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!
By saving cost and energy, the lighting revolution may increase light pollution
23.11.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Frictional Heat Powers Hydrothermal Activity on Enceladus
23.11.2017 | Universität Heidelberg
Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
23.11.2017 | Life Sciences
23.11.2017 | Earth Sciences
23.11.2017 | Earth Sciences