Magnitude 4.0 - ILLINOIS
2008 April 21 05:38:29 UTC
- This event has been reviewed by a seismologist.
|Depth||10 km (6.2 miles) set by location program|
|Distances||35 km (20 miles) SE of Olney, Illinois|
35 km (20 miles) SW of Vincennes, Indiana
60 km (40 miles) NNW of Evansville, Indiana
210 km (130 miles) SE of SPRINGFIELD, Illinois
|Location Uncertainty||horizontal +/- 3.9 km (2.4 miles); depth fixed by location program|
|Parameters||NST= 97, Nph= 97, Dmin=33.9 km, Rmss=1.29 sec, Gp= 25°,|
M-type=centroid moment magnitude (Mw), Version=Q
- 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.
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 11:38 PM MDT, Apr 20, 2008 (12:38 AM CDT, Apr 21, 2008 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.
Felt (IV) at Albion, Allendale, Bridgeport, Crossville, Flora, Grayville, Louisville, Mount Carmel, Olney, Sumner, Vandalia and West Salem, Illinois. Felt (V) at New Harmony; (IV) at Cynthiana, Fort Branch, Haubstadt, Owensville, Princeton, Vincennes and Wadesville, Indiana. Felt (III) in much of southern Illinois, southwestern Indiana, western Kentucky, eastern Missouri and northwestern Tennessee. Felt from Aurora, Illinois and Clinton, Iowa south to Pegram, Tennessee and from Columbia, Missouri east to Ottawa, Ohio.
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).
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.
- Preliminary Earthquake Report
- U.S. Geological Survey, National Earthquake Information Center:
World Data Center for Seismology, Denver