Slower movements are known as creeps and in both cases, the faults can extend from just a few millimetres to thousands of miles.
Professor Farrell said on December 7: “At this point, it doesn’t look like the current swarm beneath Yellowstone Lake will approach the size of some of the larger swarms that have occurred in the past few decades, but one never knows how things are going to go, especially when it comes to earthquakes.
“We will continue to keep an eye on this swarm and see how it progresses – you can follow along by checking the seismicity map at the University of Utah Seismograph Stations website!.
“One thing is for certain, Yellowstone will continue to have earthquake swarms like this in the future.
“They are as much a part of the life of Yellowstone as the geysers and hot springs, and they are all a manifestation of the incredibly dynamic nature of the region!”