Earthquakes

Division of Emergency Management

Earthquakes

An earthquake happens when two blocks of the earth suddenly slide past each other along a crack called a fault. Over time, pressure builds up in the ground from the movement of Earth's plates and other natural forces. When this pressure becomes too great, the fault suddenly slips and releases the stored energy as waves that spread out through the rock in all directions, causing the ground to shake.

Utah sits away from the major plate boundaries where most of the world's earthquakes happen. Instead, Utah is in the middle of the North American plate. However, forces from the Pacific plate along the West Coast still affect Utah, causing stress that can trigger earthquakes here.

Earthquakes can cause widespread damage and loss of life in multiple ways beyond just ground shaking.

Direct earthquake effects include:

Cracks in the ground along faults
Soil liquefaction (when saturated ground loses strength and behaves like liquid)
Landslides and rockfalls
Ground sinking or shifting

Damage from ground shaking can cause:

Buildings and roads to collapse or crack
Fires from broken gas lines
Dam and canal failures leading to flooding
Hazardous material spills from damaged facilities
Indoor damage like toppled furniture, bookcases, and cabinets
Falling ceiling tiles, light fixtures, and equipment
Broken water and power lines

Utah sits between two geological regions: the Basin and Range to the west (where the earth's crust is stretching) and the more stable Rocky Mountains and Colorado Plateau to the east. This boundary area experiences frequent earthquake activity in a zone called the Intermountain Seismic Belt.

The Intermountain Seismic Belt is up to 120 miles wide and runs 800 miles from Canada through Utah to northern Arizona and eastern Nevada. In Utah, this earthquake zone runs through the center of the state, roughly following Interstate 15, where many active faults can produce earthquakes.

More than 85% of Utah's population lives in this earthquake zone along the Wasatch Front, including the rapidly growing St. George and Cedar City areas.

Utah's earthquake history: Earthquakes of magnitude 6 or larger can cause serious damage to buildings, roads, bridges, and utilities, leading to injuries and deaths. Utah has experienced several significant earthquakes:

1934: A magnitude 6.6 earthquake near Hansel Valley caused ground rupture and killed two people—Utah's only historical earthquake to break the ground surface
1975: A magnitude 6.0 earthquake in Pocatello Valley, Idaho, affected northern Utah

Mitigation Case Study: Fix The Bricks Program

damaged side of a brick building from an earthquake with debris on the ground

Along the Wasatch fault, there are estimated to be over 140,000 unreinforced masonry (URM) structures. The devastating potential of the Wasatch Fault is due in part to its proximity to Utah’s most densely populated areas. Many Utahns work, study, and live in unreinforced masonry (URM) buildings, heightening the danger of collapsed buildings after an earthquake. The Fix the Bricks program aims to fund 75% of the retrofit of URM homes in Salt Lake City.

Salt Lake City partnered with the State of Utah to apply and receive funding for this project under FEMA's Legacy Pre-Disaster Mitigation program. The pilot 2016 grant of over $700,000 funded the retrofit of 29 homes, while a 2019 grant of more than $5 million aims to retrofit another 200 homes.

For more resources and information on earthquakes in Utah, please visit earthquakes.utah.gov

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