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The Great Midwest Earthquake of 1811
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Transcript
Following Quakes
The Initial Quakes
Visual representation of the way that seismic waves travel
January 23, 1812 (9 am)
- Magnitude: 7.0–7.8
- Epicenter in the Missouri Bootheel
- Area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks
- This earthquake was attributed to a rupture on the New Madrid North Fault. which in turn put strain on the Reelfoot Fault
February 7, 1812 (4:45 am)
- Magnitude: 7.4–8.0
- Epicenter near New Madrid, Missouri
- New Madrid was destroyed
- In St. Louis, Missouri, many houses were severely damaged and chimneys were toppled
- This shock was attributed to Reelfoot Fault
Visual representation of the area that was most affected by the quakes
Cause of the Quakes
December 16, 1811 (2:15 am)
- Magnitude: 7.2-8.1
- Epicenter in northeast Arkansas
- Caused only slight damage to man-made structures (low population)
- The future location of Memphis, Tennessee experienced level IX shaking on the Mercalli intensity scale
December 16, 1811 (8:15 am)
- Magnitude 7.2–8.1
- Epicenter in northeast Arkansas
- This shock followed the first earthquake by six hours and was similar in intensity
- About 200 million years ago, rifting took place along the east coast of North America as the Atlantic Ocean began to open, resulting in the continent being stretched, and the Reelfoot Rift being pulled apart.
- Plutons (deep reservoirs of magma) formed along the rift, as molten rock moved upward along the ancient faults and then cooled before reaching the surface.
- Once again the rifting ceased, the ocean advanced over the area and receded; this time the sands, clays and gravels it deposited were not buried deeply enough, or long enough to become rock.
- At Memphis, this material is approximately 3200 feet thick and covers the terrain from Little Rock, AR to the Tennessee River.
A map comparing two 7.3 earthquakes in CA and from the New Madrid Fault
“The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling...formed a scene truly horrible,” wrote one resident.
Map of perceived shaking and location of each quake
Things to keep in mind...
- Destruction was much lower due to the low population
- Most people in the area had never before experienced an earthquake
the BIG question
The New Madrid Fault
What would the effect of such an earthquake be on the midwest today?
From the citizens point of view...
- Located on the border of southeastern Missouri
- Has the potential to be just as deadly as the fault in California
Are we prepared?
Graphics
Map of the United States with potential hazard zones for earthquakes
A closer view of the New Madrid fault, showing the intensity of recorded earthquakes
Formation
Dense mantle material was injected into the lower crust, creating a pillow-shaped structure which was heavier than the surrounding rocks. As the upwelling ceased, the entire rift subsided, and filled with sediments eroded from its flanks.
"[T]he nation’s attention is turned to the likely fate of its great Eastern cities. It shouldn’t be: far greater danger attends the cities of the Midwest, which are perched on a ticking seismic time bomb."
-FEMA, 2011
A more in depth view of the formation of the New Madrid Fault