April 27, 2008
Do Recent Earthquakes Portend A Greater Disaster?
from USGS
Recent earthquakes in Nevada and Indiana upset folks accustomed to terra firma.
The relatively minor Nevada tremor on Friday, near Verdi-Mogul, was rated 4.7 on the 10-point Richter Scale. No one was injured.
The April 18 quake -- centered near Evansville, Indiana -- rattled dishes, dislodged a few bricks, collapsed a front porch and sent tender-footed cats scurrying under beds.
There were no injuries to man or beast. However, seismologists rated it 5.2 on the Richter Scale.
Largest U.S. Quake
Largest U.S. quake recorded was 9.2 at Anchorage, Alaska, on Good Friday 1964. It liquefied the clay ground, toppled buildings and caused 131 deaths.
However the horrendous San Francisco quake in 1906 leveled the city which caught fire and killed an estimated 3,000 people.
Those of us who hear bumps in the night, worry that Evansville is an outskirt of the New Madrid Fault Line along the Mississippi River.
Mammoth earthquakes along the New Madrid line -- in the Winter of 1811-12 – heavily damaged the small towns of St. Louis and Memphis.
Eyewitness
New Madrid earthquake woodcut (adapted from Wikipedia)
A vivid, eyewitness account of the New Madrid quakes was deposed by Eliza Bryan, a local resident. Her memoir is on file at the State Historical Society of Missouri.
“On December 16, 1811, we were visited by a violent shock of an earthquake. It was accompanied by a very awful noise resembling loud but distant thunder -- but more hoarse and vibration.
“This was followed in a few minutes by the complete saturation of the atmosphere with sulphurous vapor, causing total darkness.
“Truly horrible were screams of the affrighted inhabitants running to and fro – not knowing where to go, or what to do.
“Cries of the fowls and beasts of every species – the cracking of trees falling – and the roaring of the Mississippi which was retrograde for a few minutes.
“Inhabitants fled in every direction, supposing that there was less danger at a distance than near the river.
“There were several, lighter shocks daily until the 23rd of January l812. Then, one occurred as violent as the severest of the former ones.
“From this time, until the 4th of February, the earth was in continual agitation – visibly waving as a gentle sea.
“On Feb 7, about 4 a.m., a concussion took place so much more violent than those that had proceeded it that it was denominated ‘The hard shock.’
“The awful darkness of the atmosphere saturated with sulphurous vapor -- and violence of the tempestuous thundering noise -- formed a scene beyond imagination.
“At first, the Mississippi seemed to recede from its banks – its waters gathering up like a mountain. For a moment, many boats on their way to New Orleans were left on bare sand. The poor sailors made their escape from them.
“The river then rose 15 to 20 feet perpendicularly, and expanded. The banks overflowed with the retrograde current. Boats that had been left on sand now were torn from their moorings.
“The river --falling as rapidly as it had risen -- took with it whole groves of cottonwood trees. A great many fish were left on the banks.
“In all the hard shocks, the earth was horribly torn to pieces. Hundreds of acres were covered over by sand that issued from the fissures. In some places, there was a substance resembling coal.
“Lately, it has been discovered that a lake (Reelfoot) was formed on the opposite side of the Mississippi in Indian country (west Tennessee.) It is upward of 100 miles in length, one to six miles wide, and depths of 10 to 50 feet.
“For eighteen months, we were constrained by the fear that our houses would fall from the continuing shocks, and so lived in little, light camps. Some people fled, never to return, but most drifted back.”
Geological Notes
from USGS
The U.S. Geological Survey rates the three main quakes in the central Mississippi valley in the winter of 1811-12 as: “The most powerful in U.S. history!”
There were no seismographs back then. However, the extent of land changes indicate three, closely related quakes – with magnitudes of 8 or more on the Richter scale.
USGS says: "Earthquakes in the central United States affect much larger areas than earthquakes of similar magnitude in the western U.S."
New Madrid in 1811 consisted of 400 log cabins. St. Louis and Memphis were small towns. "Should a category-8 quake occur there today, those cities would be mostly destroyed and thousands of people killed," says USGS.
Questions To Ponder
Which is worst – hurricanes, tornadoes, floods, forest fires, mud slides, volcanoes or earthquakes?
adapted from USGS
By Lindsey Wilger Williams, retired newspaper publisher and syndicated columnist
