Scientists from Northwestern University, the U.S. Army Engineer Research and Development Center and the University of Illinois at Chicago have found that New Madrid appears to be cold and dying. They will present their findings Dec. 13 at the annual meeting of the American Geophysical Union (AGU) in San Francisco.
"Hot rocks are weak," says Seth A. Stein, William Deering Professor of Geological Sciences in the Weinberg College of Arts and Sciences at Northwestern and a coauthor of the study. "So people suggested that the reason large earthquakes occur in the New Madrid area rather than in the many similar geologic settings in other parts of the eastern United States is that the New Madrid rocks are hotter."
But the researchers discovered this is not the case. They looked at data used in the new edition of the Geothermal Map of North America (American Association of Petroleum Geologists, 2004), which shows all the measurements of the heat coming to the Earth's surface (heat flow) taken from boreholes. They found that thermally New Madrid is surprisingly similar to other areas of the eastern United States.
"The New Madrid data are essentially no different from other sites in the eastern United States," explains coauthor Jason R. McKenna from the U.S. Army Engineer Research and Development Center. "Although we'd like to have more measurements to be sure, at this point, there's no reason to believe New Madrid rocks are hotter and therefore weaker than rock in other parts of the eastern United States."
One of the most difficult aspects of assessing the earthquake hazard is deciding whether New Madrid is a special place or simply where central U.S. earthquakes have occurred in the past few thousand years. "When we look at things like geology, gravity or the magnetic field, there's no obvious difference between New Madrid and similar places in the eastern United States that haven't had large earthquakes recently," McKenna notes. "Now we see the same for heat flow."
The new heat flow results fit into a growing idea that earthquakes can migrate among similar faults, some of which -- such as the Meers fault in Oklahoma -- appear to have been active about 10,000 years ago but show no activity today. Geological studies find that New Madrid earthquakes comparable to those of 1811-1812 occurred about 1450 and 900 AD. However, because this fault system has not generated significant topography, it is likely to have "turned on" relatively recently, perhaps within the past few thousand years.
With this view, say the researchers, prior earthquakes were concentrated on other faults, and future earthquakes will occur somewhere else when the New Madrid system "shuts down." Once this happens, it may be a very long time -- thousands of years or longer -- before New Madrid becomes active again.
"Although we don't know when the New Madrid fault system will shut down, it may be dying today," says Stein. "The recent cluster of earthquakes may be coming to an end."
Migrating earthquakes also occur in the interior of other continents, such as Australia. This is very different from the way earthquakes occur on boundaries between plates, like the San Andreas fault along the boundary between the Pacific and North American plates. Because the plates keep moving, earthquakes continue to occur on the boundaries in the same places.
Precise measurements taken by Stein, coworkers and other investigators using the Global Positioning System (GPS) show that motion across the New Madrid Seismic Zone currently is either very slow or at zero. Because this motion has to accumulate for many years to cause a large earthquake, it will be at least hundreds of years, and perhaps much longer, before another large earthquake happens.
"Until recently about all we could say was that future earthquakes might occur in places where past ones had," says Stein. "Now we can actually test that idea by looking at the motion accumulating for possible future earthquakes. Although we can't be sure yet, the longer the GPS data continue to show essentially no motion, the more likely it seems that the fault is shutting down and won't cause large earthquakes for a very long time. It's time to start thinking about this possibility and to use what we're learning to improve estimates of the hazard from future earthquakes."
The possibility of the fault shutting down is important for assessing the earthquake hazard in the central United States. Large earthquakes (magnitude 7) occurred in 1811 and 1812, causing shaking across much of the area. Houses collapsed in the tiny Mississippi river town of New Madrid, Mo., and minor damage occurred in St. Louis, Louisville and Nashville. The smaller earthquakes that continue in the area today are typically more of a nuisance than a catastrophe, say the researchers. The largest in the past century, the 1968 southern Illinois earthquake (magnitude 5.5), was widely felt and caused some damage but no fatalities. However, if large earthquakes like those of 1811-12 occurred again, they would be very destructive.
Megan Fellman | EurekAlert!
NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center
Steep rise of the Bernese Alps
24.03.2017 | Universität Bern
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy