U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3071

August 2009

Earthquake Hazard in the New Madrid Seismic Zone Remains a Concern

Printed on recycled paper

There is broad agreement in the scientific community that 

a continuing concern exists for a major destructive earthquake 

in the New Madrid seismic zone. Many structures in Memphis, 

Tenn., St. Louis, Mo., and other communities in the central 

Mississippi River Valley region are vulnerable and at risk from 

severe ground shaking. This assessment is based on decades of 

research on New Madrid earthquakes and related phenomena by 

dozens of Federal, university, State, and consulting earth 

scientists.

Considerable interest has developed recently from 

media reports that the New Madrid seismic zone may be 

shutting down. These reports stem from published research 

using global positioning system (GPS) instruments with 

results of geodetic measurements of strain in the Earth’s 

crust. Because of a lack of measurable strain at the surface 

in some areas of the seismic zone over the past 14 years, 

arguments have been advanced that there is no buildup of 

stress at depth within the New Madrid seismic zone and 

that the zone may no longer pose a significant hazard. 

As part of the consensus-building process used 

to develop the national seismic hazard maps, the U.S. 

Geological Survey (USGS) convened a workshop 

of experts in 2006 to evaluate the latest findings in 

earthquake hazards in the Eastern United States. These 

experts considered the GPS data from New Madrid 

available at that time that also showed little to no ground 

movement at the surface. The experts did not find the GPS 

data to be a convincing reason to lower the assessment of 

earthquake hazard in the New Madrid region, especially 

in light of the many other types of data that are used to 

construct the hazard assessment, several of which are 

described here.

The Geological Record

There are historical accounts of major earthquakes 

in the New Madrid region during 1811–12. The geologic 

record of pre-1811 earthquakes also reveals that the New 

Madrid seismic zone has repeatedly produced sequences 

of major earthquakes, including several of magnitude 7 

to 8, over the past 4,500 years. These prehistoric earthquakes 

caused severe and widespread ground failures in the New 

Madrid region, much like those caused by the 1811–12 earthquake sequence. The key evidence for large earthquakes that 

occurred in the past are sand blows that formed when underground sand and water erupted to the surface as a result of violent shaking. Numerous large sand blows over a wide area were 

created by strong ground shaking during the 1811–12 earthquakes. Similarly large, widespread, and abundant prehistoric 

sand blows were produced over the same area during ground 

shaking from previous clusters of large earthquakes around A.D. 

1450, A.D. 900, and 2350 B.C. The sizes and areal distribution 

of the prehistoric sand blows indicate that the older earthquakes 

were similar in location and magnitude to the 1811–12 shocks.

Memphis

Nashville

St. Louis

Indianapolis

MISSOURI

ARKANSAS

MISSISSIPPI

ALABAMA

TENNESSEE

KENTUCKY

ILLINOIS

INDIANA

Little Rock

Evansville

Springfield

Huntsville

Columbia

Birmingham

Florence

Jackson

Paducah

Louisville

Bloomington

Peoria

Decatur

Jonesboro

Springfield

Pine Bluff

Owensboro

Danville

Terre Haute

Mount Vernon

Poplar Bluff

Cape Girardeau

Hot Springs

Quincy

Ottumwa

IOWA

LOUISIANA

Hopkinsville

Bowling Green

1976

1843

1811

1811

1865

1812

1812

1991

1903

1917

1838

1891

1968

2008

1987

1990

1895

1909

1916

New Madrid

seismic zone 

93°W

41°N

40°N

39°N

38°N

37°N

36°N

35°N

34°N

33°N

92°W 91°W 90°W 89°W 88°W 87°W 86°W

55

55

Topographic map showing earthquakes greater than 

magnitude 2.5 (circles) of the central United States. Red circles 

are earthquakes that occurred after 1972 (U.S. Geological 

Survey Preliminary Determination of Epicenters (PDE) catalog). 

Blue circles are earthquakes that occurred before 1973 

(USGS PDE and historical catalog). Larger earthquakes are 

represented by larger circles. Yellow patches show urban 

areas with populations greater than 10,000.
Continuing Seismic Activity

The New Madrid seismic zone is a source of continuing 

small and moderate earthquakes, which attest to the high stress 

in the region and indicate that the processes that produced 

the large earthquakes over the previous 4,500 years, are still 

operating. It is the most seismically active area of the United 

States east of the Rockies. There is no sign that the rate of 

these smaller earthquakes is decreasing with time, as would be 

expected if they were aftershocks of the 1811–12 earthquakes.

