Friday, April 30, 2010

[Geology2] Is Arkansas at risk for an earthquake?

Is Arkansas at risk for an earthquake?

Reported by: Justin Earley
Last Update: 8:51 am

We see the images jumping out of our TVs, the catastrophic damage from massive earthquakes. In Haiti, Chile, and Mexico, the quakes claimed lives and leveled buildings.

But what about the storied New Madrid Fault the runs through northeast Arkansas? It actually re-routed the Mississippi River in the early 1800s. But do these recent events point to a major quake here?

With the New Madrid seismic zone extending all the way from Cairo, Illinois to Marked Tree in northeast Arkansas, could we expect a major earthquake here and what would it do? To find those answers you need to go back in time.

From 1811 to 1812, the New Madrid Fault line gave us three of the most powerful earthquakes in U.S. History. It reached a magnitude of 8.0 on the richter scale and rang church bells all the way to Boston. In New Madrid, Missouri, cracks opened up in the ground. The earth's surface visibly rolled in waves and The Mississippi River actually did flow backwards. The damage nearly wiped New Madrid off the face of the Earth.

UALR PhD candidate Okbar Al-Qadi showed the reason damage can be so intense. Sandy areas do a much poorer job of absorbing quake vibration than rocky ones so the waves travel farther and cause more damage. In much of eastern Arkansas, that's nearly all we've got.

Those at UALR say they discovered a fault line south of Marianna. About 5,000 years ago, they say a pretty good sized earthquake here caused what they call sand blows, like little volcanoes of sand and water shooting up through the ground because of the intense shaking and pressure.

That is still a concern around the New Madrid Fault itself, but the bigger worry is sandy sediment giving way beneath roads, homes and other buildings across the state.

Dr. Haydar Al-Shukri at the earthquake center at UALR says the number of earthquakes isn't higher this year; the quakes are just striking more populated areas. And they're all unrelated since they're on different fault lines. Still, Dr. Al-Shukri believes we have a 50 percent chance of experiencing a 6 or 6.5 quake somewhere along the New Madrid in the next 15 years.

"The more we wait, the more the probability increases because we know stress is accumulating. We see it because minor activity takes place along this fault," says Dr. Al-Shukri.

So what would a big New Madrid quake do?

If a 6.5 magnitude quake happened at the southern part of the seismic zone in Marked Tree, northeast Arkansas would see major structural damage, loss of power and water, injuries, and death. In Little Rock, you'd see structural damage, especially in places built on soft sediment close to the river or in the eastern part of the city.

"We don't know what bridges will be up, we don't know what roads will be passable," says David Maxwell. "A lot of the efforts at first will be assessing what has actually happened."

The Arkansas Department of Emergency Management (ADEM) would jump into action to respond to earthquake damage. In fact, it's preparing for a 7.0 quake scenario. Emergency responders drill regularly and ADEM is making sure agencies have enough resources like food, water and medical supplies to meet all the needs. A massive 2011 drill marking the 200th anniversary of the first New Madrid quake happens next year involving all eight states that could be impacted by a New Madrid quake.

On top of the drills, retrofitting projects are happening at bridges and buildings across the state, particularly in the northeast, to stabilize these structures and protect them from an earthquake's vibrations.

"Our attitude is that we've got to get prepared now because it could happen tomorrow," says Maxwell.

Until then, the Earthquake Center and the Arkansas Geological Survey are in the process of placing more seismic stations across Arkansas, a total of 14, to monitor activity. While an increase in activity doesn't always happen before a major quake, pre-shocks in the hours before a quake can sometimes provide a life-saving warning. But experts say, make no mistake a big one is coming someday.

"This is not just my interpretation of what's going to be happening. This is the interpretation of almost all geologists and seismologists who study the region," says Dr. Al-Shukri.

What you can do at home to be prepared?

  • Keep several days of food and water stockpiled in your home.
  • Minimize damage and injury in your house by securing bookshelves, hot water tanks and other heavy items to your walls.
  • Move heavy objects around your home from top shelves to lower ones to keep them from falling and hurting anyone.
  • Find out if your home has earthquake coverage since most homeowners' policies in Arkansas don't cover it.
Very good video on the NMFZ here at source--click me

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