Despite Lack of Headlines, Louisiana In Earthquake Zone

By Nate Monroe | LSU Student

Ardent LSU football junkies might insist the state's largest earthquake came in October 1988, the night of the infamous "Earthquake Game," when LSU beat the Auburn Tigers 7-6. But Louisiana has a history with the real things that long predates the legendary game and continues to this day.

While Louisiana is not considered a high-risk and hasn't seen seismic activity anywhere near the magnitude experienced recently in Chile or Haiti, there have been a handful of significant earthquakes in the state. Two of the largest fault lines run through Baton Rouge.

A series of devastating earthquakes hit the United States in 1811 and 1812 that centered in the New Madrid seismic zone, named after New Madrid, Mo., and part of the new Louisiana Territory. These quakes were some of the largest ever experienced in this nation, and the effects were felt in northern and southern Louisiana, including New Orleans, according to a 2001 report on earthquakes in Louisiana by the Louisiana Geological Survey

The New Madrid zone remains "the area most likely to produce earthquakes that could affect Louisiana," according to the report. Since 1843, the report cites more than 40 earthquakes felt in or around Louisiana.

Earthquakes have hit a wide geographic range around the state – covering southern, central and northern Louisiana. The largest occurred in Louisiana on Oct. 19, 1930, with the epicenter at Donaldsonville. It measured 4.2 on the Richter scale.

The earthquake was powerful enough to register on a seismograph in Washington , D.C. Donaldsonville, Napoleonville and Gonzales all had reports of significant infrastructure damage to brick chimneys and windows, according to the report. Baton Rouge and New Orleans also felt the quake.

The most recent earthquake in Louisiana occurred on Dec. 20, 2005, according to the United States Geological Survey. The quake had a 3.0 magnitude and reportedly was noticed in Baton Rouge, Hammond and New Orleans.

"The only ones that are known are the ones that are felt," said Richard McCulloh, a geologist with the Louisiana Geological Survey and co-author of the report on earthquakes in Louisiana.

McCulloh said relatively little data exists for Louisiana, and historical record for earthquakes in the state relies heavily on anecdotal accounts found in local newspapers.

The Modified Mercalli Intensity Scale chronicles most of Louisiana's earthquake history. The scale uses reports of shakes felt and damage sustained to assign a rate of intensity and to approximate a quake's epicenter.

"The Modified Mercalli Intensities are based in part on postal questionnaires, in which respondents summarize the effects of shaking in their communities," according to the USGS. "In addition, Modified Mercalli Intensities are based on field study in areas of significant damage, on damage maps produced by emergency response agencies, on reports produced by the earthquake engineering community, and on press reports."

McCulloh said qualitative intensity data is useful but limited to the reliability of human witnesses – an unfavorable comparison to magnitude, a quantitative measure which is recorded on seismographs. "It's a different kind of data."

Despite a definite earthquake history, Louisiana has relatively little seismic activity. The most ideal situation for earthquakes]is a plate boundary situation, notes McCulloh.

Louisiana, part of the Gulf Coast Basin, is not near a plate boundary, but the state does have active fault lines – weaknesses in the Earth's crust where rock on one side of a fracture moves relative to the rock on the other side. Earthquakes tend to occur because of massive slippage at these lines.

Another LGS report, also authored by McCulloh, details two active faults in East Baton Rouge Parish – the Denham Springs-Scotlandville fault and the Baton Rouge fault, which together comprise the Baton Rouge fault system.

The Baton Rouge fault runs right through College Drive, about one block north of Corporate Boulevard, where there is a noticeable rise in the road.

McCulloh said the compelling evidence these faults remain active is damaged found on buildings along the faults – signs the faults reach the surface.

McCulloh said it took longer to recognize active, surface-reaching faults in other parts of south Louisiana because many of the faults run through rural areas, with little infrastructure damage to see.

"The faults that we have in south Louisiana are not viewed as seismic faults," McCulloh said. That's because Louisiana's faults, though active, don't seem to cause earthquakes – at least not detectable ones.

"It's conceivable that if you had super-sensitive seismographs right on top of the [Baton Rouge system] faults, you might find micro earthquakes. "