2007 NSTA: St. Louis, MissouriEarthquake Prediction and Forecasting: A Case Study of the San Andreas and
New Madrid Faults
Sponsored by: IRIS (Incorporated Research Institutions for Seismology)NSF (National Science Foundation)
Presented by:John Taber, IRISMichael Wysession, Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri
For all IRIS NSTA activities
www.iris.edu/joomla
Go to: NSTA 2007
OLD Map of “Seismic Gap” Predictions
Parkfield was in correct place, but very late.
Northridge, Landers, Joshua Tree and Big Bear Earthquakes were not even on this map!!!
“New York City Bear Gap” Hypothesis
In 1985 a 6.0 Parkfield earthquake was predicted with 95% confidence to occur by 1993.
Mean = (1966-1857)/5 = 22 yearsExpected date = 1988
Paleoseismology
M >7 mean = 132 yr = 105 yr Estimated probability in 30 yrs 7-51%
Sieh et al., 1989Extend earthquake history with geologic record
The NMFZ (New Madrid Fault Zone) is a region of elevated seismicity at the intersection of Missouri, Arkansas, Tennessee, Kentucky, and Illinois
The NMFZ is associated with the Reelfoot Rift – a failed rift zone that was active 750 million years ago, as the supercontinent Rodinia began to break up.
The Reelfoot Rift is a region of lower elevation (which is why the Mississippi River flows down through it!).
In 1811-1812, swarm of earthquakes occurred. The largest were:
12/16/1811: M7.2 1/23/1812: M7.0 2/07/1812: M7.4
[Hough et al., 2000]
“the big one”
FA
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T L
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GT
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FAULT WIDTH
A Magnitude 8 (M8) earthquake is much bigger than a M7 earthquake:
Roughly 10x greater displacements
Roughly 30x more energy released
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
?
“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
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
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).
More reasonable assessment, based upon actual seismicity
Earthquakes occur where earthquakes occur
Earthquakes occur where seismometers exist
Almost no seismometers!!
o Historical o Instrumental
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.
DON’T SEE MOTION AT NEW MADRID OR ELSEWHERE IN EASTERN US:
If you don’t bend it, you can’t break it
GPS site motions within their ellipse of uncertainty - no
motion!
No significant or coherent intraplate deformation visible
GPS data show little or no (< 2 mm/yr)
motion
Little - or none -accumulating for
future earthquakes
GPS CONSTRAINTS ON LARGE EARTHQUAKE MAGNITUDE & RECURRENCE
GPS
Newman et al, 1999
Intersection of Paleoseismology and GPS evidence suggests low M7 earthquakes, but larger events would have VERY long recurrence times.