GPS Measurements in the New Madrid Seismic Zone

It has been known for several years that GPS measurements made since about 1996 do not show significant deformation across part of the New Madrid seismic zone. The new 

results reported on recently are not substantially different 

from those derived from previous GPS data. These short-term 

observations, though important, must be tempered by the 

context of tectonic processes developed over many thousands 

to millions of years. Such long-term processes are unlikely to 

switch off in a few decades with an accompanying decrease in 

the earthquake hazard. The New Madrid region is located in the 

middle of the vast North American tectonic plate. In contrast to 

plate boundary settings like the coasts of California or Alaska 

where continuous deformation can be measured at the surface, 

some models predict that little deformation will occur during 

the period between large earthquakes in seismic areas within a 

plate.

The USGS has carried out an extensive consensus-building 

process in the development and updating of the national 

seismic hazard maps. These maps are the basis for the seismic 

provisions in the model-building codes adopted in almost 

all of the United States. Many workshops were conducted 

involving hundreds of scientists and engineers, and a thorough 

peer review process was undertaken in the development of the 

seismic hazard maps. Scientists at some workshops evaluated 

the New Madrid GPS results of the past 12 years and debated 

their meaning. They also considered the clear geologic 

evidence of large earthquakes occurring over the past 4,500 

years and the continuing moderate earthquakes in the area. 

It was the consensus of this broad group of scientists that (1) 

the evidence indicates that we can expect large earthquakes 

similar to the 1811–12 earthquakes to occur in the future with 

an average recurrence time of 500 years and that (2) magnitude 

6 earthquakes, which can also cause serious damage, can be 

expected more frequently than the large 1811–12 shocks.

Based on this history of past earthquakes, the USGS 

estimates the chance of having an earthquake similar to one 

of the 1811–12 sequence in the next 50 years is about 7 to 

10 percent, and the chance of having a magnitude 6 or larger 

earthquake in 50 years is 25 to 40 percent.

Likely Impacts from Future Large Earthquakes

Earthquake hazards involve more than just strong ground 

shaking from passing seismic waves. The 1811–12 earthquakes 

caused many types of ground failures including landslides along 

the Mississippi River bluffs from Mississippi to Kentucky. 

Ground failures also included lateral spreading and ground 

subsidence by soil liquefaction across the Mississippi River 

flood plain and along tributaries to the Mississippi River over 

at least 15,000 square kilometers. Today, a repeat event could 

be expected to produce similar effects in northeastern Arkansas, 

southeastern Missouri, western Tennessee and Kentucky, 

and southern Illinois. Roadways in the Mississippi Valley of 

Arkansas and Missouri (such as Interstate 55) could become 

impassable because of bridge failures and fissuring of road 

surfaces. Venting of large quantities of water, sand, and mud as 

a result of liquefaction could flood fields and roads and disrupt 

agriculture for weeks to months. Flooding of farmland, where 

agricultural chemicals are stored onsite, could contaminate 

rivers and streams. Failure of levees, especially during high 

water, would contribute to flooding, and failures of riverbanks 

could make the Mississippi River and its tributaries difficult to 

navigate for many weeks.

The City of Memphis and the surrounding metropolitan area of more than one million people would be severely 

impacted. Memphis has an aging infrastructure, and many of 

its large buildings, including unreinforced schools and fire and 

police stations, would be particularly vulnerable when subjected 

to severe ground shaking. Relatively few buildings were built 

using building codes that have provisions for seismic-resistant 

design. Soil liquefaction and related ground failures are likely 

to occur in downtown Memphis along the Mississippi River 

and along the Wolf River that passes through Memphis. The 

older highways and railroad bridges that cross the Mississippi 

River, as well as older overpasses, would likely be damaged or 

collapse in the event of a major New Madrid earthquake. Some 

of the bridges and pipelines crossing the Wolf River might be 

damaged or destroyed. Although Memphis is likely to be the 

focus of major damage in the region, St. Louis, Mo., Little 

Rock, Ark., and many small and medium-sized cities would also 

sustain damage.

Continuing Preparedness Needed

The geologic record of repeated large earthquakes, the 

historical accounts of the 1811–12 large earthquakes, and 

the continuing earthquake activity in the area are compelling 

evidence that the New Madrid region has high earthquake 

hazard. The preponderance of evidence leads us to conclude that 

earthquakes can be expected in the future as frequently and as 

severely as in the past 4,500 years. Such high hazard requires 

prudent measures such as adequate building codes to protect 

public safety and ensure the social and economic resilience of 

the region to future earthquakes.

For more information contact:

Robert A. Williams

U.S. Geological Survey

Denver Federal Center

Mail Stop 966, Box 25046

Denver, CO 80225

Email: rawilliams@usgs.gov