2016-09-06. Scientists may have solved mystery of giant Midwest earthquakes.

posted Sep 11, 2016, 7:28 AM by Alan Gould   [ updated Sep 11, 2016, 7:31 AM ]
By Elizabeth Deatrick, Science. For GSS Energy Flow chapter 3. Excerpt: Two centuries ago, a series of giant earthquakes rocked the tiny town of New Madrid, Missouri, collapsing chimneys and shaking houses more than 1000 kilometers away. It was even said that parts of the Mississippi River momentarily flowed backward as the riverbed heaved upward. ...Even today, the New Madrid Seismic Zone (NMSZ) generates more than 200 small tremors each year—and now a team of geophysicists thinks it knows what causes all the shaking. ...In a new study, they use tomographic information about Earth’s interior to show how blobs of dense rock from the lower crust rise up underneath the region. This dense rock gravitationally tugs on everything else around it, changing regional stresses in a way that makes some NMSZ faults more likely to slip. ...“We’re interested in creating an honest-to-goodness map of where we think earthquakes will occur in the future,” says lead author Will Levandowski, a geophysicist with the United States Geological Survey (USGS) in Golden, Colorado. ...Experts say the work could be used to explain why some areas are more prone to human-induced earthquakes, such as Oklahoma, which now sees more earthquakes than California. Fracking-related activities might be more likely to trigger an earthquake in an area that was already under stress, according to Roland Bürgmann, a geophysicist at the University of California, Berkeley....  http://www.sciencemag.org/news/2016/09/scientists-may-have-solved-mystery-giant-midwest-earthquakes