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‘These are different:’ Earthquake sequence in Southern Utah

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Courtesy: UUSS

MILFORD, Utah (ABC4) – According to the University of Utah Seismograph Stations, UUSS, there is currently an energetic earthquake swarm occurring south of Milford, Utah.

UUSS officials took to Twitter, saying an earthquake swarm is an earthquake sequence with no clear mainshock. Earthquake swarms are often associated with fluids or in areas of weak crust.

The earthquake swarm south of Milford is unlike Magna’s March 2020 sequence where the largest earthquake occurred first followed by aftershocks with magnitudes distinctly smaller than the mainshock.

In a swarm, the larger events often occur later by hours to days in the sequence and there can be multiple larger earthquakes with similar magnitudes, like March 28-29.

Below are some of March’s earthquakes:

Dr. Kristine Pankow, Associate Director for the University of Utah Seismograph Stations and a research professor in the department of geology and geophysics, tells ABC4 the Milford sequence has been going on since at least March 20, with the largest earthquake being 3.2 magnitude.

Dr. Pankow says an earthquake sequence is any collection of earthquake events and is classified in three ways. A mainshock, aftershock sequence, like Magna. The largest event of the sequence being the first, then followed by possibly thousands of aftershocks.

In most cases, the aftershocks are smaller in magnitude. “Clear separation that the mainshock is larger than the aftershocks,” Dr. Pankow adds. “Aftershocks are kinda the chatter, catching up with how it moved.”

The second type of sequence is a foreshock, mainshock, aftershock, Dr. Pankow explains. “This is a lot like Magna, except the sequence starts with a smaller event or a handful of smaller events.”

Utah’s Magna earthquake did not have a foreshock.

Third, swarms. Like what is currently happening in Milford. “These are different,” Dr. Pankow shares.

In the swarm, there is still a mainshock, but it is not typically that much larger.

“Big events don’t have to happen at the beginning of the sequence. You don’t have to have one big event and a bunch of smaller events,” Dr. Pankow shares. “We get other swarms in Utah, it is not all that unusual to have swarm earthquakes in Utah.”

Dr. Pankow says swarm earthquake sequences don’t always garner a lot of attention because they typically don’t have large magnitudes. Magnitudes are typically smaller than people would be concerned over, Dr. Pankow adds.

The earthquakes in Milford are a little larger, causing more people to notice them despite not being damaging, but “definitely have the characteristic of a swarm.”

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