What are the chances of a major earthquake in Illinois?
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Were you woken up by the 2008 earthquake centered near Mount Carmel, Illinois?
It was a magnitude 5.23 earthquake that struck around 4:37 a.m. on April 18, which happened to be the 102nd anniversary of the 1906 San Francisco. magnitude 7.9 earthquake which killed about 3,000 people.
This year’s Easter Monday anniversary of the Mount Carmel earthquake is a stark reminder of the seismic threat in the Midwest.
Although the Mount Carmel earthquake caused no serious injuries, it raises questions about the chances of ‘the big one’ hitting our area and what you should do if you feel ‘the shaking’.
The Mount Carmel earthquake happened about 150 miles from St. Louis, near the Indiana border. It was in the “Wabash Valley Seismic Zone” which covers southeastern Illinois and southwestern Indiana.
It is near the area better known as the “New Madrid Seismic Zone,” which surrounds a Missouri town of the same name on the banks of the Mississippi River, about 160 miles (264 km) south of St. Louis.
This seismic zone covers the extreme southeast of Missouri, the extreme southern tip of Illinois, the extreme west of Tennessee and Kentucky, and the northeastern part of Arkansas.
This area of New Madrid produced a series of three major earthquakes on December 16, 1811 with an estimated magnitude of 7.6; on January 23, 1812, with a magnitude of 7.5; and on February 7, 1812, with a magnitude of 7.8.
President James Madison in Washington, DC, was awakened by the December 11, 1811 earthquake, and the February 7, 1812 earthquake was probably the most felt in North America, according to the US Geological Survey. The New Madrid earthquakes are believed to be the largest earthquakes east of the Rockies in US history, according to a report by the Missouri State Emergency Management Agency.
At the time of the earthquakes of 1811 and 1812, the population of the Saint-Louis area was approximately 5,700. Today, millions of people live where a repeated event would be felt the hardest.
Bob Bauer, senior geological engineer with the Illinois State Geological Survey, said the Feb. 7, 1812, earthquake caused a surface elevation of about 30 feet at the Mississippi River and disrupted river flow.
“The surface of the ground rose I think about 30 feet and it crossed the Mississippi River and it’s the stories of the river flowing back because the fault crossed there and dammed the Mississippi River “, Bauer said in an interview with the BND.
Here is a series of questions and answers on what you need to know about the seismic threat in the Midwest and the New Madrid Fault:
What is the probability of a repeat of the 1811-1812 earthquakes in New Madrid?
The US Geological Survey reports that there is about a 10% chance of a magnitude 7.5 to 8 earthquake occurring within the next 50 years.
For a magnitude 6 earthquake in New Madrid, there is about a 30% chance within a 50-year window.
What could we expect in the metro-east?
An “intensity” scale that uses Roman numerals measures the impact people would experience during an earthquake.
In a repeat of the 1811-1812 earthquakes, the greater St. Louis area would experience a VII to VIII on an intensity scale of I to X, according to the scale used by the US Geological Survey.
Here are some of the things you can expect in the VII range: “Hard to stand on. Furniture broken. Weak chimneys broken at the roof line. Big bells are ringing. Concrete irrigation ditches are damaged,” according to the US Geological Survey.
Here’s what you can expect in Range VIII: “The steering of motor cars is affected.” Some masonry walls are falling. “Twisting, falling chimneys, factory chimneys, monuments, towers, elevated reservoirs. Frame houses moved on foundations if not bolted… Broken branches of trees. Changes in flow or temperature of sources and sinks.
How many times has the New Madrid Fault experienced major earthquakes like those in 1811-1812?
Prior to the 1811-1812 earthquakes in New Madrid, geologists estimate that there were five other significant earthquakes in the past 5,000 years in this seismic zone.
“It’s happened many times before,” Bauer said.
Occurrences fall within a range of plus or minus 100 to 200 years around a target year, Bauer said. Target years are 1450, 900, 1 AD, 1050 BC and 2350 BC
Can scientists predict when the next one will be?
You may remember when Iben Browning, described by St. Louis Public Radio as a “self-proclaimed climatologist,” predicts a major earthquake around December 3, 1990, on the New Madrid fault. Needless to say, Browning was wrong.
“It can’t be predicted,” Bauer said of a major earthquake. “What we’re talking about is preparing for the worst. Then you are ready for different things that are thrown at you.
Minor earthquakes recorded deep in the ground occur constantly in the New Madrid seismic zone.
The New Madrid seismic zone averages about 200 earthquakes per year with a magnitude of 1 or greater. Tremors of magnitude 2.5 to 3 are large enough to feel and are reported every year, according to a report from the Missouri State Emergency Management Agency.
A map from the US Geological Survey shows that more than 20 earthquakes have been recorded in the New Madrid area over the past month.
Two earthquakes have been recorded in Illinois in the past month. One was a magnitude of 2.3 located north of Edwardsville and southwest of Hamel on March 25. It was about 10 miles below the surface and no one reported feeling it. The other was Wednesday near Springerton, Ill., about 118 miles east of St. Louis.
It was a magnitude of 2.6 and 20 people reported to the US Geological Survey that they felt the quake, which happened about nine miles below the surface. While only 20 people reported this one, the Mount Carmel earthquake in 2008 generated around 40,000 reports on the online “Did you feel it” system monitored by the US Geologicial Survey.
In California, earthquakes occur along the San Andreas Fault, where two of Earth’s tectonic plates collide. In contrast, earthquakes in the New Madrid region occur in “cracks” in the tectonic plate beneath North America, Bauer said.
An earthquake occurs when “rocks forming the earth’s crust slide past each other along a fault,” according to an Illinois hazard mitigation plan. This movement produces vibrations, or seismic waves, which cause jolts or “tremors” that can last from 10 seconds to a few minutes.
The US Geological Survey has produced a 30-second video that shows a computer simulation of ground motion caused by a Magnitude 7.7 earthquake in the seismic zone of New Madrid. Go to earthquake.usgs.gov and type “New Madrid computer simulation” in the search box at the bottom left of the homepage.
What should I do if I feel myself shaking during an earthquake?
Public safety experts urge you to follow this mantra:
Here are more tips from ShakeOut.org, which is sponsored in part by the Federal Emergency Management Agency, the US Geological Survey, and the National Science Foundation:
Drop to your hands and knees where you are and don’t run outside.
▪ This position protects you from being knocked over and reduces your chances of being hit by falling objects.
▪ If you are in a wheelchair or walker, lock the device in place.
“Cover your head and neck with one arm and one hand.
▪ If a sturdy table or desk is nearby, crawl under it for cover.
▪ If there is no shelter nearby, crawl along an interior wall.
▪ Stay on your knees; lean forward to protect vital organs.
Hold on the table or desk until the shaking stops.
▪ “Under cover: hold onto it with one hand; be prepared to move with your shelter if it moves.
▪ No shelter: hold on to head and neck with arms and hands.