Utah’s Wasatch Fault is overdue for the quake that could flatten Salt Lake City

A magnitude-7.0 earthquake on the Salt Lake City segment of Utah’s Wasatch Fault could kill an estimated 2,000 to 2,500 people and cause more than $33 billion in direct losses, according to a scenario study built for the state’s own seismic safety commission. The segment capable of producing that earthquake last ruptured somewhere between 1,200 and 1,600 years ago, and segments like it typically break every 900 to 1,300 years.

New research published in 2025 suggests the fault is also shaped in a way that could make surface shaking worse than older models assumed. Utah has had the loss estimate for over a decade and has only begun chipping away at the buildings the estimate says will fail.

The Segment That’s Already Overdue

The Wasatch Fault is not a single fracture but ten linked segments running roughly 220 miles from near Fayette in central Utah north to Malad City, Idaho. The five central segments, including the one that runs beneath Salt Lake City, produce magnitude-7-scale earthquakes on a rough cycle the U.S. Geological Survey puts at every 900 to 1,300 years. The Salt Lake City segment’s most recent rupture happened 1,200 to 1,600 years ago, which places it at or past the interval that has historically preceded the next one. Trenches cut across the fault zone have documented at least 22 surface-faulting earthquakes in just the past 6,000 years.

That geologic clock sits directly under the fastest-growing metro corridor in the state. USGS notes the active strands of the Wasatch fault zone run adjacent to the largest and still-growing population centers along the Wasatch Front, a description written by geologists, not real-estate marketers.

New Research Says the Shaking Could Be Worse

A study published online in April 2025 in the journal Geology, led by Utah State University geoscientists Srisharan Shreedharan, Alexis Ault and doctoral student Jordan Jensen, found that the Wasatch Fault likely curves more gently at depth than earthquake models had assumed, and that the rock along that shallower plane is unusually weak and slick — a texture the researchers trace to deformation that began 1.7 billion years ago and has been ground smoother by repeated quakes since. A shallower, slicker fault plane changes how energy reaches the surface. Shreedharan put it directly: “This means that an earthquake rupture could lead to stronger, more intense shaking at the surface — meaning a greater chance of injury and destruction.”

The research team pointed to the March 2020 magnitude-5.7 Magna earthquake, centered about 9 kilometers underground west of Salt Lake City, as a preview even at a fraction of the scale under discussion. Magna caused injuries and roughly $50 million in property damage. A magnitude-7.0 rupture on the segment beneath the city would release dramatically more energy than that event, on a fault the new study says is arranged to transmit that energy to the surface especially efficiently.

What a Full Scenario Would Cost, in Deaths and Dollars

The most detailed public accounting of what such an earthquake would do to Salt Lake City itself comes from a 2015 scenario report the Earthquake Engineering Research Institute’s Utah Chapter prepared for the Utah Seismic Safety Commission. It modeled a magnitude-7.0 rupture on the Salt Lake City segment and put the toll at 2,000 to 2,500 deaths and 7,400 to 9,300 people needing hospital care, depending on the time of day the ground moves.

The property numbers are just as specific. The report counts 308,100 structures affected across four damage tiers, from 125,500 with slight damage to 55,400 destroyed outright, for a combined $33.2 billion in losses — $24.9 billion in building damage, $6.9 billion in lost income, and $1.4 billion to lifelines like water and power. It projects 84,400 households, roughly 263,300 people, displaced from their homes, with 52,700 of them needing emergency shelter, and about 21 million tons of debris requiring more than 821,600 truckloads to haul away.

The Buildings Regulators Haven’t Gotten to Yet

Much of that projected toll traces to one building type. A Wasatch Front risk strategy prepared for FEMA counts more than 140,000 unreinforced masonry buildings across the corridor, nearly all built before Utah banned the construction method in the 1970s. Unreinforced masonry is exactly the kind of structure that performs worst in strong shaking — brick and block walls with no steel frame to hold them together — and it is the building stock the 2015 scenario’s casualty numbers lean on most heavily.

Progress is visible, if slow. A statewide school-building inventory released in 2022, funded by FEMA and built with all 41 Utah public school districts, found unreinforced masonry construction had dropped from roughly 95% of the state’s schools 60 years earlier to about 12% at 119 remaining campuses. Kris Hamlet, director of the Utah Division of Emergency Management, said at the time that publishing the list itself was part of the fix: “This transparency will help unite communities and identify resources to fix or replace remaining buildings.”

The Utah Geological Survey continues to update the hazard maps that track liquefaction zones and mapped fault traces across the valley floor, the data retrofitting decisions are supposed to be built around. Retrofitting the roughly 140,000 masonry buildings outside that school inventory has no announced completion date, and the segment the 2015 scenario was built on has not moved since before any of those buildings, or the cities around them, existed.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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