Re:Current Earthquake Swarms Could Be Precursor to 'Cascadia Subduction

[Guest guest]

Here is some information I found online:

 

Missouri Earthquake History:

 

Most of Missouri's earthquake activity has been

concentrated in the southeast corner of the State,

which lies within the New Madrid seismic zone.

 

The written record of earthquakes in Missouri prior to

the nineteenth century is virtually nonexistent;

however, there is a geologic evidence that the New

Madrid seismic zone has had a long history of

activity. The first written account of an earthquake

in the region was by a French missionary on a voyage

down the Mississippi River. He reported feeling a

distinct tremor on Christmas Day 1699 while camped in

the area of what is now Memphis, Tennessee.

 

Whatever the seismic history of the region may have

been before the first Europeans arrived, after

December 16, 1811, there could be no doubt about the

area's potential to generate severe earthquakes. On

that date, shortly after 2 AM, the first tremor of the

most violent series of earthquakes in the United

States history struck southeast Missouri. In the small

town of New Madrid, about 290 kilometers south of St.

Louis, residents were aroused from their sleep by the

rocking of their cabins, the cracking of timbers, the

clatter of breaking dishes and tumbling furniture, the

rattling of falling chimneys, and the crashing of

falling trees. A terrifying roaring noise was created

as the earthquake waves swept across the ground. Large

fissures suddenly opened and swallowed large

quantities of river and marsh water. As the fissures

closed again, great volumes of mud and sand were

ejected along with the water.

 

The earthquake generated great waves on the

Mississippi River that overwhelmed many boats and

washed others high upon the shore. The waves broke off

thousands of trees and carried them into the river.

High river banks caved in, sand bars gave way, and

entire islands disappeared. The violence of the

earthquake was manifested by great topographic changes

that affected an area of 78,000 to 130,000 square

kilometers.

 

On January 23, 1812, a second major shock, seemingly

more violent than the first, occurred. A third great

earthquake, perhaps the most severe of the series,

struck on February 7, 1812.

 

The three main shocks probably reached intensity XII,

the maximum on the Modified Mercalli scale, although

it is difficult to assign intensities, due to the

scarcity of settlements at the time. Aftershocks

continued to be felt for several years after the

initial tremor. Later evidence indicates that the

epicenter of the first earthquake (December 16, 1811)

was probably in northeast Arkansas. Based on

historical accounts, the epicenter of the February 7,

1812, shocks was probably close to the town of New

Madrid.

 

Although the death toll from the 1811-12 series of

earthquakes has never been tabulated, the loss of life

was very slight. It is likely that if at the time of

the earthquakes the New Madrid area had been as

heavily populated as at present, thousands of persons

would have perished. The main shocks were felt over an

area covering at least 5,180,000 square kilometers.

Chimneys were knocked down in Cincinnati, Ohio, and

bricks were reported to have fallen from chimneys in

Georgia and South Carolina. The first shock was felt

distinctly in Washington, D.C., 700 miles away, and

people there were frightened badly. Other points that

reported feeling this earthquake included New Orleans,

804 kilometers away; Detroit, 965 kilometers away; and

Boston, 1,769 kilometers away.

 

The New Madrid seismic zone has experienced numerous

earthquakes since the 1811-12 series, and at least 35

shocks of intensity V or greater have been recorded in

Missouri since 1811. Numerous earthquakes originating

outside of the State's boundaries have also affected

Missouri. Five of the strongest earthquakes that have

affected Missouri since the 1811-12 series are

described below.

 

On January 4, 1843, a severe earthquake in the New

Madrid area cracked chimneys and walls at Memphis,

Tennessee. One building reportedly collapsed. The

earth sank at some places near New Madrid; there was

an unverified report that two hunters were drowned

during the formation of a lake. The total felt area

included at least 1,036,000 square kilometers.

 

The October 31, 1895, earthquake near Charleston,

Missouri, probably ranks second in intensity to the

1811-12 series. Every building in the commercial area

of Charleston was damaged. Cairo, Illinois, and

Memphis, Tennessee, also suffered significant damage.

Near Charleston, 4 acres of ground sank and a lake was

formed. The shock was felt over all or portions of 23

states and at some places in Canada.

 

A moderate earthquake on April 9, 1917, in the Ste.

Genevieve - St. Marys area was reportedly felt over a

518,000 square kilometer area from Kansas to Ohio and

Wisconsin to Mississippi. In the epicentral area

people ran into the street, windows were broken, and

plaster cracked. A second shock of lesser intensity

was felt in the southern part of the area.

 

The small railroad town of Rodney, Missouri,

experienced a strong earthquake on August 19, 1934. At

nearby Charleston, windows were broken, chimneys were

overthrown or damaged, and articles were knocked from

shelves. Similar effects were observed at Cairo,

Mounds and Mound City, Illinois, and at Wickliff,

Kentucky. The area of destructive intensity included

more than 596 square kilometers.

 

The November 9, 1968, earthquake centered in southern

Illinois was the strongest in the central United

States since 1895. The magnitude 5.5 shock caused

moderate damage to chimneys and walls at Hermann, St.

Charles, St. Louis, and Sikeston, Missouri. The felt

areas include all or portions of 23 states.

 

 

 

 

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