Oklahoma regulators, working in coordination with federal authorities, closed down more wells in the state in response to an early September earthquake.

The U.S. Geological Survey recorded six seismic events in Oklahoma over the last 24 hours, the largest of which was a magnitude-3.6 tremor in Major County in the west-central part of the state.

One of the U.S. states with a significant amount of shale oil and natural gas, a study from the USGS found the disposal of oil and gas-related wastewater is the "primary reason" for an increase in seismic activity in central states like Oklahoma.

Seismic events over the last 24 hours follow a magnitude-5.3 earthquake recorded in Oklahoma on Sept. 3. Oklahoma Gov. Mary Fallin responded with a declaration of a state of emergency for the county impacted by the quake and the Oklahoma Corporation Commission's Oil and Gas Division said it was now enacting further restrictions on shale activity.

In response to the Sept. 3 quake, the state agency said it was nearly doubling the size of a so-called area of concern. Combined with areas under the authority of the federal Environmental Protection Agency, the state government said it also ordered the closure of 32 wells.

The order translates to a volume reduction of wastewater injections for wells under state jurisdiction of 40,000 barrels per day. The order, the state agency said, is mandatory and relates in large part to new fault data coming out of the Oklahoma Geological Survey and the USGS in the county impacted by the early September quake.

Wastewater injection, not hydraulic fracturing itself, is the greatest risk factor for seismic events in Oklahoma. Fielding questions about the Sept. 3 quake, White House spokesman Josh Earnest said the federal government was not changing policy related to hydraulic fracturing.