1811-1812 New Madrid Earthquakes
200 years ago, on December 16, 1811, many throughout the populated areas of the U.S. were awakened by violent shaking at about 2:15 am followed by another violent shaking about 8 am. This was the first of the three New Madrid faults to release energy estimated in the mid-7 magnitude. These 3 faults run from about Cairo, Illinois down to Marked Tree, Arkansas. Accounts of these earthquakes and aftershocks were made for months by Mr. Jared Brooks located in Louisville, Kentucky, 240 miles from the epicenters which were near New Madrid, Missouri. Parts of his descriptions for Dec. 16th follow:
2:15 am - “…commencing with about half the strength to which it gradually increased in about one minute; held at tremendous about one minute, then gradually subsided; whole duration, from 3 ½ to 4 minutes”
7:20 am - “…sudden; violent about 1 minute, then moderated through the 2nd and 3rd minutes to slight tremor; this followed by small and placid motion of about 10 minutes; then severe, stood at that 10 seconds; gradually subsided, but not to perfect rest; six considerable shocks are felt during the succeeding 30 minutes; then became constant, and strengthened at a dreadful rate to tremendous, so as to threaten the town with total destruction; duration of greatest violence 1 ½ minutes; it is doubtful if the earth is at rest from these troubles 10 minutes during the day and succeeding night.”
In the following 5 weeks, 602 aftershocks were felt in Louisville, an average of 1 shake every 1½ hours with 6 of these estimated with magnitudes in the 6s. The second New Madrid fault released in the mid 7s magnitude on January 23, 1812 with 300 aftershocks in the following 2 weeks and the third New Madrid fault released the greatest amount of energy on February 7, 1812 with 970 aftershocks the following 6 weeks.
Researchers find evidence that major earthquakes occurred on the New Madrid faults not only 200 years ago, but also about 550, 1100 and 1700 years ago and there is some evidence for an even older event 2600 years ago. Historic damaging (low- to mid-6 magnitude) events have also occurred in the New Madrid seismic zone (NMSZ) in 1843 at the southern end and 1895 at the northern end just west of Cairo. There are about 100 to 200 earthquakes per year in the NMSZ that are mostly only detected by seismographic recording stations in the area.
Resources and Links
Eyewitness accounts can be found at: www.ceri.memphis.edu.
A U.S. Geological Survey poster showing 1811-1812 first-hand accounts in various cities: pubs.usgs.gov/gip/118/pdf/GIP118.pdf.
Earthquake Hazard in New Madrid Seismic Zone Remains a Concern: pubs.usgs.gov/fs/2009/3071/pdf/FS09-3071.pdf.
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