New Madrid Earthquakes
207 YEARS AGO TODAY- Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account.
On the 16th of December, 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. 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, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible.
This is a reminder that today is the 207th anniversary of the New Madrid Seismic Zone Earthquakes of December 16, 1811.
The main shock that occurred at 2:15 AM on December 16, 1811, was a result of slippage along the Cottonwood Grove Fault in northeastern Arkansas. It was followed by at least three large aftershocks with magnitudes that ranged from 6.0 to 7.0 over the course of the next 48 hours. Despite the strength of the tremors, only minor damage to human-made structures was reported: from collapsing chimneys, falling trees, and cracking timbers in houses. Some areas sank, while others were uplifted. Fissures opened in the ground; some were filled with water from the nearby Mississippi River or wetlands, which was later expelled high into the air when the fissures closed. Soil liquefaction caused large sand blows that fouled farmland in Missouri, Tennessee, and Arkansas. On the Mississippi River itself, the shaking calved the soil along riverbanks and caused trees lining the river to fall into the water. Large waves formed on the water that capsized numerous boats and thrust others onto the land.
Since the rocks in the eastern United States have few active faults to interrupt the propagation of seismic waves, ground vibrations from earthquakes generated in the region may travel thousands of miles. Shortly after the earthquake began, ground shaking was felt as far away as Canada in the north and the Gulf Coast in the south. Eyewitness accounts noted that the shaking rang church bells as far away as Boston, Massachusetts, and brought down chimneys in Cincinnati, Ohio, about 360 miles (580 km) away. U.S. Pres. James Madison is said to have felt the seismic waves arriving in Washington, D.C. In 2011 the results of a report prepared by the USGS noted that residents within an area of approximately 232,000 square miles (about 600,000 square km) experienced very strong ground shaking, and people living in an area of roughly 965,000 square miles (about 2,500,000 square km) experienced shaking that was intense enough to frighten them.
The strongest aftershock, a magnitude-7.0 tremor that became known as the “dawn aftershock,” occurred later that day at 7:15 AM. The epicentre of the aftershock is a matter of some debate; some Earth scientists noted that it was located in northeastern Arkansas, whereas others maintained that it was located in northwestern Tennessee near the southern end of the Reelfoot Fault, a large fault running northwest-southeast within the Reelfoot Rift. Eyewitnesses reported that shaking from this temblor was severe, especially in New Bourbon, Missouri, but not as strong as the main shock. Like the main shock, however, seismic waves from this event were also felt in cities along the Eastern Seaboard.
The main shock that occurred at 2:15 AM on December 16, 1811, was a result of slippage along the Cottonwood Grove Fault in northeastern Arkansas. It was followed by at least three large aftershocks with magnitudes that ranged from 6.0 to 7.0 over the course of the next 48 hours. Despite the strength of the tremors, only minor damage to human-made structures was reported: from collapsing chimneys, falling trees, and cracking timbers in houses. Some areas sank, while others were uplifted. Fissures opened in the ground; some were filled with water from the nearby Mississippi River or wetlands, which was later expelled high into the air when the fissures closed. Soil liquefaction caused large sand blows that fouled farmland in Missouri, Tennessee, and Arkansas. On the Mississippi River itself, the shaking calved the soil along riverbanks and caused trees lining the river to fall into the water. Large waves formed on the water that capsized numerous boats and thrust others onto the land.
Since the rocks in the eastern United States have few active faults to interrupt the propagation of seismic waves, ground vibrations from earthquakes generated in the region may travel thousands of miles. Shortly after the earthquake began, ground shaking was felt as far away as Canada in the north and the Gulf Coast in the south. Eyewitness accounts noted that the shaking rang church bells as far away as Boston, Massachusetts, and brought down chimneys in Cincinnati, Ohio, about 360 miles (580 km) away. U.S. Pres. James Madison is said to have felt the seismic waves arriving in Washington, D.C. In 2011 the results of a report prepared by the USGS noted that residents within an area of approximately 232,000 square miles (about 600,000 square km) experienced very strong ground shaking, and people living in an area of roughly 965,000 square miles (about 2,500,000 square km) experienced shaking that was intense enough to frighten them.
The strongest aftershock, a magnitude-7.0 tremor that became known as the “dawn aftershock,” occurred later that day at 7:15 AM. The epicentre of the aftershock is a matter of some debate; some Earth scientists noted that it was located in northeastern Arkansas, whereas others maintained that it was located in northwestern Tennessee near the southern end of the Reelfoot Fault, a large fault running northwest-southeast within the Reelfoot Rift. Eyewitnesses reported that shaking from this temblor was severe, especially in New Bourbon, Missouri, but not as strong as the main shock. Like the main shock, however, seismic waves from this event were also felt in cities along the Eastern Seaboard.
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