If I understand the physics correctly, earthquakes can only occur when there is significant pressure in the underground rock layers for sections of the rock layers to want to move in different directions.

This largely happens around already existing fault zones. But it can reportedly occur elsewhere such as in locations where significant amounts of oil or water are being pumped out of the ground. The ground eventually sinks and earthquakes occur as it settles into place.

Earthquakes can also reportedly occur when massive amounts of weight or mass are added to some area above the ground. This can happen when a dam is built on a river. The new reservoir of water behind the dam contains so much weight and mass that it can put a tremendous amount of pressure on nearby rock layers. And it can affect the balance of forces exerted on the Earth’s crust due to the spinning of the Earth on its axis and the gravitational pulls of the sun and the moon on the Earth.

What on Earth is going on in Arkansas?

Are there some fault zones in that area? If not, then what else would cause the rock layers to want to move in different directions?

If there are no fault zones in that area, then unless there is something else going on down there that no one knows about, those existing injection wells could look like strong suspects for the cause of that earthquake activity.