New Madrid Earthquake Bicentennial

[Start of Audio]

[Earthquake simulated sound - crash of falling debris, car horn, alarms -  audio mix]

Newscaster 1:  Is that an earthquake?

Dr. Michael Blanpied:  The thing about earthquake and earthquake hazards are they're so preventable. If we build good buildings, there's no reason any building should collapse. There's no reason any person should die from an earthquake. And yet, people will die, buildings will be damaged and there's a lot of work both to understand what needs to be done to reduce those hazards—to make people safer—and then also, to provide information to people in a way that will convince them to actually take the steps necessary.

[End of Audio]

Ray Douglas:  That's Dr. Michael Blanpied, Associate Coordinator for the USGS Earthquake Hazards Program.

Join us today as we discuss the New Madrid Seismic Zone. I'm Ray Douglas and this is CoreCast, your science podcast for a changing world.

Mike, thanks for joining us today.

Dr. Michael Blanpied:  Nice to be here.

Ray Douglas:  What is the New Madrid Zone and where it is located?

Dr. Michael Blanpied:  Well, the New Madrid Seismic Zone refers to an area in the Central US, lying along the Mississippi River that has a lot of earthquake hazards. The area actually covers about eight states: Missouri, Tennessee, Arkansas, Kentucky, all the way up to Indiana, Illinois and down south into Southern Arkansas.

Ray Douglas:  So why are the earthquakes in this region so different than those occurring in the west, say, on the Pacific Coast?

Dr. Michael Blanpied: In the Western US, earthquakes are, of course, frequent. But the seismic waves that come out of those earthquake faults don't travel very far through that young broken up rock. So we have intense shaking right around the earthquake and then it dies off with the distance rather quickly.

Not so in the Central and Eastern US. Here the rocks are old and cold and they really ring like a bell when an earthquake strikes and the seismic waves can travel quite far. Those earthquakes can actually be felt over perhaps half the United States.

Ray Douglas:  Is there an example of that?

Dr. Michael Blanpied:  The February 1812 earthquake, which was probably in the 7.0 to 7.5 range, in magnitude, was felt all the way to the East Coast, in the Carolinas. That's an incredible distance for seismic waves to carry with enough strength to be felt.

Ray Douglas:  I understand that this region is vulnerable to something called liquefaction. Can you tell us what that is?

Dr. Michael Blanpied:  What liquefaction is, is when you have a saturated sandy soil and you shake it, the soil can actually behave like a Jell-O. The water and the sand become suspended and the soil loses its bearing strength and can actually flow. And when that happens, if there's a building sitting on a liquefied soil, it can actually sink or tilt. A bridge abutment built on a liquefied soil will tend to shift.

And another thing that happens is that sometimes, this liquefied sand can erupt out on to the surface in what we describe as a sand blow or a sand volcano and we can have ponds of water and sand formed all over the landscape. It can be quite a hazard in areas like the Central US where there is a lot of saturated soil.

Ray Douglas:  Are there any other water-related post-earthquake effects that might affect this area?

Dr. Michael Blanpied:  There are really a number of different effects that the earthquake can have if it's a large one. Sloped areas can have landslides, river banks can collapse and clog the channel making the water divert or making shipping difficult. It can also have fires that can break out and be difficult to put out if the water system is compromised. It can have hazardous wastes that are spilled by the rupturing of tanks or whatnot.

Ray Douglas:  What observations are pointing toward to a New Madrid event actually occurring and what are the latest predictions?

Dr. Michael Blanpied:  We've studied the likelihood of earthquakes at various size in the Central US, in particular, the New Madrid Seismic Zone. We have ongoing earthquakes that don't seem to be slowing down. These are the smaller ones.

And we also have a geologic historic that shows that these large earthquakes occurred many times in the past. We estimate that the likelihood of a magnitude 6.0 earthquake, which would cause damage in a local area, is something on the order of 25% to 50% over their coming a few decades.

The likelihood of a magnitude 7.0 earthquake, something like the 1811, 1812 earthquake, that's something on the order of 10% or one chance in ten that will happen over, say, over the lifetime of buildings that are now being constructed.

Ray Douglas:  Aren't the New Madrid Zone earthquakes difficult to predict?

Dr. Michael Blanpied:  Yes, we are still struggling to understand exactly how these earthquakes occur and where and when they might occur again. But, goodness, this is the time when we should be making sure that we're ready for those earthquakes if they happen again.

Ray Douglas:  Mike, what guidance or products does the USGS Earthquake Hazards Program provide right now that can help America make better decisions about earthquakes?

Dr. Michael Blanpied:  The USGS really has two goals with respect to earthquakes in the country. One is to be able to measure them and very quickly put out information after they occur. Another is, to anticipate what damage may be coming from earthquakes in the future.

One of the key things that the USGS Earthquake Hazards Program produces is an assessment of the earthquake hazards in the United States. This is a map, your Seismic Hazard Assessment Map, and we update it about every five or six years. And what it depicts is the likelihood of strong shaking over the coming decades for the United States.

This is very useful because it goes straight into building codes, for example, that dictate how strong buildings need to be in order to be safe from earthquakes. And it also gives an indication about what areas of the country are those for which people need to be aware of the hazards and learn about them and be ready so that if earthquakes do happen, that they're safe.

Ray Douglas:  Mike, thanks for talking with us and for all of the great work you and the USGS team do to help us understand and predict earthquakes.

Any closing thoughts on the earthquakes here, in the US, and those around the world?

Dr. Michael Blanpied:  Each earthquake around the world really brings new lessons home. The earthquake in Haiti taught us the value of knowing about earthquakes. The Haitian people did not know that the earthquakes were hazards there. They did not build with an awareness of an earthquake hazard and therefore, their buildings were not prepared and the folks were not prepared.

Chile taught us a very different lesson. In fact, the opposite lesson of the value of preparation. Chile experienced one of the largest earthquakes in the century. It was a magnitude 8.8 earthquake; it was just huge. However, Chile experiences a lot of earthquakes. The people are aware that earthquakes are hazard and they're prepared for them. The buildings in Chile are built to a modern code akin to that used in the United States. They used modern building techniques and modern structures. 

Now, in the Central US, we don't have very frequent earthquakes. Often, people think of earthquakes as being a West Coast problem and that is an issue because there may not be a lot of impetus felt by folks in Missouri, say, or Tennessee to be making earthquake plans, just in case one happens in the future.

Newscaster 1: Was that an earthquake?

[Start of Audio]

[Earthquake simulated sound - crash of falling debris, car horn, alarms -  audio mix]

Dr. Michael Blanpied: The thing about earthquake and earthquake hazards are they're so preventable. If we build good buildings, there's no reason any building should collapse. There's no reason any person should die from an earthquake.

Newscaster 1:  We have some new updates. The US Geological Survey says it was of course 5.4…

Newscaster 2: Seismic activity centered in on the New Madid area. Does it extend...

Ray Douglas:  We've been talking with Dr. Michael Blandpied, Associate Coordinator for the USGS Earthquake Hazards Program.

For more information on earthquakes, visit us on the Web at earthquake.usgs.gov.

Ray Douglas:  CoreCast is a product of the U.S. Department of Interior and the U.S. Geological Survey.

[End of Audio]

Thank you for listening.