(Bloomberg) -- After six earthquakes rattled the Permian Basin over the past 19 months, the Texas oil regulator is asking drillers to cut back on the amount of dirty water they’re pumping underground.

Oil producers’ disposal of wastewater from fracking is probably contributing to seismic activity in an area of the Permian’s Midland Basin, the Texas Railroad Commission said Friday in a notice. The restrictions on water disposal are expected to be in place for at least a year, the commission said. It’s a fairly unusual move by the regulator, which hasn’t been as active as its counterpart in Oklahoma in trying to prevent earthquakes linked to fracking. 

Shale drillers’ disposal of the massive amounts of water they use to break apart rock layers, along with the water naturally produced over the life of the well, has long been linked to earthquakes. The tremors are getting more frequent. Earthquakes registering at least a 2 on the Richter scale quadrupled from 2017 levels to a record 938 last year and are on pace to top that this year, according to a Rystad Energy analysis of data in Oklahoma, Texas, Louisiana and New Mexico released in June.

The increased tremors and huge volumes of wastewater have added to environmental concerns surrounding oil and gas production from shale fields. Drillers have come under intensifying scrutiny in recent years, with companies under pressure from investors to disclose climate risks and reduce greenhouse gas emissions.

Texas regulators said in the notice Friday that the six earthquakes in the Midland and Odessa area since February 2020 registered at least a 3.5 magnitude. The commission identified 76 saltwater disposal wells in the area affected by the seismic activity.

©2021 Bloomberg L.P.