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Earthquake risk not just a west coast problem

Posted at 7:07 PM, Jan 08, 2020

This week's series of earthquakes served as a reminder that the United States' earthquake risk extends far beyond the Pacific Coast.

On Tuesday, Puerto Rico was rocked by a 6.4 magnitude earthquake. The earthquake knocked out power to most of the island, killing at least one.

Also in recent days, minor earthquakes were felt in Tennessee and Texas.

While there have been dozens of earthquakes with a 4.5 magnitude or higher throughout the United States in recent years, the eastern United States see relatively fewer. Only four earthquakes of 4.5 magnitude or greater in the last four years have impacted the eastern United States.

But the issue is not the quantity of earthquakes in the eastern United States, but the impact.

The USGS puts out a hazard map that shows the earthquake risk nationwide. The map shows areas such as the Pacific Coast and parts of Alaska and Hawaii with a high risk of peak ground accelerations. It turns out that areas of Missouri, Tennessee, Kentucky, Arkansas, Illinois and South Carolina.

USGS scientist David Schwartz agrees that the Pacific Northwest all the way to Charleston, S.C., practically every region of the United States, has a risk of feeling a devastating earthquake.

"The nature of the crust changes as you go from east to west. The Central and Eastern US, the crust is really old, it is older it is colder, it is denser, than the crust in the west which is younger,” Schwartz said. “It’s broken up by many faults and warmer. These different crusts transmit seismic waves differently.”

And this difference in geology means that a strong earthquake in the Eastern United States could cause damage over an extensive area.

Although the Eastern United States has not had many major earthquakes in the last century, two of the most powerful quakes in American history have happened east of the Rockies. The magnitude 5.8 earthquake that caused damage to the Washington Monument in 2011 is only a minor example of the kind of earthquakes the Eastern United States could see.

In 1811 and 1812, a series of earthquakes struck the Mississippi River valley along the New Madrid fault. The strongest of the quakes was a possible magnitude 7.8. The quake was felt across much of the Eastern United States.

In 1866, a magnitude 7.0 rattled Charleston, S.C.

“A repeat of any of those earthquakes would be extremely damaging, because the housing stock in the Central and Eastern U.S. has not been designed for earthquakes,” Schwartz said.

According to a survey funded by the U.S. Army, a magnitude 7.7 earthquake located along the New Madrid fault could cause 85,900 deaths and $298 billion in damage. By comparison, Hurricane Katrina caused roughly 1,500 deaths and $110 billion in damage.

What to do during an earthquake

  • DROP to the ground (before the earthquake drops you!),
  • Take COVER by getting under a sturdy desk or table, and
  • HOLD ON to it until the shaking stops.