Earthquake Program Overview
Over the years, the Missouri state emergency management agency (SEMA)
has made a dedicated effort to protect the lives and property of all Missourians
when major disasters threaten public safety. SEMA responds to two
types of disasters - natural and manmade. Natural disasters are
major snow and/or ice storms, floods, tornadoes and/or severe weather,
as well as the threat of a serious earthquake along Missouri's New Madrid
fault. Manmade disasters, also known as technological emergencies, may
include hazardous material incidents, nuclear power plant accidents
and other radiological hazards, as well as homeland security events in
the new world environment.
One of SEMA’s key roles is to maintain
the State Emergency Operations Plan (SEOP) that is followed by the Missouri
state government departments and agencies when the use of state
resources is required. Following the procedures outlined in the SEOP,
SEMA coordinates the state’s disaster response for all types of
large-scale emergencies. To better prepare for meeting the challenges
associated with disasters, SEMA has developed and implemented a number
of programs that are designed to mitigate damages, enhance
preparedness, improve response operations and aid the recovery
process.
A major earthquake centered in the New Madrid seismic zone
potentially is one of the most serious natural hazard threats facing
the state of Missouri. Experts mostly agree that it is not a matter of
if a significant earthquake occurring, but rather it is a matter of
how soon one will happen. SEMA has developed a multifaceted earthquake
program designed to carry out earthquake awareness and preparedness
programs; Work with partners to promote earthquake loss-reduction
plans, practices and policies that encourage earthquake mitigation;
And develop better response and recovery capabilities through
participation in earthquake training and exercises.
About the New Madrid
Fault
The
New Madrid Fault System extends 120 miles southward from the area of
Charleston, Missouri, and Cairo, Illinois, through New Madrid and
Caruthersville, following Interstate 55 to Blytheville and on down to
Marked Tree, Arkansas. It crosses five state lines and cuts across the
Mississippi River in three places and the Ohio River in two places.
The fault is active, averaging more than 200 measured events per year
(1.0 or more on the Richter scale), about 20 per month. Tremors large
enough to be felt (2.5 – 3.0 on the Richter scale) are noted
annually. Every 18 months the fault releases a shock of 4.0 or more,
capable of local minor damage. Magnitudes of 5.0 or greater occurring
about once per decade can do significant damage and be felt in several
states.
The highest earthquake risk in the mainland United States outside the
West Coast is along the New Madrid Fault. Damaging tremors are not as
frequent as in California, but when they do occur, the destruction
covers over more than 20 times the area because of underlying geology.
A damaging earthquake in this Area, 6.0, reoccurs about every 80 years
(the last one in 1895). In 2002, the U.S. Geological Survey (USGS)
released new earthquake probabilities for the New Madrid Seismic Zone.
For a magnitude 6.0 or greater earthquake, there now is estimated to
be a 25-40% chance in the next 50 years. The results would be serious
damage to schools and masonry buildings from Memphis to St. Louis.
USGS also estimates a 7% - 10% chance of a 7.5 – 8.0 earthquake in
the next 50 years (equal to the earthquake events of 1811-1812).
A major earthquake in this area - the Great New Madrid Earthquake of
1811-12 was actually a series of over 2000 shocks in five months, some
of 7.6 intensity and five of which were 8.0 or more in magnitude.
Eighteen of these rang church bells on the Eastern seaboard.
The very land itself was destroyed in the Missouri Bootheel, making it
unfit even for farming for many years. It was the largest burst of
seismic energy east of the Rocky Mountains in the history of the U.S.
and was several times larger than the San Francisco quake of 1906.
When will another Great Earthquake happen the size of those in
1811-12?
Several lines of research suggest that the catastrophic
upheavals like those in 1811-12 visit the New Madrid region every
500-600 years. Hence, emergency planners, engineers, and seismologists
do not expect a repeat of the intensity of the 1811-12 series for at
least 100 years or more. However, even though the chance is remote,
experts estimate the chances for a repeat earthquake of similar
magnitude to the 1811-1812 New Madrid earthquakes have changed from
the1985 estimates of 2.7 – 4.0% probability in 50 years to a 7 - 10%
probability. This is a result of new evidence of shorter recurrence
intervals identified from pre-historical events. Earthquake
probabilities for known active faults always increase with time,
because stresses within the earth slowly and inexorably mount, year by
year, until the rocks can take no more, and sudden rupture becomes
inevitable.
Our Greatest Concerns are the 6.0-7.6 Sized Events, which do have
significant probabilities in the near future.
Damaging earthquakes of this magnitude are very likely within
the lifetimes of our children.
What Can Be Done to Protect Ourselves?
Education, planning, proper building construction, and
preparedness are proven means to minimize earthquake losses, deaths,
and injuries. In recent memory, San Francisco and Armenia both
experienced 6.0-7.1 magnitude quakes. San Francisco was prepared;
Armenia was not. San Francisco suffered 67 deaths and less than $7
billion in property losses.
Armenia had over 25,000 deaths and lost more than $20 billion.
More recently, Alaska underwent a 7.9 earthquake. Losses were
minimized in this event because the epicenter was in a remote
location. Missouri and the Midwest are more prepared than Armenia, but
only partly as prepared as San Francisco, and the epicenter is not
likely to be in a totally isolated area.
What is the Richter Scale?
The Richter scale of earthquake magnitude is a measure of the
energy released at the source of an earthquake deep within the earth.
It is determined by measuring the amplitudes of ground motion
on seismograms.
An earthquake has a fixed amount of energy and only one Richter
magnitude.
How Much Increase in Energy Does Each Unit of the Richter Scale
Represent?
It is incorrect to say that each unit of the Richter scale
corresponds to a tenfold increase in energy.
Each unit, say from 5.2 to 6.2, actually represents 31.6 times
difference in energy release.
Every two units represent 1,000 times more energy, and every
two-tenths of a unit represents double the energy.
The New Madrid Fault is a complex zone of seismically active fractures
in bedrock buried several thousand feet beneath river sands and mud.
An earthquake’s severity is greatest at its focal point, known as
the epicenter, but lessens as the distance from the epicenter
increases. The hachured areas on the map above show possible damage
levels of a 7.6 earthquake event. The darkest area on the map portrays
an epicenter, potentially the area of greatest damage.
If a Fault Has Lots of Little Earthquakes, Will Larger Ones Be
Prevented?
The answer is, “No”.
A magnitude 6.0 (which is damaging) is 1,000 times more energy
than a 4.0 (which is not damaging).
An 8.0 (which is devastating) is 1,000 times larger than a 6.0.
In other words, a fault would have to have 1,000 4.0 events to
prevent the occurrence of a single 6.0, or a million 4.0 events (1,000
times 1,000) to prevent a single 8.0.
We Have a Choice.
While we still have time, we can get ready and cut our losses,
or we can do little or nothing and be caught unprepared.
We cannot prevent the coming of an earthquake – it will
happen – but we can prevent it from being a major disaster.
Projected
Earthquake Intensities Map (downloadable in
.pdf format)
