Earthquake Swarms

Kristine Pankow, U professor of geology Credit: University of Utah

Most of the earthquakes rumbling under the West’s Great Basin come in surges, clustered together in time and place. Scientists call these seismic groups “swarms,” which are a distinct category from the numerous aftershocks following a big shake, such as the 5.7 magnitude Magna quake of 2020 on the Wasatch Fault.

Rather than getting spread out evenly over time, many of these small, often imperceptible quakes strike a region in a short period of time, say a few days or weeks.

Central Utah has been the stage for dozens of earthquake swarms that have been recorded over the past 40 years by an ever-expanding network of seismic arrays managed by the University of Utah.

Now U seismologists are analyzing decades of seismic data in the hope of discerning the significance of these swarms in a geologically complex region known as a geothermal hotspot and for recent—geologically speaking—volcanism.

“In central Utah, seismic swarms are much more common than any other type of sequence. We looked into all types of sequences, but 80% of the sequences are swarms. That’s remarkable,” said Gesa Petersen, a post-doctoral research fellow. “We also saw that these are very heterogeneous. So one location in central Utah can have a very, very different behavior than other locations just 30, 40, 50 kilometers away.”

With U geology professor Kristine Pankow, Petersen published the latest findings July 13 in the journal Geochemistry, Geophysics, Geosystems. Funding came from the state of Utah and the $220 million Department of Energy grant supporting the U’s geothermal research station known as Utah FORGE.

Read the full story by Brian Maffly in @TheU