Lecture on the New Madrid Earthquakes of 1811-1812

Overview

• On December 16, 1811, a significant earthquake shook much of the United States.
• The epicenter was near New Madrid, in the Mississippi Valley.
• More than 2,000 earthquakes occurred until February 1812.
• Earthquakes reached magnitudes of 7 to 7.5 or greater.
• It was one of the most powerful earthquake series in U.S. history, occurring in the interior rather than along the West Coast.

Geographic Impact

• The earthquakes were felt nationwide, from Natchez to New York, and as far as a thousand miles from the epicenter.
• Most severe in the Mississippi Valley, affecting New Madrid and surrounding areas.

Eyewitness Accounts

• William Pierce's account: Violent shaking, explosions, spouts of water and sand.
• Eliza Bryan's account: Massive land subsidence, river reversal, destruction of boats.

Geological Aspects

• New Madrid is unusual for earthquakes due to its location away from plate boundaries.
• The Mississippi floodplain is a large sediment-filled area, prone to liquefaction.
• Soil liquefaction causes the ground to behave like quicksand during earthquakes.
• Recorded extensive soil liquefaction, with sandblows reaching 60 meters in diameter.

Historical Context

• New Madrid was part of the newly acquired U.S. territory from the Louisiana Purchase (1804).
• Town and region were severely affected, leading to a disaster relief bill by Congress.

Potential for Future Earthquakes

• Regular seismic activity continues in the New Madrid zone.
• Estimated 25-40% chance of a magnitude 6 or greater quake in the next 50 years.

Challenges in Understanding

• Lack of an agreed model for stress buildup in the region.
• Dense, old crust transfers seismic waves efficiently over large distances.

Implications for Today

• Potential for devastating impacts if similar earthquakes occur now due to population growth and infrastructure developments.
• The region is less prepared for earthquakes compared to places like California.

Conclusion

• Understanding the New Madrid earthquakes is crucial for preparedness and hazard mitigation.
• Future research needed to better predict and manage earthquake risks in the region.