TULSA, Okla. (AP) — Recent earthquakes west of Perry, Oklahoma, have state regulators and scientists investigating whether regulatory action is needed in the area.

According to U.S. Geological Survey data, the five earthquakes were at depths of about 2 to 3.5 miles underground.

Oklahoma's state seismologist Jake Walter told the Tulsa World (http://bit.ly/2ss091Q ) that the "rash of activity" is "nothing that's out of the ordinary." He said Oklahoma tends to have earthquakes that "cluster like this."

Oklahoma Geological Survey director Jeremy Boak said the frequency of the earthquakes declined throughout 2016, but the frequency has flattened out or slightly increased since February.

Boak said the moving average of earthquakes of a magnitude of 2.5 or greater is about three per day, down from a peak of 10.7 per day during the height of Oklahoma's rattling.

"I'm not sure what's going on," Boak said. "The (saltwater) injection seems to be continuing downward, but slower now. So it's a little bit hard to figure out what the trend is going to be."

Oklahoma Corporation Commission spokesman Matt Skinner said regulators will be looking into saltwater disposal data of about 20 formation wells in Garfield, Logan and Noble counties related to the earthquakes near Perry.

"We've been looking at it, but it started in earnest (Wednesday) because of the grouping of the quakes," Skinner said.

He said it's too soon to tell if regulatory action is warranted.

"We're still in the investigative phase," Skinner said.