EDMOND, Oklahoma - It's the question being asked across the state. Why are so many earthquakes rocking Oklahoma? Four hit Edmond Monday.

The answer may come from California.

A group of geophysicists are studying what they're calling "induced earthquakes," or quakes caused by human activity. The number of earthquakes to hit parts of Oklahoma have skyrocketed since 2009.

"It was a little unnerving," said North Edmond resident, Ken Janz.

The number of earthquakes felt over the last few years in Oklahoma have without a doubt been unusual. But, for Edmond resident Ken Janz and his family, it's almost becoming the norm.

The latest earthquake was a 3.3 magnitude around 3:15 Monday afternoon outside Edmond.

"It didn't sound like the last earthquake I was in, it was more just a loud boom, house shook momentarily," said Janz. "I thought maybe a tree or something had fallen over and hit the house."

"We've been aware of earthquakes caused by human activity for many, many, years," said California Research Geophysicist, Justin Rubinstein.

Rubinstein is part of group out of California trying to understand and characterize earthquakes that are caused by human activity.

"Examining earthquakes that are ongoing and trying to understand whether or not they are related to industrial activities or not, or if they're just naturally occurring," Rubinstein said.

Since 2009, the group has come across some very interesting discoveries.

"From the Rocky Mountains eastward, we've seen a large increase in earthquake rate of magnitude 3 and larger earthquakes," Rubinstein said.

From 2009 and forward, that increase is even larger. According to Rubinstein, a significant percentage of those earthquakes are coming from Oklahoma.

"That's a pretty remarkable finding," Rubinstein said.

"It's a concern," Janz said.

In the past seven days, the Oklahoma Geological survey has recorded just over 100 earthquakes, including the largest one in the past week, a 3.8 in Choctaw.