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One year later: Over 2,500 aftershocks recorded since 5.7 Magna earthquake



Thursday marks one year since a 5.7 earthquake struck northern Utah near Magna, shaking the ground and waking people in the surrounding areas.

Since it struck the Wasatch Front, the sequences has give scientists more information about future earthquakes. Most importantly, that ground shaking may be higher than previously thought because of the fault’s shallower depth.

On Wednesday, March 17, the mainshock was widely felt across the Wasatch Front around 7 a.m. Prior to the shaking, six magnitude 3.0 or larger earthquakes have occurred in the area since 1962; the largest was a magnitude 5.2 in 1962.

Utah is at risk of a major earthquake of magnitude 7 to 7.5, and the 5.7 Magna earthquake did not diminish that risk, experts warn.

The earthquake sequence is still ongoing, but has seen a decrease in activity over the last year.

Over 2,500 aftershocks have been recorded as part of that sequence, according to a report released by state agencies. These included one in the magnitude 5 – 5.9 range; six in the magnitude 4 – 4.9 range; 30 in the magnitude 3 – 3.9 range; 137 in the magnitude 2 – 2.9 range; 698 in the magnitude 1 – 1.9 range; 1,507 in the magnitude 0 – 0.9 range and 83 less than magnitude 0.

There were also 28 earthquakes where no magnitude could be determined.

No major injuries were reported during the mainshock or aftershocks. But, they did cause severe damage, mostly in Magna near the epicenter.

HAZUS, software used by the state to estimate potential losses, shows there could be upwards of $62 million in building-related damages, contributing to $629 million in total economic loss. This does not include damages to public infrastructure, according to the report by the state.

“The Magna earthquake sequence is one of the best recorded earthquake sequences in the entire Basin and Range province,” Keith Koper, director of UUSS and chair of the Utah Seismic Safety Commission (USSC), stated in a news release.

Our network of permanent and temporary seismometers created a wealth of data that led to several research opportunities both published and ongoing. This research has impacted our understanding about faults, earthquakes, and seismic hazard in Utah and the Intermountain West.

Before this 5.7 earthquake, scientists did not know the exact location of the Wasatch fault. They previously thought it dipped at a steep angle deep beneath the Salt Lake Valley.

Based on the data from this earthquake sequence, several research papers now suggest the sequence occurred on the Salt Lake City segment of the Wasatch fault. Evidence suggests the fault curves to a shallower angle and is not as deep beneath the surface as previously thought.

Because of this, ground shaking estimates may be higher than previously thought for future earthquakes on the Salt Lake City segment of the Wasatch fault, state agencies reported. They suggest ground-motion scenarios for future earthquakes should be reevaluated to account for increased shaking.

The magnitude 5.7 was a moderate earthquake and a reminder that Utah is earthquake country.

Utahns can reduce their risk in an earthquake by being prepared beforehand. Remember to drop, cover and hold on during an earthquake. State agencies suggest having a minimum of a two-week supply of water, food, medicine and other necessities. Also, be prepared for long disruptions to utilities like power, water and sewer. Learn more here.

You can also register to participate in the Great Utah ShakeOut on April 15, 2021.

The University of Utah Seismograph Stations, Utah Geological Survey, Utah Department of Public Safety, and the Utah Division of Emergency Management were state agencies involved in gathering the information for this report.

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