A magnitude 3.5 earthquake struck southern Illinois in the early hours of Tuesday morning, according to the U.S. Geological Survey (USGS), a tremor felt in neighboring St. Louis, Missouri.
The epicenter was located around 2.5 miles east of Ohlman, Illinois, and the quake had a depth of around 5.5 miles, the USGS said. More than 1,000 people reported feeling the tremor to the USGS.
As well as St. Louis, both sides of the Illinois-Missouri border, the quake was felt strongly in Springfield, Decatur, Effingham, and Greenville.
“This large region borders the much more seismically active New Madrid seismic zone on the seismic zone’s north and west,” says the USGS.
“The Illinois basin-Ozark dome region covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis.
“Moderately frequent earthquakes occur at irregular intervals throughout the region.”
These earthquakes in the central and eastern U.S. are “less frequent than in the western U.S.” but are “typically felt over a much broader region,” the USGS says.
The largest earthquake in the region struck in 1968, registering a magnitude of 5.4 and damaging areas of southern Illinois.
Earthquakes of a damaging scale occur in the region every one to two decades, but smaller tremors happen a couple of times a year.
California Earthquake Sparks Emergency Alerts
A magnitude 4.9 earthquake struck Southern California on Monday evening, centered about 12 miles north-northeast of Indio, according to the USGS.
The quake occurred just before 6 p.m. local time and was felt across parts of the Coachella Valley and surrounding areas.
The temblor was felt widely across Southern California, prompting concern among millions of residents.
As of 7 p.m. local time, four aftershocks measuring magnitude 3.0 or higher had been recorded in the Indio area, with the largest reaching a 3.5 magnitude, USGS data shows.
The USGS initially reported the earthquake as 5.1 magnitude, then revised it down to 4.6 before settling on the final measurement of 4.9.
This adjustment highlights the complexity of real-time seismic data analysis during active earthquake events.
Millions across the region received emergency alerts on their phones seconds before the earthquake struck, according to Patch.
The alerts, part of California’s early warning system, showed that the quake was 5.1 magnitude the originally assessed 5.1 the quake measured magnitude 5.1, based on the USGS’s preliminary assessment.
According to the Southern California Seismic Network, additional aftershocks are expected in the coming days, with the largest anticipated to be approximately one magnitude unit smaller than the mainshock.
However, seismologists noted a small chance—approximately 5 percent—that a larger earthquake could occur, though this likelihood decreases with time.
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