The earthquake appeared to rival the strongest recorded in the region.
The quake hit just before 4:37 a.m. and was centered six miles from West Salem, Ill., and 66 miles from Evansville, Ind. It was felt in such distant cities as Chicago, Cincinnati, Milwaukee, and Des Moines, Iowa, 450 miles northwest of the epicenter, but there were no early reports of injuries or significant damage.
Initially reported as a 5.4-magnitude earthquake, the USGS revised its estimate to 5.2. There also were several aftershocks.
The largest one so far was centered 5 miles of West Salem, according to the USGS and was a 4.5 magnitude. Two others measured 2.6 and 2.5.
``There are aftershocks going on right now,'' the agency's Gary Patterson said from Memphis. ``I can assure you, there are dozens.''
The largest historical earthquake in the region, which was also a 5.4 magnitude, damaged southern Illinois in 1968.
The National Weather Service said it has received reports from residents as far north as Lake County and the quake could be felt in the Romeoville office.
In Chicago, the city’s 911 call-center had an immediate spike in calls from people reporting tremors, Fire Media Affairs Director Larry Langford said.
The quake occurred in the Illinois basin-Ozark dome region that covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis, according to the U.S. Geological Survey.
The survey’s Web site said earthquakes occur irregularly in the area.
More than 100 calls came into the 911 call-center for the earth shaking, Office of Emergency Management and Communications spokeswoman Jennifer Martinez said.
“For the most part, people are reporting they felt movement and some items vibrated on shelves and some ceiling fixtures could be seen moving,” Langford said.
The fire department said nobody has been injured, Langford said. There have been no reports of significant structural damage to area buildings.
In Plainfield, a police dispatcher said multiple people reported their houses being shaken. She said the quake was not felt in the police station.
According to the U.S. Geological Survey the depth of the earthquake was 5.0 kilometers.
Langford said the fire department immediately contacted Chicago Police and OEMC after receiving reports of tremors.
Today, coincidentally is the anniversary of the San Francisco earthquake in 1906.
West Salem is in Edwards County in Southern Illinois, and dispatcher Lucas Griswold says the sheriff's department received several calls about the earthquake but only reports of minor damage and no injuries.
``Oh, yeah, I felt it. It was interesting,'' Griswold said. ``A lot of shaking.''
Residents in Milwaukee, Cincinnati and St. Louis also reported feeling the earth shake.
``It shook our house where it woke me up,'' said David Behm of Philo, 10 miles south of Champaign. ``Windows were rattling, and you could hear it. The house was shaking inches. For people in central Illinois, this is a big deal. It's not like California.''
Phones started ringing at the Crawford County Sheriff's Department in Robinson, about 15 miles north of the epicenter, but there were no immediate reports of damage, dispatcher Marsha Craven said.
``They didn't know if it was the refinery blowing up or an earthquake,'' she said, referring to the a local petroleum refinery.
Craven said she's lived in the area her whole life, and felt a handful of earthquakes, but couldn't recall one this big.
In Cincinnati, one woman said she felt something that lasted for up to 20 seconds.
``All of a sudden, I was awakened by this rumbling shaking,'' said Irvetta McMurtry, 43. ``My bed is an older wood frame bed, so the bed started to creak and shake, and it was almost like somebody was taking my mattress and moving it back and forth.''
WBBM Newsradio 780 has gotten dozens of calls from people in the Chicago area reporting what felt like an earthquake.
Calls were received from Dixon, Gary (Ind.), Elmhurst, Crete, Lisle, Orland Park, Chicago, St. Charles, Naperville, Elgin and Westmont.
The tremor was felt in the CBS 2 studios at 630 N. McClurg Ct., where audiovisual equipment and other items shook as the staff prepared for the news, and many of the staff reported the building shook.
Police scanner traffic also indicated that it was felt throughout the city and across the northern Illinois.
The New Madrid Fault is the largest center for seismic activity in the area. It was not immediately learned if the New Madrid Fault was origin of the earthquake.
On the Net: U.S. Geological Survey http://www.usgs.gov/
The following is a release by the United States Geological Survey, National Earthquake Information Center:
An earthquake occurred 35 km (20 miles) SW of Vincennes, Indiana and 205 km (125 miles) SW of INDIANAPOLIS, Indiana at 3:36 AM MDT, Apr 18, 2008 (4:36 AM CDT in Illinois). The magnitude and location may be revised when additional data and further analysis results are available. There have been no reports of damage.
Tectonic Summary
EARTHQUAKES IN THE ILLINOIS BASIN - OZARK DOME REGION
This large region borders the much more seismically active New Madrid seismic zone on the seismic zone's north and west. 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. The largest historical earthquake in the region (magnitude 5.4) damaged southern Illinois in 1968. Moderately damaging earthquakes strike somewhere in the region each decade or two, and smaller earthquakes are felt about once or twice a year. In addition, geologists have found evidence of eight or more prehistoric earthquakes over the last 25,000 years that were much larger than any observed historically in the region.
Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).
FAULTS
Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most bedrock in the Illinois basin – Ozark dome region was formed as several generations of mountains rose and were eroded down again over the last billion or so years.
At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Illinois basin - Ozark dome region is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean, in the Caribbean Sea, and in the Gulf of California. The region is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few earthquakes in the region can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the Illinois basin – Ozark dome region is the earthquakes themselves.
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