An earthquake occurs when two blocks of the earth suddenly slip past one another, releasing
built up energy from plate tectonics, regional stress regimes, and induced from fluid injection or
underground mining activities. The surface between these two blocks is called a fault or fault
plane. When these blocks move, they produce seismic waves that are transmitted outward
through the rock in all directions, producing ground shaking and secondary effects. Utah is
situated away from the primary tectonic plate boundaries where a significant portion of the
world’s earthquakes typically occur. Instead, it lies within the western portion of the North
American plate. Nevertheless, seismic activity in Utah is ultimately influenced by its connection
with the Pacific plate, primarily along the plate’s edge along the west coast of the United States.

Earthquakes are unique multi-hazard events with the potential to cause excessive damage and
loss of life. Earthquake secondary effects often include surface fault rupture (generally≥
magnitude [M] 6.5), liquefaction and lateral spreading can be triggered as low as approximately
0.1 g.4 Landslides, rock fall (generally ≥ M 4), tectonic subsidence, seiches and tsunamis. Effects
from ground shaking may include building and infrastructure damage, fires, building, dam and
canal failure, hazardous material releases, and non-structural building damage such as toppled
cabinets, bookcases, and other furniture or equipment that was not restrained, falling ceiling
tiles, lights, and other ceiling mounted items, and movement of unrestrained furniture,
equipment, and other building interior items.

Utah straddles the physiographic region boundary between the extending Basin and Range
Province to the west and the relatively stable Rocky Mountains and the Colorado Plateau to the
east. This boundary coincides with an area of earthquake activity called the Intermountain
Seismic Belt (ISB). The ISB is a zone of significant earthquake activity up to 120 miles wide
extending in north-south direction 800 miles from Canada to northern Arizona and eastern
Nevada. Large, damage-causing earthquakes in Utah are likely to occur in the ISB that generally
extends through the center of the state, essentially following Interstate 15, where there are many
active faults capable of producing earthquakes. Unfortunately, this location is also where over
85% of Utah’s population lives along the Wasatch Front, and also includes the rapidly urbanizing
St. George and Cedar City areas.

Moderate-to-large earthquakes, generally M 6 and greater, can cause substantial damage to
buildings, roads, bridges, and utilities often leading to injuries and fatalities. Background
earthquakes are defined as those events less than M 6.75 ± 0.25 that cannot be associated with
a known fault. A classic example of a background earthquake within the Wasatch Front region
is the 1975 M 6.0 Pocatello Valley, Idaho, earthquake. Utah’s only historical surface fault rupturing
earthquake is the 1934 M 6.6 Hansel Valley earthquake that also caused two fatalities.ground shaking, sound, extreme weather, human, or animal movement. Avalanches consist of a
starting zone where the ice or snow breaks loose, a track, which is the grade or channel the
debris slides down and a run-out zone where the snow is deposited.

Since the 2019 plan, Utah has had numerous avalanches. Avalanches are one of the deadliest
types of natural disasters in Utah. According to the National Oceanic and Atmospheric
Administration’s (NOAA) National Centers for Environmental Information (NCEI) database,
between 1996 and 2022, avalanches have caused 128 deaths in the state accounting for 70% of
severe weather-related deaths.

An avalanche is a mass of snow, ice, and debris sliding rapidly down steep slopes. Snow
avalanches occur in the mountains of Utah during the winter and spring seasons as a result of
snow accumulation and unstable snowpack conditions. January through April avalanche risks
are the highest in Utah where they pose a significant mountain hazard. Annually, avalanches
account for more deaths than earthquakes in the US. Determining the probability of an
avalanche occurring can help save money and protect human life.