Wasatch Fault: Earthquake Risk, History & Live Activity
The Wasatch Fault is a normal fault running about 380 kilometres along the base of the Wasatch Range in Utah, through the populous corridor that includes Salt Lake City, Provo, and Ogden. It is not a plate-boundary fault but an extensional feature where the crust of the Basin and Range province is slowly pulling apart, dropping the valleys down relative to the mountains at a long-term rate of about 1 to 2 millimetres a year. The fault is divided into segments that rupture independently.
How likely is a large earthquake?
The Working Group on Utah Earthquake Probabilities (2016) estimated a 43 percent chance of a magnitude 6.75 or larger earthquake somewhere in the Wasatch Front region over 50 years, and a 57 percent chance of a magnitude 6 or larger. The Salt Lake City segment is among those judged highest-risk because it has gone the longest without a major rupture.
Paleoseismic trenching indicates that large earthquakes on the Salt Lake City segment have recurred on average roughly every 1,300 years, and the most recent was about 1,400 years ago. That the elapsed time slightly exceeds the average is one reason the segment draws attention, though, as always, an average is not a schedule.
Live seismic activity near this fault
Counts include M2.5+ events — the smallest size USGS reports consistently worldwide.
| Magnitude | Time (UTC) | Depth | Location |
|---|---|---|---|
| M3.3 | Jul 25, 20:32 UTC | -2 km | 2 km NW of Little America, Wyoming |
| M3.2 | Jul 23, 03:12 UTC | 5 km | 6 km WSW of Bennington, Idaho |
| M3.0 | Jul 22, 06:09 UTC | -2 km | 6 km WSW of Bennington, Idaho |
History
Utah's largest earthquakes in the geologic record are prehistoric surface-rupturing events on the Wasatch Fault; the historical instrumental record is more modest.
- Prehistoric segment ruptures (estimated M6.5 to 7.5) — trenching documents repeated large earthquakes over the past several thousand years, the most recent on the Salt Lake City segment about 1,400 years ago.
- 1934 Hansel Valley (M6.6) — Utah's largest historical earthquake, north of the Great Salt Lake and off the main Wasatch Fault.
- 2020 Magna (M5.7) — the strongest earthquake near Salt Lake City in decades, consistent with movement on the Wasatch fault system.
Frequently asked questions
Is the Wasatch Fault overdue?
The Salt Lake City segment last produced a major earthquake roughly 1,400 years ago, slightly longer than its estimated average interval of about 1,300 years, so it is sometimes described as near or just past due. That is a statement about long-term averages drawn from trenching, not a prediction of timing. Utah has never recorded one of these large segment-rupturing earthquakes in its written history.
What would a big Wasatch earthquake do?
State scenarios for a magnitude 7 on the Salt Lake City segment project strong shaking across the Wasatch Front, amplified by the soft valley sediments beneath many communities, along with surface faulting and liquefaction near the fault. Much of the older building stock predates modern seismic codes, which is the main driver of the projected damage.
Nearby regions
Live counts from the USGS earthquake feeds within 200 km of the fault. Magnitudes and depths are automated readings and may be revised. Not for emergency use.