1811–12 New Madrid earthquakes
The 1811–12 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial earthquake of moment magnitude 7.5–7.9 on December 16, 1811, followed by a moment magnitude 7.4 aftershock on the same day. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. They, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within the US state of Missouri.
There are estimates that these stable continental region earthquakes were felt strongly over roughly 130,000 square kilometers (50,000 sq mi), and moderately across nearly 3 million square kilometers (1 million square miles). The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 km2 (6,200 sq mi).
Susan Hough, a seismologist of the United States Geological Survey (USGS), has estimated the earthquakes' magnitudes as around magnitude 7.
There were many more aftershocks, including one magnitude 7 aftershock to the December 16, 1811 earthquake which occurred at 0600 UTC (12:00 a.m.) on December 17, 1811, and one magnitude 7 aftershock to the February 7, 1812 earthquake which occurred on the same day at 0440 UTC (10:40 p.m.).
John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.
After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
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