A total of 130 earthquakes shook Yellowstone National Park between Sept. 10 and Sept. 15, according to a University of Utah press release, though most were too small for a person to feel.

Bob Smith is a geophysicist who has spent the last 53 years monitoring seismic activity in and around the Yellowstone Caldera. During this time, he told The Associated Press, he only recently witnessed two simultaneous earthquake swarms, or groupings. Then, last week, he detected three.

"It's very remarkable," Smith said. "How does one swarm relate to another? Can one swarm trigger another and vice versa?"

The answers aren't clear, though Smith said he "wouldn't doubt" if at least two of the swarms were related.

According to the University of Utah Seismograph Stations, the sequence of swarms began on Sept. 10 and have concentrated around Lewis Lake, the Lower Geyser Basin and northwest of Norris Geyser Basin.

"Notably much of the seismicity in Yellowstone occurs as swarms," the press statement notes.

"This is pretty unusual, to be honest," Smith said, explaining that an earthquake generally isn't felt until it reaches a magnitude of 3.0 on the Richter scale. The range for the latest swarms have fallen between 0.6 and 3.6.

"We know that a significant enough earthquake in the region has potential to alter geyser activity," park spokesman Al Nash told the Jackson Hole News & Guide. "A strong enough earthquake, like the one that occurred out at Hebgen Lake in 1959, did change the interval of Old Faithful eruptions."

The 1959 earthquake registered a 7.3 to 7.5, causing nearly 300 locations within Yellowstone to erupt. According to the AP, Smith traced all three recent swarms back to the Hebgen Lake quake.

"We think that much of the seismicity is still aftershocks from that event in 1959," he said. "It can go on for hundreds of years."

According to the University of Utah press release, the school's seismograph stations will continue "to monitor Yellowstone earthquakes and will provide additional information if the earthquake swarm activity increases."