Of all the geologic hazards present in Utah, earthquakes pose the greatest threat to human life and structural damage from a single event. The Wasatch fault zone is the longest and most active fault in the region, extending 240 miles from north of Malad City, Idaho, to near Fayette, Utah, but there are hundreds of other hazardous faults across the state that have the potential to generate large earthquakes.
Ground shaking is the most widespread earthquake hazard and typically causes the most damage, but other potential earthquake hazards include surface faulting, liquefaction, and earthquake-induced landslides and flooding.
Surface faulting occurs during large earthquakes (generally magnitude 6.5 or greater) when the fault rupture reaches the ground surface and creates a fault scarp (a vertical break or offset). Generally, homes that straddle or are very close to fault lines have the greatest risk of damage from surface faulting.
Liquefaction may occur when loose, water-saturated, sandy soil is subjected to strong ground shaking and the soil behaves more like a liquid than a solid, which can cause houses to settle or tilt. Liquefaction potential is typically higher on valley floors and near streams and other water bodies. Landslides (and especially rockfalls) can be triggered by ground shaking, and flooding can result from dam failure, stream obstruction, water-line or canal breaks, and tilting (subsidence) of the land near water bodies.