OKLAHOMA CITY -- After restricting frac water injection in certain hot spots, Oklahoma is feeling an average of about two earthquakes a day, down from about six last summer, and Kansas is feeling about a quarter of the tremors it once did, according to an article in the Washington Post.

Oil and gas operators inject the wastewater into disposal wells that are thousands of feet underground, which can increase fluid pressures and sometimes cause faults to move.

Since March 2015, Kansas and Oklahoma have placed new restrictions on how much wastewater each operator in certain areas can dispose at a given time.

From 1973 to 2008, according to USGS, the Midwest region had, on average, 24 earthquakes of magnitude 3 or larger each year. The USGS tallied 1,010 earthquakes in the region last year, a number that had increased steadily from 318 in 2009. Parts of this region, including northern Oklahoma and southern Kansas, are now as seismically active as California.

In March 2015, the Kansas Corporation Commission began limiting wastewater disposal in five zones and two counties. Since then, the state has felt fewer tremors. In the last six months of 2015, there were 39 quakes of magnitude 2.8 or larger, compared with 48 quakes during the last six months of 2014. In the first six months of 2016, only 11 were recorded by USGS.

In March, the Oklahoma Corporation Commission began restricting how much wastewater operators dispose of in about 600 of its 3,800 disposal wells, in certain hot spots. Oklahoma felt 619 earthquakes of magnitude of 2.8 or greater from January through June, compared with 701 during the same time last year, according to USGS data.

Another contributing factor to reduction in earthquakes is a significant reduction in oil and gas drilling and production activities due to low commodity prices.

Regulations restricting frac water injection reducing earthquakes in Oklahoma, Kansas