Earthquake%20Hazards%20Along%20the%20New%20Madrid%20Fault:%20Using%20Science%20to%20Distinguish%20Fact%20from%20Fiction

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Earthquake Hazards Along the New Madrid Fault
Using Science to Distinguish Fact from
Fiction NSTA, St. Louis 2007 Michael Wysession,
Professor of Geophysics Department of Earth and
Planetary Sciences Washington University, St.
Louis, Missouri
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Acknowledgments Prof. Seth Stein, Northwestern
University Prof. Susan Hough, CalTech National
Science Foundation Incorporated Research
Institutions for Seismology Seismological Society
for America U.S. Geological Survey
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What is it? The NMFZ (New Madrid Fault Zone) is
a region of elevated seismicity at the
intersection of Missouri, Arkansas, Tennessee,
Kentucky, and Illinois
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Why is it there? The NMFZ is associated with the
Reelfoot Rift a failed rift zone that was
active 750 million years ago.
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The Reelfoot Rift is a region of lower elevation
(which is why the Mississippi River flows down
through it!).


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Continents rift apart to make new oceans
Ex/ Continent rifts
Ex/ New ocean
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The Reelfoot Rift began to open when the
supercontinent Rodinia split up about 750 million
years ago, but then stopped called a failed
rift
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What happened in 1811-1812? A swarm of
earthquakes occurred. The largest were magnitude
7.0, 7.2, and 7.4
12/16/1811 M7.2 1/23/1812 M7.0 2/07/1812
M7.4
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Magnitudes were determined by measuring accounts
of intensity of shaking (Mercalli Intensity
Scale) in historical records and comparing them
to magnitudes and recorded intensities for modern
earthquakes Hough et al., 20000
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A Magnitude 8 (M8) earthquake is much bigger than
a M7 earthquake Roughly 10x greater
displacements Roughly 30x more energy released
M 6.9
M 7.8
FAULT LENGTH
FAULT WIDTH
the big one
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There were no seismometers in 1812, so original
sources (accounts) provide the most direct
evidence to constrain the magnitude and location
of earthquakes, but must be considered in their
historic context.
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NEW MADRID, MISSOURI December 16, 1811
"About 200 this morning we were awakened by a
most tremendous noise, while the house danced
about and seemed as if it would fall on our
heads. I cried out it was an Earthquake, and for
the family to leave the house which we found
very difficult to do, owing to its rolling and
jostling about. "At half past 6 o'clock there
was another shock, extremely violent - the
agitation of the earth was so great that it was
with much difficulty I kept my balance - the
motion of the earth was about twelve inches to
and fro. The earth seemed convulsed - the
houses shook very much - chimneys falling in
every direction. The loud hoarse roaring which
attended the earthquake, together with the
cries, screams, and yells of the people, seems
still ringing in my ears.
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REELFOOT LAKE, TN
"Beginning December 16, 1811, there were violent
earthquakes throughout the winter months.  On
some days the atmosphere was so saturated with
sulfurous vapors as to cause total darkness. 
Trees cracked and fell into the roaring
Mississippi. The waters of the river gathered up
like a mountain, rising 15 to 20 feet, then
receding with such violence that it took whole
groves of cottonwoods which edged its borders. 
Fissures in the earth vomited forth sand and
water, some closing again immediately. 
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REELFOOT LAKE, TN
Feb. 19 We have seen a statement by gentlemen
from New Madrid, that that place is much torn to
pieces by the late Earthquake so it is almost
impossible to get along in any way, but on
horseback. Houses of brick, stone and log are
torn to pieces, and those of frame thrown upon
their sides. The ground for 100 acres has sunk so
low that the tops of the tallest trees can hardly
be seen above the water in other places more
than half the length of the timber is under
water.
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What happened away from New Madrid? Not much
S. Hough
INTENSITY OF SHAKING
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Ground motions are usually more severe near
bodies of water
Abundant modern evidence reveals that shaking
during earthquakes is amplified considerably at
sites along major bodies of water, where soils
and sediments are generally loose, as in the
example shown above.
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Ste. Genevieve, Missouri, along the Mississippi,
was hardly damaged
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The New Madrid Earthquakes also triggered large
earthquakes in Mississippi, Illinois, and Kentucky
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Why were the largest quakes felt as far as the
east coast? Eastern North America is made of old,
cold and stiff lithosphere, with no recent
tectonic activity, and so it carries waves great
distances.
Example
Seismograms from a Texas EQ
Mina, NV
Mina, NV
St. Louis, MO
St. Louis, MO
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What can we expect for the future at New
Madrid? Dont know earthquakes cant (yet?) be
predicted. Educated guesses based upon
paleoseismicity, currently levels of seismicity,
and GPS studies
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Seismicity of NMSZ is 1/30-1/100 of the
California rate, due to difference in motion rates
NEW MADRID SEISMICITY


