A significant seismic event struck the greater Salt Lake City area in 2020, serving as a powerful reminder of the region’s underlying geological activity. This tremor impacted the densely populated Wasatch Front, causing widespread shaking and immediate disruptions across northern Utah. The event initiated a long sequence of smaller movements. Understanding the specifics of this earthquake requires examining its measurements, geological context, and the resulting human experience.
The Main Shock: Magnitude and Location
The earthquake registered an official moment magnitude of 5.7. It occurred on March 18, 2020, at 7:09 a.m. Mountain Daylight Time, with an epicenter approximately six kilometers north-northeast of Magna, Utah, a suburb of Salt Lake City. The hypocenter was relatively shallow, measured at a depth of about 11.9 kilometers (7.4 miles) beneath the surface.
This magnitude 5.7 event was the strongest to affect the Salt Lake Valley since the city’s founding in 1847 and the largest recorded in the state since a magnitude 5.9 quake struck St. George in 1992. The energy released was substantial enough to produce intense shaking, reaching a Modified Mercalli Intensity of VII in the epicenter area. The quake’s location and strength provided seismologists with new data on the area’s fault mechanics, prompting a re-evaluation of the local seismic hazard.
Understanding the Wasatch Fault Zone
Utah’s seismic risk lies in the Wasatch Fault Zone (WFZ), a 390-kilometer-long normal fault running along the western base of the Wasatch Mountains. This fault system marks the boundary between the rising mountains to the east and the subsiding Great Basin to the west. The WFZ is segmented, and the 2020 event occurred on a structure associated with the Salt Lake City segment.
The Wasatch Fault is considered one of the most active normal faults in the world. Paleoseismic studies show that major surface-rupturing earthquakes, potentially reaching magnitude 7.0 or greater, occur roughly every 900 to 1,300 years along any one of the five most active segments. Research following the 2020 Magna earthquake suggested that the fault structure beneath the Salt Lake Valley may have a shallower dip than previously estimated, which could amplify future ground shaking during a larger event.
The Aftershock Sequence
Following the main shock, the region experienced a prolonged sequence of aftershocks, which are smaller earthquakes caused by the crust adjusting to the sudden release of stress. The University of Utah Seismograph Stations recorded over 2,590 aftershocks in the months following the initial event. This extended sequence followed a typical pattern, though it included several events large enough to be felt widely.
The most significant aftershocks occurred on the same day as the main shock, with two separate events registering a magnitude of 4.6. The continued shaking, including dozens of events of magnitude 3.0 or greater, lasted for weeks and months, unsettling residents. Seismologists tracked the aftershocks to two main groupings, providing valuable insights into the subsurface fault connections.
Immediate Impact and Community Response
The 5.7 magnitude tremor caused widespread but mostly moderate physical damage, concentrated primarily in the Magna area and Salt Lake City. Initial reports indicated no fatalities, but several minor injuries were reported. Structural damage was visible on older buildings, and the historic Salt Lake Temple sustained damage, notably losing the trumpet from the Angel Moroni statue atop its spire.
The earthquake immediately disrupted essential services, with power outages affecting up to 73,000 customers across northern Utah. The Salt Lake City International Airport was temporarily evacuated and closed, and the TRAX light rail system was halted for safety inspections. The response was complicated because the state was in the early stages of the COVID-19 pandemic, requiring emergency management officials to balance earthquake protocols with public health measures. This timing meant many offices and schools were already operating remotely, inadvertently reducing the number of people in vulnerable structures.