Wabash Valley Seismic Zone
Encyclopedia
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
region located in the Midwest of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, centered on the valley of the Lower Wabash River
Wabash River
The Wabash River is a river in the Midwestern United States that flows southwest from northwest Ohio near Fort Recovery across northern Indiana to southern Illinois, where it forms the Illinois-Indiana border before draining into the Ohio River, of which it is the largest northern tributary...
, along the state line between southeastern Illinois and southwestern Indiana
Southwestern Indiana
Southwestern Indiana is a 11-county region of Indiana located at the southernmost and westernmost part of the state. As of the 2000 census, the region's combined population is 465,338. Evansville, Indiana's third largest city, is the primary hub for the region as well as the primary regional hub...
.
Geology
The Wabash Valley Seismic Zone consists largely of vertically-oriented ("normal") faults deeply buried under layers of sediment. Although the tectonics of the region are still not fully understood and are the subject of ongoing research, these faults are thought by some to be associated with a branch of the New MadridNew Madrid Seismic Zone
The New Madrid Seismic Zone , sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.The New Madrid fault system was responsible for the...
aulacogen
Aulacogen
In geology, an aulacogen is a failed arm of a triple junction of a plate tectonics rift system. A triple junction beneath a continental plate initiates a three way breakup of the continental plate. As the continental break-up develops one of the three spreading ridges typically fails or stops...
, an old rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
zone where the lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
actively began to pull apart at perhaps two separate times in the distant past.Present-day GPS measurements show that the region deforms at about 1-2 mm/yr with compression along the Wabash Valley Fault Zone, and extension in SW Indiana [Hamburger et al., 2002; Galgana and Hamburger, 2010]. The crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
in the area has been weakened by the numerous faults, which remain active sites for continuing seismic activity as the motion of the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
exerts both compressional and tensional forces.
Earthquakes
This zone has been proven to have had earthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s for the last 20,000 years, with geologic evidence that they may have been as strong as 7.0-7.5 or greater on the Richter magnitude scale
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....
.
According to the United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
, lesser earthquakes occur relatively frequently, but those at a magnitude of less than 3.5 or so are usually not felt. Ones strong enough to feel usually happen once or twice a year, and those large enough to cause moderate damage have occurred every decade or so. Quakes in this region can be felt in a much wider range than those in other zones such as California
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
.
The concern of seismologists Douglas Wiens and Michael E. Wysession
Michael E. Wysession
Michael E. Wysession is currently an Associate Professor of Earth and Planetary Sciences at Washington University in St. Louis, and author of numerous science textbooks with Pearson Education and Prentice Hall. He earned his Sc.B. from Brown University in 1980 and his Ph.D...
of Washington University in St. Louis
Washington University in St. Louis
Washington University in St. Louis is a private research university located in suburban St. Louis, Missouri. Founded in 1853, and named for George Washington, the university has students and faculty from all fifty U.S. states and more than 110 nations...
, is that the New Madrid Fault may be becoming less active, while activity on the Wabash Fault could be increasing. Wiens states: "I think everyone's interested in the Wabash Valley Fault because a lot of the attention has been on the New Madrid Fault, but the Wabash Valley Fault could be the more dangerous one, at least for St. Louis and Illinois." "The strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation."
"Numerical modeling indicates that stress transfer following the 1811-1812 New Madrid earthquakes may be loading faults in the Wabash Zone."
Notable modern earthquakes in this zone include:
June 18, 2002 magnitude 4.6: The earthquake was located close to Evansville, Indiana
Evansville, Indiana
Evansville is the third-largest city in the U.S. state of Indiana and the largest city in Southern Indiana. As of the 2010 census, the city had a total population of 117,429. It is the county seat of Vanderburgh County and the regional hub for both Southwestern Indiana and the...
, with an epicenter between Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
and Cynthiana
Cynthiana, Indiana
Cynthiana is a town in Smith Township, Posey County, Indiana, United States. The population was 545 at the 2010 census. It was founded in 1817 and named for Cynthiana, Kentucky, where the first settlers had come from.-Geography:...
in Posey County. There was minor damage associated with the earthquake.
April 18, 2008 magnitude 5.4: The initial magnitude 5.4 quake was followed by a 4.6 aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
six hours later, followed by a 4.0 aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
3 days later. Its epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
was located about 41 miles (66 km) NNW of Evansville, Indiana, near the communities of West Salem
West Salem, Illinois
West Salem is a village in Edwards County, Illinois, United States. The population was 1,001 at the 2000 census.-Earthquake:West Salem is within the Wabash Valley seismic zone. On April 18, 2008 at 09:36:56 UTC a moderate earthquake of 5.2 magnitude was centered near the village...
, Mount Carmel
Mount Carmel, Illinois
Mount Carmel is a city in and the county seat of Wabash County, Illinois, United States. At the time of the 2000 census, the population was 7,982, while the next largest town in Wabash County is Allendale, population 528. Located at the confluence of the Wabash, Patoka, and White Rivers, Mount...
, and Bellmont
Bellmont, Illinois
Bellmont is a village in Wabash County, Illinois. The population was 297 at the 2000 census.-Geography:Bellmont is located at . According to the United States Census Bureau, the village has a total area of , all of it land...
. The quake was felt as far away as Kansas City
Kansas City, Missouri
Kansas City, Missouri is the largest city in the U.S. state of Missouri and is the anchor city of the Kansas City Metropolitan Area, the second largest metropolitan area in Missouri. It encompasses in parts of Jackson, Clay, Cass, and Platte counties...
, Atlanta, and Canada. Some minor damage was reported near the epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
.