BATON ROUGE - A series of rare earthquakes that shook north Louisiana this month is raising questions about what may have caused them.

According to the United States Geological Survey, a magnitude 4.9 earthquake struck near Edgefield this month. The tremor was felt across parts of Louisiana and East Texas.

In the days that followed, several aftershocks were also detected, including a magnitude 4.0 quake near Coushatta.

While researchers are still working to determine the exact cause, some advocates believe human activity could be playing a role.

Anne Rolfes, director of the Louisiana Bucket Brigade, said Monday that some seismologists have linked similar earthquakes to fracking-related activity.

“Every seismologist that I've heard speak on it says that it is connected to fracking,” Rolfes said.

Louisiana sits in the middle of the North American tectonic plate, meaning it is not typically an area with active plate movement. However, scientists say there is an ancient fault system beneath the state that could have been disturbed.

Rolfes said injecting wastewater deep underground, a practice associated with oil and gas production, could potentially make those underground structures less stable.

“They're injecting wastewater into the tectonic plates, and that is making us less stable,” she said.

Scientists have previously linked injection wells to similar earthquake activity in states like Kansas and Oklahoma about a decade ago.

Rolfes said the recent earthquakes are also raising concerns about other underground injection projects being considered in Louisiana, including proposed carbon capture storage.

“Don't we have enough with floods and hurricanes? Do we really need to create earthquakes?” she said. “Now the state is proposing to inject carbon, if you can imagine, in those same plates, and that's dangerous.”

State officials say they are working with federal scientists and researchers to determine what caused the earthquakes, but so far there is no clear link to any specific activity.

While the shaking surprised many residents, officials say there have been no reports of damage or injuries related to the earthquakes.