suddenly sink part of the Pacific
Northwest and climate driven sea level
rise would only make it worse.
So why is the Cascadius abduction zone
so dangerous? And when will the next big
one happen?
The Cascadius Abduction Zone is a major
fault line that spans Vancouver Island
in Canada to Northern California. But
it's not really a line at all. It's a
crack where two massive tectonic plates
meet. It's where one of the largest
earthquakes in the history of North
America happened more than 325 years ago
in January of 1700. The earthquake had
an estimated magnitude of 9 and it
caused a tsunami.
A graveyard of trees that fell victim to
flooding are still in the area, but the
subduction zone has been pretty quiet
ever since.
The last magnitude 9 earthquake on Earth
was caused by a subduction zone known as
the Japan Trench in 2011.
It spurred a tsunami and caused
widespread devastation, including a
nuclear disaster at the Fukushima Daichi
power plant.
Subduction zones produced the biggest
earthquakes in the world. They happen
where one tectonic plate is sliding down
another plate. In Cascadia, you have one
plate diving down beneath another. This
section gets locked and it pushes this
part up. When the fault ruptures, when
the amount of stress overcomes the
friction, it bounces back, which lifts
up the water above it and causes that
water to flow out in all directions. And
that water flowing out in all directions
is the tsunami.
>> The inevitable earthquake in the Pacific
Northwest is what's called the big one,
and it would absolutely be devastating
to a number of coastal communities. But
the Cascadia subduction zone is not
actually one continuous fault line. It
has ruptures in it that form at least
four major segments. It's possible that
an earthquake in one zone might not
trigger an earthquake in the others, but
the longer the segment, the bigger the
quake. One segment runs from Vancouver
Island to the Oregon border. Some
scientists think that this is the most
dangerous section and could spark the
biggest earthquakes.
So, when will this happen?
Unfortunately, earthquakes often happen
without any clear warning signs, and
scientists haven't yet identified
reliable predictors. The United States
Geological Survey even says that quote,
"Neither the USGS nor any other
scientists have ever predicted a major
earthquake and that they do not expect
to know how to predict earthquakes in
the foreseeable future." Wo!
Even if scientists can't predict when an
earthquake will strike, they can use
analytical models to study the potential
effects. Some researchers found that if
the Cascadia earthquake were to strike
today, the coastline could suddenly sink
by up to 6 f feet, raising the sea level
and more than doubling the number of
people, buildings, and roads currently
exposed to coastal flooding risks. Sea
levels are already rising across the
globe. But the Pacific Northwest coast
has seen much slower rise than other
parts of the US coastline because of the
subduction zone. It's slowly pushing the
coastline up almost as fast as the sea
level is rising in some areas. But a
massive earthquake could quickly reverse
that. According to one projection, by
the year 2100, sea levels along the
Pacific Northwest could rise by almost 3
ft. Combined with the Cascadia quake,
that's a sea level difference of nearly
9 ft compared to today. And don't forget
that when the earthquake strikes, it
will trigger a tsunami, which could
bring waves over 50 ft high in some
locations.
For now, some communities are taking
action against these deadly threats by
creating high ground. A tsunami could
come only 15 minutes after an
earthquake, and experts say it's
imperative to get to high ground ASAP.
The thing is that in many low-lying
coastal communities, that isn't an
option. So, vertical evacuation
structures like towers and platforms
where people can get to high ground
without traveling great distances are
essential. Right now, there are three
vertical evacuation towers in the
Pacific Northwest. A tsunami evacuation
tower built by the Shaw Water Bay Indian
Tribe, an elementary school gym that was
rebuilt with the fortified foundation to
withstand massive earthquakes, and a new
roof built to hold more than a thousand
people, and an Oregon State University
marine sciences building. There are more
vertical evacuation structures planned
for the Pacific Northwest, but one study
found that many more are needed. The
trouble is, we don't know how much time
we have until the next big one.
[Music]
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