Fault Lines
Every fault the Utah Geological Survey has mapped as active in the last 2.6 million years. Tap a fault to learn about it, or tap anywhere else to look up that spot. Use the map key to switch layers on and off.
The Wasatch fault in a minute
The Wasatch fault zone runs about 220 miles from Malad City, Idaho, to Fayette, Utah. It's a normal fault: the valley drops down and the mountains rise, a few meters at a time, in large earthquakes thousands of years apart. That's how the Wasatch Range got so tall and the valleys so deep.
The fault breaks in pieces called sections, each of which tends to rupture on its own. The six central sections show repeated large earthquakes in the last several thousand years:
| Section | Runs along |
|---|---|
| Brigham City | Brigham City to near Ogden |
| Weber | Ogden, Layton, Bountiful area |
| Salt Lake City | The east bench of the Salt Lake Valley, from North Salt Lake to Draper |
| Provo | Utah Valley, from Alpine to Spanish Fork and Payson |
| Nephi | Santaquin to Nephi |
| Levan | South of Nephi |
Section names and extents follow the Utah Geological Survey's Quaternary Fault and Fold Database. Community descriptions are approximate; tap the map for the mapped trace.
Not just the Wasatch
The West Valley fault zone (the Granger and Taylorsville faults) cuts across the middle of the Salt Lake Valley and likely moves together with the Salt Lake City section. Utah's largest recorded earthquake, a magnitude 6.6 in 1934 in Hansel Valley, north of the Great Salt Lake, broke the ground surface. Southern Utah has its own active faults, including the Hurricane fault.
How often does the ground break?
Only large earthquakes, about magnitude 6.5 and up, break the ground surface. When they do, the fault scarp (a sudden step in the ground) can be from a few inches to 20 feet high and up to about 40 miles long. Damage concentrates in a zone hundreds of feet wide, mostly on the downdropped valley side. Utilities and roads that cross the fault can be cut.
On average, the Utah Geological Survey estimates such an earthquake strikes:
- About once every 120 years somewhere in the Wasatch Front region
- About once every 350 years somewhere along the central Wasatch fault, between Brigham City and Nephi
- About once every 2,000 years at any one spot along the central Wasatch fault
That's why the fault study zones on the map matter: they mark where a geologic study is recommended before building.
Utah Geological Survey, Utah Faults.
Magna on the map
Switch on Magna 2020 shaking in the map key to see how strongly the 2020 magnitude 5.7 earthquake shook across the valley, from the USGS ShakeMap. The orange dot is the epicenter. Read the Magna story.
Reading the colors
Faults are colored by how recently they've moved. Red faults have moved in the last 15,000 years, which in geologic time is yesterday. Those are the ones scientists watch most closely. An older fault isn't necessarily safe; it may just have a longer gap between earthquakes, or less study.