A new United States Geological Survey study has found that middle America between Alabama and Montana is experiencing an "unprecedented" and "almost certainly manmade" increase in earthquakes of 3.0 magnitude or greater. In 2011, there were 134 events of that size. That's six times more than were normally seen during the 20th century.
While the changes in the area's seismicity began in 2001, the trend has really accelerated since 2009, the geologists note. That happens to coincide with increased oil and gas production using new extraction techniques in some parts of the area.The new work is being presented at the Seismology Society of America's conference later this month. An abstract for the presentationis available online.
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