Our Morning Earth Quake Report

Those unfamiliar may say, from looking at the maps below, that Springfield, Illinois appears very far from the epicenter. And that is true in a California sense, but because of the nature of the bedrock (very solid), and the type of fault (very deep), the energy from this fault travels almost completely undisturbed right from the Wabash fault to our location here in Springfield, Illinois. So it was quite a ride this morning.


Friday, April 18, 2008 at 09:36:56 UTC

Earthquake Location

Major Tectonic Boundaries: Subduction Zones -purple, Ridges -red and Transform Faults -green

Major Tectonic Boundaries: Subduction Zones -purple, Ridges -red and Transform Faults -green

USGS Topographic Map, Resolution: 16.0 meters/pixel

1 km

USGS Aerial Photo, Resolution: 16.0 meters/pixel

1 km

Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver

Magnitude 5.4 - ILLINOIS

2008 April 18 09:36:56 UTC

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Earthquake Details

Magnitude	5.4
Date-Time	Friday, April 18, 2008 at 09:36:56 UTC Friday, April 18, 2008 at 04:36:56 AM at epicenter Time of Earthquake in other Time Zones
Location	38.520°N, 87.873°W
Depth	5 km (3.1 miles) set by location program
Region	ILLINOIS
Distances	12 km (7 miles) E (90°) from West Salem, IL 13 km (8 miles) NE (53°) from Bone Gap, IL 14 km (9 miles) W (266°) from Allendale, IL 36 km (22 miles) WSW (241°) from Vincennes, IN 67 km (41 miles) NNW (335°) from Evansville, IN 206 km (128 miles) E (93°) from St. Louis, MO
Location Uncertainty	horizontal +/- 4.1 km (2.5 miles); depth fixed by location program
Parameters	NST=135, Nph=135, Dmin=31 km, Rmss=1.61 sec, Gp= 32°, M-type=moment magnitude (Mw), Version=8
Source	USGS NEIC (WDCS-D)
Event ID	us2008qza6

• This event has been reviewed by a seismologist.
• Did you feel it? Report shaking and damage at your location. You can also view a map displaying accumulated data from your report and others.

Earthquake Summary

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.

Earthquake Information for Illinois

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Scientific & Technical Information

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• Preliminary Earthquake Report
• U.S. Geological Survey, National Earthquake Information Center:
  World Data Center for Seismology, Denver
• 
  

Here's what the local newspaper SJ-R has to say:

Updated: 5.4 earthquake rocks Illinois; also felt in Ohio and Indiana

Last Updated 4/18/2008 5:35:40 AM

By JAYETTE BOLINSKI
STAFF WRITER

Hundreds of Springfield-area residents were shaken awake this morning when they felt the rumblings of a 5.4-magnitude earthquake centered near West Salem.

No damage and no injuries have been reported here. The trembling, just before 4:37 a.m., lasted about 15 seconds.

Dispatchers at Sangamon County 911 and local police departments received numerous phone calls from residents wondering what was going on or reporting someone was in their home.

911's phone lines temporarily went down after the earthquake, but it was not immediately known if that was a result of the trembling.

The quake was centered 6 miles from West Salem, Ill., and 66 miles from Evansville, Ind.

The quake shook tall buildings in Chicago's Loop, 240 miles north of the epicenter, and in downtown Indianapolis, about 160 miles northeast of the epicenter.

Residents in 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."

The Associated Press contributed to this report.