The quake-maker you've never heard of: Cascadia
Updated 3:16 PM ET, Thu February 11, 2016 | Video Source: CNN
(CNN) 'Mother Earth' slowly reveals her secrets and this time it's
a fault line deep in the belly of the planet.
Its name is a whopper: The Cascadia
subduction zone.
Its gargantuan size and potential
power amaze earthquake experts, who say it could cause the worst natural
disaster in the history of North America -- if it ruptures entirely.
This quake-maker sits at the bottom
of the Pacific Ocean, where the seabed meets the North American tectonic plate.
In all, it stretches 700 miles along the Pacific Northwest, from British
Columbia's Vancouver Island to Washington to Oregon to northern California's
Cape Mendocino.
In fact, "the Cascadia" already has made history,
causing the largest earthquake in the continental United States on January 26,
1700. That's when the Cascadia unleashed one of the world's biggest quakes,
causing a tsunami so big that it rampaged across the Pacific and damaged
coastal villages in Japan.
Now it's a question of when the Cascadia
will strike again, scientists say.
That big one could "hit at any
time," and there's even a website called Aftershock that
allows Oregonians to enter their address for a custom report on seismic risks.
If the Cascadia were to experience a large-magnitude earthquake, the temblor
and resulting tsunami could kill more than 11,000 people and injure more than
26,000, according to one FEMA model.
The fault line called the Cascadia subduction zone lies in coastal waters spanning 700 miles.
Cascadia
more fearsome than San Andreas
Everyone knows the Cascadia's cousin
in California: the San Andreas Fault. It gets all the scary glamor, with even a
movie this year, "San Andreas," dramatizing an apocalypse in the
western U.S.
Truth is, the San Andreas is a
lightweight compared with the Cascadia.
The Cascadia can deliver a quake
that's many times stronger -- plus a tsunami.
"Cascadia can make an
earthquake almost 30 times more energetic than the San Andreas to start with,
and then it generates a tsunami at the same time, which the side-by-side motion
of the San Andreas can't do," said Chris Goldfinger, a professor of
geophysics at Oregon State University.
The Cascadia is capable of
delivering a 9.0-magnitude quake -- an awesome show of force by Mother Nature.
"You're going to have three to
five minutes of shaking, and if you're used to earthquakes in California, they
typically last 15 to 30 seconds and before you are really sure of what is
happening, it is over," Goldfinger says.
A 9.0 will be different
"In this case, three minutes -- and I've
been in a 9 in Japan -- three minutes is an eternity. It is a very, very
long time," Goldfinger says. "We'll lose a lot of bridges. We'll lose
our highway routes. The coast will probably be closed by down bridges or
landslides or both."
You may as well read this now in case you're ever caught in such a disaster: Rescue crews will be overwhelmed.
"Because
there will be damage to all of the roadway, the various highways,
various infrastructure, and it will be very difficult to get around and
assess what is going on and how you might be able to reach people and
provide them with some of the resources they may need," said Maj.
Richard Ouellette of the Civil Air Patrol's Pacific region.
Revelation of Cascadia's lethality
Prior to the 1980s, the Cascadia was overlooked because it didn't seem to move or cause quakes.
Scientists now know differently.
"The more we learn about it, the less we like it, because it is turning out to be a big hazard as well," Goldfinger says.
To prove that Cascadia has ruptured before, scientists studied the so-called "ghost forests" of the Pacific Northwest.
Underneath
the plants and trees, dirt and mud, is a record of changes to the
landscape. By digging into it, U.S. Geological Survey geologist Brian
Atwater found the proof for one of the world's biggest earthquakes.
USGS geologist Brian Atwater shows a
legacy from when the Cascadia ruptured in 1700: It created a tsunami whose
impact is marked today by a layer of sand atop what was the forest floor, on a
bank near Copalis Beach, Washington.
"The field evidence for the
tsunami here is the sheet of the sand that rests on the floor of the forest
that these trees are rooted in," said Atwater.
He found that after the earthquake,
the coast dropped about 5 feet, and then several minutes later, the tsunami
overtook a spruce forest, bathing it with ocean water. The trees couldn't
survive in the salt water, but many of their hollowed out, dead trunks still
stand today — markers of Cascadia's devastation centuries ago.
Through examining the rings on those
remaining trunks and roots, scientists narrowed down when the Cascadia ruptured
— between 1680 to 1720.
Armed with this information, Japanese earthquake researcher Kenji
Satake turned to diaries and logs from prominent families and
temples of the Shogun era that go back to the 600s. The quest was to find a
record of a tsunami that wasn't accompanied by a storm or a quake in Japan.
Scientists were already curious
about whether a tidal wave could have come from a North American earthquake.
After all, researchers concluded that South American quakes caused tsunamis off
Japan in 1586, 1687, 1730, 1751 and 1837.
From multiple records, it became
clear that an orphan tsunami — devoid of shaking or a storm in Japan — did slam
into its coast in January 1700.
"There are fierce debates in
the scientific community. You know about lots of details, but not about that
main conclusion," Atwater said.
No
way to predict the next big one
Unfortunately, you can't see the
Cascadia fault as you can the San Andreas, which leaves a visible line in some
parts of California.
The Cascadia lies underwater where
the oceanic plate actually dives under the North American Plate. The
"Cascadia subduction zone" derives its name from the Cascade Range of
volcanic mountains that parallel the fault from afar and from how one plate
subducts, or goes under, another.
There's no way of predicting when
Cascadia will author the next big one, Goldfinger says.
"I wish there were, but, no,
there isn't," Goldfinger says. "We can't look forward and say we are
due or overdue really."
Such quakes are the price of West
Coast paradise.
No comments:
Post a Comment