reply to post by TheRedneck
Could liquefaction over eons cause a fault to heal itself, sort of like welding the plates back together? And could the Midwest be sitting atop such a
healed area in a much larger New Madrid Fault Zone than was originally thought? And could that mean that there is an inherent weakness in this area
that is just now reforming into an active fault zone, accelerated by the release of restraining pressure from the BP oil well disaster?
Those are great questions.
Let me start by explaining some of the factors in that area. As I believe someone mentioned, there is another fault zone near the NMFZ, called Wabash
Valley Seismic Zone. In fact, that zone is believed by geologists, to be the one of the oldest fault zone on earth, dating back to the PreCambrian
The Wabash Valley Seismic Zone has produced earthquakes for the past 20,000 years, with some registering 7.5 on the Richter magnitude scale.
Seismologists believe that the Wabash Valley fault dates from Precambrian times, the oldest era of the Earth's history, and that the fault has been
reactivated. Read more: The History of Wabash Valley Seismic Zone | eHow.com
Here is a link to a map of the two zones:
Many geologists believe the 2 zones connect:
Centered in the Wabash River Valley, the Wabash Valley Seismic Zone straddles the state line between southeastern Illinois and southwestern Indiana
and spreads into part of western Kentucky. Scientists believe that it is a branch of the New Madrid system, which extends south from Cairo, Illinois,
through Missouri, Arkansas, Mississippi and parts of western Tennessee, according to the Arkansas Center for Earthquake Education and Technology
Now enter a third fault, recently discovered:
The 1968 Illinois earthquake or New Madrid event, hit Illinois on November 9, 1968, and measured 5.4 on the Richter scale. It affected 23 states over
an area of 580,000 square miles, causing much structural damage to buildings but no fatalities. In researching its cause, scientists discovered the
Cottage Grove Fault in the Southern Illinois Basin, which is a small tear in the Earth's rock running west to east under Saline County, near
Harrisburg, Illinois. It connects to the north-south running Wabash Valley Fault System at its eastern end.
Dr. Won-Young Kim, a seismologist at the Lamont-Doherty Earth Observatory at Columbia University, investigated the probabilities of future
earthquakes in the Wabash Valley Seismic Zone.
He discovered that an ancient fault line from the Precambrian era--4.6 billion to 570 million years ago--has reactivated and probably caused the 2002
earthquake. According to Dr. Won-Young Kim, "This area was once as seismically active as the Gulf of California is today. The reactivation of this
fault may be due to the forces that are moving the North American Plate over the Earth's mantle. The depth of this earthquake suggests that these
forces are quite large, even though they are far away from present plate boundaries."
On April 18, 2008, the 102nd anniversary of the 1906 San Francisco earthquake, a magnitude 5.2 earthquake struck near the community of West Salem,
Illinois. It jolted communities across southern Illinois, southern Indiana, western and central Kentucky and eastern Missouri. People in Chicago and
St. Louis, 123 miles away, felt its vibrations.
Seismologists and geologists at St. Louis University predict that a future earthquake in the region is likely, forecasting a 90 percent chance of a
6.0 magnitude earthquake, or greater, before 2040. They say it will very likely originate in the Wabash Valley Seismic Zone or in the New Madrid Fault
For those interested in the technical details of seismic activity in the above areas, I recommend:
Munson, P. J., S. F. Obermeier, C. A. Munson, and Hajic, E. R., 1997, Liquefaction evidence for Holocene and latest Pleistocene seismicity in the
southern halves of Indiana and Illinois: A preliminary overview. Seismological Research Letters, v. 68, p. 521-536.
Here is a brief synopsis of the paper:
Clastic dikes filled with sand and gravel, interpreted to be the result of earthquake-induced liquefaction, occur throughout much of southern
Indiana and adjacent parts of Illinois. At least seven and probably eight prehistoric earthquakes have been documented during the Holocene, as well
as, at least one during the latest Pleistocene. Nearly all of these liquefaction features originated from earthquakes centered in southern Indiana and
Illinois, and not further south in the nearby source region of the great 1811-1812 New Madrid earthquakes. The recognition of different earthquakes is
based mainly on defining limits on the timing of liquefaction features in combination with the regional pattern of liquefaction effects, but some
earthquakes have been recognized only by geotechnical testing at sites of liquefaction. Prehistoric magnitudes were probably on the order of moment
magnitude M 7.5, which greatly exceeds the largest historical earthquakes of M 5.5 in the region. The strongest prehistoric earthquakes had epicenters
in the vicinity of the lower Wabash Valley, where the valley borders both Indiana and Illinois. The evidence of Quaternary faulting in the Wabash
Valley area is based on the presence of liquefaction features. Liquefaction features are evidence of strong shaking, but they do not identify the
specific fault that caused an earthquake. Because individual Quaternary faults remain unidentified, it is not possible to define and measure specific
attributes (azimuth, length, dip, etc.) for the Wabash Valley liquefaction features.
As this paper describes, liquefaction was certainly a major factor in this area;however, the SPECIFIC fault that caused each earthquake has NOT been
For those that want a brief explanation of Quaternary faults, I suggest this link:
Thus, my good friend, your theory certainly is along the right line of thinking, and if you can prove your hypothesis, you would certainly have your
name in lights with the Geological Society. I applaud your insight.
By the way, Happy New Year.