It may not be the big one

After the recent low magnitude earthquakes in Arkansas, scientists from The University of Memphis continue to try to determine the seismological future of the New Madrid zone.

The New Madrid zone includes parts of Arkansas, Illinois, Kentucky, Missouri, Mississippi and Tennessee.

Chris Cramer, associate research professor at the Center for Earthquake Research and Information (CERI), said one of the ways to measure the strength of an earthquake is the Richter scale, and each level is 32 times stronger than the one before it.

Cramer said the chance of an earthquake of magnitude 7.0 or greater in the New Madrid zone is about 7 to 10 percent in the next 50 years. The possibility of a magnitude 6.0 or greater quake is about 25 to 40 percent in the next 50 years.

"A magnitude 6.5, depending on where it occurs, could cause moderate damage to older buildings and structures, but a magnitude 7.0 or greater could be felt across seven states and would cause significant damage," Cramer said.

He said the older buildings downtown might see the most damage because they are not reinforced like some of the newer buildings. Water and sewage lines would burst in a major earthquake so residents should be prepared with fresh water. Victims in a quake should be ready to spend three to 10 days without power. People should be prepared with radios and flashlights, Cramer said.

Unlike California which has around 2,000 earthquakes a year, some that are destructive, the New Madrid seismic zone only registers about 200 a year, and rarely experiences earthquakes that cause damage. The five earthquakes in Arkansas last week ranged in magnitude from 2.2 to 2.7 and were probably not felt by anyone in the area.

Gary Patterson, education and outreach director at CERI, said the earthquakes in California can be easily explained because it is in the area where two tectonic plates rub against each other. The tension of these plates builds until the energy causes an earthquake.

"It is like stretching a rubber band, and after a while the tension becomes too much and it breaks," Patterson said.

The New Madrid zone experienced large magnitude earthquakes in 1811 and 1812 that caused large amounts of damage.

The community started to prepare for the possibility of another large quake in the mid-1990s by enforcing building codes to provide a minimum resistance to disasters, Patterson said.

He said the seismic activity in this area is harder to explain and predict because the New Madrid zone is in the middle of the North American plate. The seismic activity in this area is normally a sequence of three quakes with no real explanation as to how they occurred. There is not an accepted theory for why the area is active.

"One theory says the crust is springing back up after being pushed down by a large sheet of ice during the last ice age," Patterson said. "But that is just one idea that cannot be verified because there is something odd about this region."