The Geography of Northern Utah: The Wasatch Fault Line

It is surprising to many people that Utah, of all places, has earthquakes that range from mild to moderate (up to a magnitude of 7.5!). But according to geology.utah.gov there are hundreds of small earthquakes reported in Utah each year; these earthquakes tend to have a magnitude of about 5.5-6.5. So while these may seem small to many people, they are still big enough to do some damage. In fact, Utah is commonly known to be the highest risk of earthquakes in the interior of the western United States. Now these earthquakes may not be very large, but they bring such a high risk but many of Utah’s most populated areas happen to be along the Wasatch Basin, a mountain range in Utah that, for the most part, runs along a large fault line: the Wasatch fault. 80% of Utah's population actually resides along the fault line itself.

The Wasatch Fault Line is a Normal Fault, and it runs through the center of Utah

There Wasatch Fault Line has been separated into ten segments. A few of them can be seen here.

The Intermountain seismic belt can be found on the interior of the North American plate; it is about 800 miles long, and runs from Montana all the way down to the top of Arizona and the edge of Nevada. Within this belt we find the Wasatch fault, which extends from the bottom of Idaho all the way down to the bottom/central portion of Utah.

Earthquakes are a result of fault movements, so every time the Wasatch fault decides to move even just a little bit, anything nearby has the chance of being affected. This earthquakes leave behind footprints; the most common footprint that we can see along the Wasatch Basin are scarps and grabens. A "scarp" to the naked eye looks like a line of cliffs along a mountain, but these almost always signal that a fault is nearby; a true scarp is formed by the vertical thrusting of the Earth’s crusts. A graben, however, is similar to a valley. Grabens sink in due to fault movements and are usually surrounded by horsts (crust that is being compressed and pushed upwards). The Wasatch Basin contains a lot of escparment (scarps) and a lot of grabens, indicating that there has been a lot of earthquake activity, whether it has been recent or in the distant past.