By Jessianne Wright EBS Contributor
BIG SKY – At approximately 12:30 a.m. July 6 a magnitude 5.8 earthquake struck western Montana, originating near Lincoln and rocking the ground in Big Sky. This earthquake comes at what appears to be the tail end of a recent earthquake swarm in Yellowstone, and experts are saying the earthquake events are unrelated and actually quite normal.
Mike Stickney, the director of the Earthquake Studies Office for the Montana Bureau of Mines and Geology attributes the Lincoln earthquake to what’s called the intermountain seismic belt within Montana, Wyoming, Idaho and Utah.
“All earthquakes develop by a slip in the fault,” Stickney said, explaining that for one reason or another, rock deep within the earth moves. The location of the movement is called a fault or fault plane, and the movement, or slip, will lead to seismic waves that generate shaking in the ground. “Small earthquakes are a daily occurrence along the intermountain seismic belt,” he said.
Small earthquakes are also normal in Yellowstone National Park, however they are caused by a different kind of seismic activity. A portion of Yellowstone National Park rests on one of the world’s largest active volcanoes, commonly known as the Yellowstone Caldera or Supervolcano. A chamber of magma is located relatively close to the surface of the earth in Yellowstone, and is responsible for the regular eruption of Old Faithful and other hydrothermal activity, as well as daily earthquakes.
Yellowstone volcanologist and geologist Jeff Hungerford recently broadcasted a statement for the park, saying, “Yellowstone National Park is a beautiful, wonderful place because it is a [seismically] active area.”
“Recognize that when you come into the park, you might feel an earthquake if you’re very lucky,” he said, explaining that most of the daily earthquakes are hardly detectable. “Occasionally we do get a big earthquake that might shake a little rock off a cliff or something like that.”
Between June 12 and July 10 Yellowstone experienced 1,141 earthquakes, and according to geologist Jacob Lowenstern of the Yellowstone Volcano Observatory, 1,000 of those were less than magnitude 2, meaning they were very small. So far this year, the park has recorded about 1,600 earthquakes, and on average, yearly totals range between 1,000 and 3,000 earthquakes.
“At this time, it looks like we’ll be within the norm,” Lowenstern said. “These swarms are pretty common. If you live in the area long enough, you’ll probably feel them.”
While an earthquake can raise alarm in a community, Lowenstern says there’s no reason to be concerned the Yellowstone Supervolcano is about to erupt. “You would have to have a lot going on before you move to an eruption and these swarms aren’t anything near what is required,” he said, adding that indications of a potential eruption include swarms of earthquakes over magnitude 5, land deformation and localized explosive eruptions.
Individuals have been experiencing and recording earthquakes in and around the Yellowstone region for hundreds of years, Lowenstern said. Mineralogist Albert Peale wrote an early account of an earthquake in Yellowstone during the Hayden Geological Survey of 1871.
“This morning about 1 o’clock we had quite an earthquake,” Peale wrote in his journal on Aug. 20, 1871. “The first schock [sic] lasted about 20 seconds and was followed by five or six shorter ones. Duncan, who was on guard, says that the trees were shaken and that the horses that were lying down sprang to their feet. Some birds in the tree near which I had my bed were wakened and flew out of its branches. Some of the men were not wakened at all. We had three shocks during the morning.”
Earthquakes in western Montana and Yellowstone have been studied and recorded for several decades now, Lowenstern said. Yellowstone National Park has approximately 35 and according to Stickney, MBMG monitors data from about 85 stations throughout Montana, Wyoming, Idaho, Washington and Canada. These instruments monitor ground vibrations and shakes, which can be recorded and used to give a magnitude as well as locate the epicenter, depth and time.
The magnitude of an earthquake indicates how much energy was released based on the motion of the ground. “Each time you go up one number on the scale, the amount of ground-shaking goes up by ten,” Stickney said. Earthquakes of magnitude 2.5 and smaller are barely detectable, while those of magnitude 5 and greater have potential to cause damage.
The recent earthquake swarms in Yellowstone have not caused any damage, Lowenstern said. Over the past year the caldera has slowly been moving down while the Norris area is slowly moving up, but the recent swarms have not caused any changes to these trends in ground deformation, he added. The magnitude 5.8 earthquake in Lincoln caused some structural damage to area buildings, reportedly knocking food off grocery store shelves and sloshing grease out of a fryer at Lincoln’s Wheel Inn Tavern.
“The recent activity is a reminder that we live in earthquake country and that a big one could always come along,” Stickney said. “But the recent seismic activity appears to be a part of normal operations for the area that we live in.”