New Madrid
Seismic Zone
Reinsurance Services
The New Madrid Seismic Zone lies
within the central Mississippi Valley
of the United States, extending from
northeast Arkansas, through southeast
Missouri, western Tennessee, western
Kentucky to southern Illinois. This
region routinely generates several
small earthquakes a month. The fault
is active, averaging more than 200
measured events per year. Tremors
large enough to be felt (magnitude 2.5
to 3.0) occur annually. About every 18
months, the fault releases a shock of
4.0 or more, capable of local minor
damage. Magnitudes of 5.0 or greater
occur about once per decade, which
are capable of significant damage and
being felt across several states. The
graphic on the lower right shows the
earthquakes that have occurred in this
area since 1973.
Overall, the seismic hazard on the
West Coast is higher than in the New
Madrid Seismic Zone. This is due to
two key factors: (1) overall seismic
activity is more common on the West
Coast, and (2) the frequency of large
and damaging earthquakes is
substantially higher.
The main concern about the New
Madrid Seismic Zone stems from two
key factors: (1) the zone is known to
have produced a number of very large
earthquakes, and (2) the nature of the
ground in the New Madrid region
causes earthquake damage to be
spread over a much larger area than
from comparable earthquakes on the
West Coast.
One of the challenges when discussing the New Madrid Seismic Zone is that while low-level seismic activity is
common, larger earthquakes are relatively rare. Modern scientific measurements for the large historic earthquakes
are not readily available and scientists must make educated estimates about what has happened and what could
happen. Differences in these estimates can lead to confusion about the frequency and severity of earthquake
exposure in the New Madrid Seismic Zone.
Impact Forecasting® is a wholly owned subsidiary of Aon Corporation
1
New Madrid
Seismic Zone
Reinsurance Services
In the early 1800's, the New Madrid Seismic Zone was the site of what are considered to be the largest earthquakes
to have occurred in the continental United States. During the winter of 1811-1812, a series of three earthquakes
estimated at magnitude 8 or larger struck in a period of three months. In the 200 years since the “big three”, there
have been several large earthquakes (magnitude 6 to magnitude 7). The big earthquakes of 1811 and 1812 happened
before the invention of the modern seismograph. Records of the event are based on anecdotal comments about
shaking and damage. Most of the people who recorded what happened were located in the Northeast and the river
valleys. There is little record of what happened in the geographic areas that would one day become Arkansas,
Missouri or other states to the west. Data on what happened away from the American settlements of the time is also
scarce.
Many are familiar with the Northridge earthquake, a
magnitude 6.7 earthquake in California in 1994. One of the
large (not largest) New Madrid earthquakes was of a similar
size, the 1895 magnitude 6.8 earthquake. There are records of
the 1895 earthquake ringing church bells as far away as
Boston. Damage along the Mississippi River and throughout
the Ohio River Valley was extensive. The smaller (still
considerable) 1895 magnitude 6.8 earthquake was a little
better documented than the 1811-1812 events. The United
States Geologic Survey (USGS) had been established, and one
of the department’s early staff was an amateur photographer
(the camera had been invented). A photo of the damage is
shown to the right.
The technology to build hospitals, schools, homes and businesses to better withstand earthquakes has advanced
considerably. Unfortunately, the seismic building standards used in higher hazard areas such as California have not
been used as extensively in the New Madrid Seismic Zone. Estimation of this (relative) vulnerability is another
factor that leads to confusion in understanding New Madrid exposure.
If additional information or assistance is requested, please contact Impact Forecasting by phone at (312) 381-5919,
by email at [email protected], or by the worldwide web at www.impactforecasting.com.
Copyright © by Impact Forecasting®, L.L.C. No claim to original government works. The text and graphics of this publication are provided
for informational purposes only. While Impact Forecasting® has tried to provide accurate and timely information, inadvertent technical
inaccuracies and typographical errors may exist, and Impact Forecasting® does not warrant that the information is accurate, complete or current.
The data presented at this site is intended to convey only general information on current natural perils and must not be used to make life-or-death
decisions or decisions relating to the protection of property, as the data may not be accurate. Please listen to official information sources for
current storm information. This data has no official status and should not be used for emergency response decision-making under any
circumstances.
Impact Forecasting® is a wholly owned subsidiary of Aon Corporation
2