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For most Jacksonville residents, the gentle rocker at 2:18 p.m. Thursday came and went. Those who noticed might have mistaken it for a big truck passing by.
The USGS confirms that a 3.8-magnitude earthquake occurred about 5 miles underground near Rockville, Indiana. Although considered minor – 3.0 is the lowest volume ever recorded – it was powerful enough to be felt. Its strength is usually 4.0 degrees as the vibration becomes noticeable indoors and things start to vibrate.
But the USGS says it has already received reports from as far away as Chicago and the St. Louis area.
In Jacksonville – 254 kilometers from the epicenter – two people reported the event to the federal agency. It is rated III on the modified Mercalli intensity scale, which means it can be “feeled noticeably by people indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing vehicles may shake slightly.”
Someone reported it in Frederick, Schuyler County – 264 kilometers from the epicenter – but it was rated second on the intensity scale, meaning few people likely felt it.
It was even more acute in Raymond. The Montgomery County town, 207 kilometers from Rockville, Indiana, is rated IV on a modified Mercalli density scale, intense enough to wake people up and cause crackling sounds in walls with “a sensation like a heavy truck hitting a building.”
An earthquake in Illinois is rare. USGS officials say the state’s average lifespan is one per year, but only once every 20 years there is one strong enough to cause minor damage. A 3.8-magnitude earthquake was reported in southeastern Illinois in September 2017.
Illinois lies along two fault lines – the New Madrid Seismic Zone and the Wabash Valley Seismic Zone – so the risk is there.
“While some hazards, such as storms, hurricanes, and flooding, can be expected to provide advance notice to residents in a hazardous area, others such as earthquakes cannot be predicted,” said Alicia Tate Nadeau, director of the Illinois Emergency Management Agency. Earthquakes can happen anywhere and at any time, including while you are at work, at home, or on vacation. Creating an environment of education, awareness, and preparedness can save lives.”
The largest earthquake occurred in Illinois at 11:02 am on November 9, 1968, with a magnitude of 5.4 on the Richter scale. The epicenter was in Hamilton County, about 190 kilometers east of St. Louis, and was felt by people across parts of 23 states, according to historical records. There was widespread damage as far north as Chicago.
The Illinois Emergency Management Agency says that most injuries and deaths from earthquakes are caused by debris and objects falling on people. Each fall participates in International ShakeOut Day on the third Thursday in October so people can practice learning how to “fall, cover, and wait” in the event of an earthquake – falling to the ground, sheltering under sturdy furniture, and holding on until the shaking ends.
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