Why is earthquake preparedness important in Utah?
Utah has experienced damaging earthquakes in the past and geologic evidence indicates that much larger earthquakes are likely in the future.
Utah must prepare for earthquakes because:
- Utah is earthquake country. It is in a seismically active region.
- A majority of Utah’s population is concentrated in the areas of greatest hazard.
- Many of Utah’s older buildings and critical infrastructure have low earthquake resistance.
Unreinforced Masonry Buildings
Most of Utah’s unreinforced and lightly reinforced brick, stone, and block buildings were built prior to 1975. Such buildings were commonly constructed using solid masonry load-bearing walls without adequate steel reinforcing. As a result, these buildings can be brittle and suffer damage or collapse during moderate to large earthquakes. Furthermore, such buildings commonly lack proper attachment between the walls and roof, preventing the roof from stabilizing the walls, further contributing to their structural weakness during an earthquake.
The Utah State Historic Preservation Office can assist homeowners and communities with the seismic retrofit and repair of historic buildings through Federal and State Historic Tax Credit programs, grants provided under the Certified Local Government program, and the professional technical assistance of their Historical Architect. Preservation Utah also helps find resources to preserve old buildings and homes through a variety of loans and grants. The Salt Lake City Fix the Bricks program provides assistance to Salt Lake City homeowners with the costs of seismic structural improvements to their unreinforced masonry homes.
Frequently Asked Questions
Geology of Earthquakes in Utah
Utah has experienced seventeen earthquakes greater than magnitude 5.5 since pioneer settlement in 1847, and geologic studies of Utah’s faults indicate a long history of repeated large earthquakes of magnitude 6.5 and greater prior to settlement. Utah is not on a boundary between tectonic plates where most of the world’s earthquakes occur, but rather is in the western part of the North American plate. However, earthquakes in Utah are related to interactions with the Pacific plate along the plate margin on the west coast of the United States.
There is a 57% probability that the Wasatch Front region will experience at least one magnitude 6.0 or greater earthquake and a 43% probability of at least one magnitude 6.75 or greater earthquake in the next 50 years.
Stretching, or horizontal extension, of the crust produces a type of dipping (or inclined) fault called a “normal” fault. The movement of normal faults is characterized by the crust above the fault plane moving down relative to the crust below the fault plane. This up/down movement differs from movement on strike-slip faults like the San Andreas in California, where the crust on one side of the fault slides horizontally past the crust on the other side. Putting Down Roots in Earthquake Country
Large Earthquakes on the Wasatch Fault
Click to explore a Story Map timeline of large (magnitude 6.5 and greater) earthquakes on the Wasatch fault
MYTH: Utah can have a magnitude 9.0 earthquake
Earthquakes greater than about magnitude 7.6 are not possible from the Wasatch fault zone or other faults in Utah. Faults in Utah are not long enough and are a different type than those off the coast of Alaska, Washington State, and the west coast of South America (Chile area), where earthquakes of magnitude 8 or greater are possible.
MYTH: Triangle of Life
According to the United States Geological Survey (USGS), the Triangle of Life is a misguided idea about the best location a person should try to occupy during an earthquake. It is actually very difficult to know where these triangles will be formed, as objects (including large, heavy objects) often move around during earthquakes. This movement means that lying beside heavy objects is very dangerous. Statistical studies of earthquake deaths show most injuries and deaths occur due to falling objects, not structures. According to the American Red Cross, Drop, Cover, and Hold On under a table or desk is still the best recommendation.
- Video of ground shaking from the Magna Earthquake 2020
- Damage in downtown Magna from the Magna Earthquake 2020
- Damage to a home from a generated landslide from the Washington County 1992 M5.9 earthquake
- Damage to a basement from a generated landslide from the Washington County 1992 M5.9 earthquake
- Damage to a garage from the 1962 Cache Valley earthquake
- Hansel Valley, 1934. The ground was displaced .5 meters (1.5 ft). This is the only historic surface rupturing earthquake event in Utah.