Chart shows average daily earthquakes in Oklahoma by month in 2016; 2c x 3 inches; 96.3 mm x 76 mm;
Chart shows average daily earthquakes in Oklahoma by month in 2016; 2c x 3 inches; 96.3 mm x 76 mm; Credit: k.vineys

Washington — The rate of earthquakes in Oklahoma has dropped dramatically since late May, when the state limited wastewater injections from hydraulic fracturing, or fracking, into energy wells, an Associated Press statistical analysis shows. And a new scientific study says the state is on its way back to calmer times that prevailed before a huge jump in man-made quakes.

For quake-prone parts of Oklahoma, the state ordered what is essentially a 40 percent reduction in injection of the saltwater that scientists generally blame for the massive increase in earthquakes. This year, before the new rules went into effect on May 28, Oklahoma averaged 2.3 quakes a day.

Since then the average dropped to 1.3 a day, based on AP’s analysis of U.S. Geological Survey data of earthquakes of magnitude 3.0 or larger. But some of those fewer post-regulatory quakes have been large and damaging.