Mgt5 every 15 yr Mgt6 every 150 yr Mgt7 in
1811-12
There has not been a M6 or greater earthquake in
NMSZ since 1800s, nor a M5 or greater in the past
30 years.
1900-2002
NORTH AMERICA
PACIFIC
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NMSZ FREQUENCY-MAGNITUDE RELATIONSHIP
All seismicity, including total global seismicity
follows this general pattern Example/ Each
year, globally Magnitude Number 8 1-2
7 12 6 120 5 1200 4 12,000
Stein Newman, 2004
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NMSZ FREQUENCY-MAGNITUDE RELATIONSHIP

• For New Madrid, combine instrumental seismology
  with earlier data to explore large earthquake
  recurrence
• Large paleoearthquakes occurred at
• 1450 and 900 AD
• (Magnitudes unknown)
• Gives a M7 every few thousand years.
• Might NEVER get a M8 earthquake

Stein Newman, 2004
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Earthquakes occur in the interior of all plates
Intraplate earthquakes seem to occur in clusters
or swarms, unlike the more consistent
plate-boundary earthquakes
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Basel 1356

Some 30 to 40 medieval castles collapsed in the
hardest hit area. Many more churches and towers
toppled within a 200 kilometer radius of Basel,
as the earthquake reached a Mercalli intensity of
IX to X
Megharoui et al., 2001
Basel 1356 M6.0-6.5
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However, even earthquake recurrence along plate
boundaries is highly variable probabilities hard
to assess

• Mgt7 mean 132 yr s 105 yr
• Estimated probability of next earthquake in 30
  yrs is 7-51
• Random!

Elastic Rebound (Seismic Gap) Theory? NY City
Bear Gap Hypothesis?
Sieh et al., 1989
Random seismicity simulation
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Earthquakes occur where earthquakes
occur Earthquakes occur where seismometers exist
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Earthquakes occur where earthquakes
occur Earthquakes occur where seismometers exist
Almost no seismometers here!!
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Notice all the earthquakes EAST of the NMSZ!
The NMSZ might be finished (for now?). It might
be time for a different failed rift to undergo
some continental creaking.
o Historical o Instrumental
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GPS SITE MOTIONS Vertical show glacial
rebound Horizontal show no pattern
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GPS site motions within their ellipse of
uncertainty - no motion!
DONT SEE MOTION AT NEW MADRID OR ELSEWHERE IN
EASTERN US If you dont bend it, you cant
break it
No significant or coherent intraplate deformation
visible
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GPS CONSTRAINTS ON LARGE EARTHQUAKE MAGNITUDE
RECURRENCE

GPS data show little or no (lt 2 mm/yr)
motion Little - or none -accumulating for future
earthquakes

Newman et al, 1999
Intersection of Paleoseismology and GPS evidence
suggests low M7 earthquakes, but larger events
would have VERY long recurrence times.
GPS
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Humans are naturally drawn to the dramatic and
catastrophic Example Since 9/11, when 3000
Americans perished, 150,000 Americans have died
from guns and 200,000 Americans have died on
highways. We seem comfortable with the 350,000
deaths, but in a panic about the 3000.
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U.S. EARTHQUAKES Infrequent, but occasionally
major, fatalities and damage Moderate (M 6.7)
1994 Northridge earthquake 58 deaths, 20B
damage Challenge find mitigation strategy that
balances cost of safer construction with
benefits, given other possible uses of resources
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Humans are naturally drawn to the dramatic and
catastrophic Example Iben Browning
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Humans are naturally drawn to the dramatic and
catastrophic Example Central U.S. Earthquake
Consortium warning for New Madrid
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Seismologists have predicted a 40-60 chance of
a devastating earthquake in the New Madrid
seismic zone in the next ten years. Those odds
jump to 90 over the next 50 years. The potential
magnitude of a catastrophic New Madrid quake
dictates that we approach the preparedness on a
regional basis"
? Unjustified given geologic evidence
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Are the seismic hazards as great in NMSZ as
California? Of course not.
2 chance of shaking within 50 years seismic
hazard within next 2500 years
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More reasonable assessment
The Global Seismic Hazard Assessment Program
(GSHAP), with the support of the International
Council of Scientific Unions (ICSU), and endorsed
as a demonstration program in the framework of
the United Nations International Decade for
Natural Disaster Reduction (UN/IDNDR).