Yellowstone earthquake swarm
© USGS
Almost 770 earthquakes have been recorded in Yellowstone Park over the past two weeks — more than normal but not a sign of volcanic activity, scientists say.

As of 11:30 Friday morning, 769 quakes had been recorded in the current swarm, said Jamie Farrell, a research professor of seismology at the University of Utah.

The swarm, which began June 12, is ongoing, he added, though the frequency of earthquakes has slowed down a bit. Typical swarms comprise 10 to 50 quakes, Farrell said.

"As of now, everything that we can see looks like these are tectonic in origin," he said. "There's no volcanic signature to any of these events that we've found."

The university's seismograph stations have tracked a single quake in the magnitude 4 range, a temblor near West Yellowstone on June 15 that has been the largest of the swarm to date.

So far, five quakes have measured in the magnitude 3 range and 64 in the magnitude 2 range. The other 699 have been measured at magnitude 1 or less, Farrell said.

According to the U.S. Geological Service, earthquakes in the magnitude 1-3 range might not be felt at all, except under a few especially favorable conditions.

Quake swarms are common in Yellowstone and other volcanically active areas, Farrell said.

Yellowstone is one of the most seismically active areas in the U.S., experiencing 1,000 to 3,000 earthquakes a year — with 40 to 50 percent of them happening in swarms. The quake activity is caused by the large number of faults in the park associated with the volcano that underlies Yellowstone.

According to the National Park Service, the largest swarm happened in 1985, when more than 3,000 quakes were recorded in a three-month period in the northwestern portion of the park.