Friday, July 31, 2015

USGS: New Madrid Simulation Shows Risks For Memphis & Little Rock


Seismic Hazard Map – Credit USGS




In 2011 – during the bicentennial of the four great New Madrid earthquakes of 1811-12 – FEMA and other federal agencies mounted the largest National Level Exercise (NLE) to that date, revolving around a catastrophic earthquake occurring in the New Madrid Seismic Zone (NMSZ) that would involve eight Central U.S. States: Alabama, Arkansas, Kentucky, Illinois, Indiana, Mississippi, Missouri, and Tennessee spread across 4 FEMA regions (IV, V, VI, and VII).


While sparsely populated 200 years ago during the last big seismic event, a similar quake today would endanger millions of people living in the central United States, and likely cause severe economic and social disruption across an even wider area of the nation.


This National Level Exercise tested initial incident response along with disaster recovery plans. According to FEMA’s NLE fact sheet, the exercise was designed to validate the following capabilities:

  • Communications
  • Critical resource logistics and distribution
  • Mass care (sheltering, feeding and related services)
  • Medical surge
  • Citizen evacuation and shelter-in-place
  • Emergency public information and warning
  • Emergency operations center (EOC) management
  • Long term recovery


While large quakes in the middle of the country are rare, the USGS, in Earthquake Hazard in the New Madrid Seismic Zone Remains a Concern, warns:

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.


Complicating matters, earthquakes in the central and eastern part of the nation are generally felt over a much wider area than those on the west coast, due to differences in their underlying bedrock.  In 2012’s USGS: Eastern Earthquakes - Rare But Powerful, we looked at this phenomenon.


The following shake map from the USGS shows the areas reporting shaking from two recent quakes, a 6.0 in Central California, and the recent 5.8 Virginia quake. By an incredibly large margin, the smaller eastern quake was felt over a much bigger area.



All of which serves as prelude to yesterday’s release from the USGS that shows that computer simulations indicate a future New Madrid quake could produce major, prolonged ground shaking in metropolitan areas across several states, including Memphis, TN, Paducah, KY, Evansville, IN, and Little Rock, AR.


New Simulations of 1811-1812 New Madrid Earthquakes Show Strong and Prolonged Ground Shaking in Memphis and Little Rock

Released: 7/30/2015 2:00:00 PM

Computer simulations of earthquake shaking, replicating the quakes that occurred in 1811-1812 in the New Madrid seismic zone (NMSZ), indicate that future large earthquakes there would produce major, prolonged ground shaking. The 1811-1812 events were some of the largest in the United States since its settlement by Europeans, and the NMSZ spans portions of seven states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi.

Scientists from the Universidad Nacional Autónoma de México, the U.S. Geological Survey, San Diego State University, AECOM (formerly URS Corporation), and the University of Memphis simulated a set of 20 hypothetical, yet plausible earthquakes located along two currently active faults in the NMSZ. The hypothetical earthquake scenarios range in magnitude from 7.0 to 7.7, and consider various possible epicenters.

”Based on our simulations, were the 1811-1812 earthquakes to repeat today, more than 8 million people living and working near the New Madrid seismic zone would experience potentially damaging ground shaking at modified Mercalli intensities ranging from VI to VIII,” said Leonardo Ramirez-Guzman, lead author of the paper that appears in the July 30 edition of the Bulletin of the Seismological Society of America.

“Strong ground shaking in the greater Memphis metropolitan area could last from 30 seconds to more than 60 seconds, depending on the magnitude and epicenter of a potential seismic event,” said Ramirez-Guzman, a professor at Universidad Nacional Autónoma de México and former USGS contract scientist.

The simulations also demonstrate the importance of fault rupture directivity (seismic energy focused along the direction of faulting), especially when combined with the wave channeling effects of the Reelfoot rift, a buried, northeast-southwest trending geologic valley in the NMSZ. In particular, future large earthquakes on the approximately 80-mile long NMSZ fault show strong shaking at vibration frequencies that pose a risk for mid-rise to high-rise buildings and tall bridges. This fault is thought to be responsible for the December 16, 1811 magnitude 7-7.7 earthquake. Some of the earthquake simulations showed strong shaking focused to the northeast as far as 100-200 miles away near Paducah, Kentucky and Evansville, Indiana, and to the southwest 150 miles toward Little Rock, Arkansas. An example of this earthquake shaking focusing effect can be seen here.

While it’s not possible to know which direction a fault will rupture once an earthquake starts, knowing that there is an increased chance of strong shaking along these geologically-defined corridors is a valuable aid in better characterizing seismic hazard and minimizing earthquake risk.

Earthquakes pose a significant risk to nearly 150 million Americans. The USGS and its partners in the multi-agency National Earthquake Hazard Reduction Program are working to improve earthquake monitoring and reporting capabilities via the USGS Advanced National Seismic System (ANSS). More information about ANSS can be found on the ANSS website.

caption below

Peak ground-motion variability for a magnitude 7.7 earthquake. Warmer colors indicate stronger ground motions. The stronger ground motions are extended further northeast and southwest caused by the channeling effect of the Reelfoot rift (RFR) The fault is displayed as a thick black continuous straight line, with the epicenter indicated by the triangle. (high resolution image 1.3 MB)


From my 10 years of living in the mostly rural Bootheel of Missouri, I know that most local residents are aware of the seismic history of the region, and are – in general – a fairly resilient lot.  As farmers and ranchers, they tend to be a bit more self sufficient than those who live in surrounding cities.

But as mentioned above, a rupture of the New Madrid fault could have serious effects on cities 100-200 miles away.


Areas where millions of people live and work in structures that were not designed with earthquake safety in mind, and where severe disruptions of essential services (water, power, EMS) – particularly during the winter – could make life extremely difficult.


All of which makes participating in this year’s Great Central U.S. Shakeout, and preparing your home and family for an earthquake, all the more important.  Those who live in other seismically active regions (worldwide) will want to visit for information on your region’s activities.




For more recent blogs on earthquakes, and earthquake preparedness, you may wish to revisit:


OSU: Pragmatic Action - Not Fatalism - In Order To Survive The `Big One’
Shakeout.Org Twitter Chat On Earthquake Preparedness
USGS/OGS Joint Statement On Increased Earthquake Threat To Oklahoma

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