Chances of so many in such a short time are `` Powerball kind of odds , '' scientist says . More than two dozen since Wednesday were centered near Morrilton , Arkansas . One suspect is natural gas exploration using hydraulic fracturing , known as fracking . ( CNN ) -- The U.S. Geological Survey said the number was at least 1,500.
Chances of so many in such a short time are `` Powerball kind of odds , '' scientist says . More than two dozen since Wednesday were centered near Morrilton , Arkansas . One suspect is natural gas exploration using hydraulic fracturing , known as fracking . The U.S. Geological Survey said the number was at least 1,500.