In the year 1556, in north-central China, the largest earthquake ever recorded shook a several-hundred-mile area. Contemporary accounts describe buildings crumbling, the earth liquefying and an estimated 830,000 dead beneath the rubble.
Just more than 250 years later, a slightly less powerful quake and aftershocks shook Missouri and the Mississippi Valley in 1811-12. At the time, the mighty river was reported to have run backward, church bells rang as far away as Boston, and thousands died.
These two earthquakes have something in common that has stumped scientists ever since: Both occurred in the middle of a tectonic plate in the Earth’s crust, instead of at its edges. Called “intraplate” events, these earthquakes happen at large intervals often more than 500 years and are some of the Earth’s most catastrophic. But scientists today are still largely in the dark about their cause.
“We still don’t understand why we have earthquakes in Missouri. We are in the middle of this stable North American plate. We are not in the boundary. We are not bumping into another plate. But nonetheless we have big earthquakes here,” said Mian Liu, a geologist at University of Missouri-Columbia.
Liu and other University of Missouri researchers from the department of geological sciences plan to bring together students from the Chinese and American quake zones to do important research they hope will shed new light on intraplate earthquakes. Liu and his colleagues recently announced they received a $2.16 million grant, the largest of its kind in the department’s history, from the National Science Foundation.
The researchers, along with 35 University of Missouri graduate and undergraduate students, will travel to northern China over the next five years to work with students from two top Chinese universities. The Missouri grant application was one of 12 selected out of a pool of more than 500 to be part of the federal program called Partnerships for International Research and Education.
“This is such a big deal, not just for geophysics but for MU in general,” said Kevin Shelton, chairman of geological sciences at the university. “We’re a relatively small department at a relatively modest university, but on some levels this shows we can compete with the big boys.”
Students will attack the problem using three different cutting-edge techniques. With X-ray-like equipment they will take images as far as several hundred kilometers into the Earth’s interior. Liu said it’s the best way to diagnose what’s going on.
“If you have a headache, and no one can see why you have a headache, maybe a doctor uses a CAT scan to see if you have a tumor there. So when we have earthquakes, we want to have this kind of image. If there is a fault, or maybe it’s mechanically weak,” he said.
Students will also use GPS and space-based surveying techniques capable of measuring motion as small as a millimeter per year to determine how fast the faults are moving. Intraplate faults are mysterious because their motion is often too small to be detected.
“An earthquake basically releases the stored energy in the crust, but if it’s not moving you have a harder time to explain this energy that’s accumulating there,” Liu said. “We just don’t have a very good understanding of the basic physics.”
Finally, students will integrate the data to reconstruct and simulate historical earthquakes on computers.
The undertaking will be massive, but it represents more of a true partnership with China than has ever existed before in geology. China will be providing most of the equipment and has spent $20 million in its northern region to study the earth structure. In fact, China is now installing 800 seismometers, or tremor measuring devices, across the region. The United States in a similar project is installing 400 of the costly instruments across the country.
China has experienced 50 major intraplate quakes in the past 700 years, and its earthquake-prone northern region is the country’s most highly developed. China is definitely taking earthquakes seriously.
“It’s a good opportunity for us to jump onto this bandwagon,” said Liu. “Projects of the NSF and the U.S. Geological survey are increasingly international collaborations, and that’s why NSF wants the next generation of scientists and engineers to be globally engaged, have a global perspective and also global connections.”
Information from: Columbia Daily Tribune, http://www.columbiatribune.com
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