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Earthquakes in the U.S.

Not just a West Coast phenomenon

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February 14th, 2018
Damaged buildings along Tradd Street in Charleston, S.C., show the destructive power of an earthquake.

Damaged buildings along Tradd Street in Charleston, S.C., show the destructive power of an earthquake.

 

If you live near the mid-Atlantic coast, you may have noticed it. On Thursday, November 30, 2017, at 4:47 p.m., doors and windows rattled, tree branches shuddered, and floors vibrated as a 4.4 magnitude earthquake shook the region.

The tremor’s pulse, which only lasted a few seconds, registered as far north as New York City and as far south as Northern Virginia. Seismologists have identified the epicenter as being about six miles east-northeast of Dover, Del., with no reported damage.

The quake jolted those who felt it, sending a clear message that such events are not necessarily confined to states like California. In fact, the East Coast has had its share of earthquakes over the last 380 years—some of them rather severe, even by West Coast standards.

In 1638, for example, an earthquake that seismologists surmise was centered somewhere around New Hampshire or Vermont hit with an estimated 6.5 magnitude. In 1755, another quake rocked nearby Massachusetts with a magnitude of 6.2.

And these are just a few of the big ones. Various estimates indicate that the New England region alone has 100 small earthquakes each year; although such occurrences are by no means unique to the North East.

On August 31, 1886, Charleston, S.C., experienced a violent 7.3 magnitude quake that killed 60 people and damaged 2,000 buildings from Charleston to Richmond, Va. Since 1977, this area has had 200 additional minor quakes, with a not-so-minor shocker in 2011.

Centered 38 miles northwest of Richmond in the town of Mineral, Va., this latter quake reached a 5.8 magnitude and was felt as far away as Canada. 

If these events tell us anything it’s that earthquakes can occur anywhere. 

The globe is laced with fault lines, many of which remain unknown to scientists. Not until the mid 1990s did researchers locate the fault responsible for Charleston’s deadly 1886 quake. 

But one thing seismologists know for sure is what goes on underground during an earthquake.

Below the surface

“To understand what actually happens during an earthquake, you have to frame your understanding of the planet as a whole,” says John Armbruster, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory. “Remember, the Earth is not a static ball that’s frozen stiff.

“It’s dynamic; its surface moves.”

Deep within the Earth, conditions are extremely hot. At its core is a roiling, lava-like mass that emanates enormous heat and pressure, causing the upper layers of the planet’s crust to shift.

Called “plates,” these layers are separated by large cracks or faults. When plates move, their edges press against one another, building tremendous energy, the release of which causes an earthquake.

That’s why states such as California experience quakes so frequently. 

“North America is pretty much one big solid plate,” explains Armbruster. “This North American plate is moving relative to the Pacific Ocean plate, and they’re scraping against each other. 

“A great example is the San Andreas Fault.”

Here, shifts in the Earth’s crust are significantly greater than on the East Coast, in part because the North American continent is literally sliding to the Southwest. As it moves, it squeezes faults like the San Andreas, resulting in the intermittent build-up and release of energy.

Past earthquakes along this fault are testament to the incredible force involved. 

Seismologists believe the famed San Francisco earthquake of 1906 reached a magnitude 7.8, killing over 3,000 people. Remarkably, the shaking was so intense that, in nearby Monterey County, it permanently altered the course of the Salinas River by six miles.

“Some earthquakes are barely perceptible, but in the case of the really big ones, you’re dealing with a catastrophic amount of power,” says Armbruster. “The 2004 earthquake off the coast of Sumatra was about a magnitude 9, which is more energy than all the nuclear weapons on Earth.”

Perhaps more troubling is our inability to anticipate such incidents. 

Not so easy to predict

Despite the wealth of technology currently available to scientists, Armbruster says there is no dependable method for predicting earthquakes, big or small.

“There is no routine formula that truly works,” he explains. “Seismologists have made some educated guesses, speculating, for instance, that San Francisco won’t see an earthquake like 1906 for another 100 or 200 years.

“But who says it has to happen at the 200 year mark? Observation suggests that energy can build up quietly and without warning before it’s released.”

That said, Armbruster further points out that earthquakes are generally nonrandom episodes, with approximately 70% of them occurring within the Pacific region. Still, the quakes in South Carolina, Virginia, the New England states, and most recently Delaware serve as reminders that the East Coast is not invulnerable. 

After all, our planet is constantly changing, and sometimes, we can feel it under our feet.

 

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