Earthquakes are caused by a sudden movement of the earth along a fault. As the rocks on either side of the fault accumulate stress between them, they will eventually overcome friction and slip. The resulting earthquake releases energy in waves that travel through the Earth’s crust. These waves can cause noticeable shaking at the surface and, in the case of large earthquakes, damage to roads, buildings, and other infrastructure that may pose a threat to public safety.
Colorado is considered an active tectonic province that is essentially being pulled apart where the Rio Grande Rift cuts north/south across the mountainous, central part of the state. Colorado’s high mountains are a result of uplift on faults (with associated earthquakes) that are part of the rift system. The active landscape of the state — with the still-rising mountains containing thousands of faults — features over 90 potentially active faults and more than 700 recorded earthquakes of magnitude 2.5 or higher since 1867. Colorado experiences fewer and less frequent earthquakes on average than more seismically active states like California. However, the state has experienced large natural (magnitude 6.5 or higher) and human-triggered (induced) earthquakes in recorded history and will continue to periodically experience large earthquakes in the future.
Earthquake hazard is the likelihood of a certain level of shaking, also known as “Peak Ground Acceleration,” that may occur from an earthquake in a particular area. Colorado has low-to-moderate earthquake hazard as rated by the U.S. Geological Survey Earthquake Hazards Program. Earthquake risk is the likelihood of economic or personal loss occurring from an earthquake in a particular area, and is determined by looking at the level of earthquake hazard, the number of people and properties in the hazard area, and the vulnerability of people and infrastructure to earthquakes. Knowledge of both hazards and risk are vitally important in the resilience planning for earthquake events.
Earthquakes can cause damage to buildings and infrastructure directly through shaking, but they are sometimes also responsible for causing related hazards, such as ground fissures, soil liquefaction, landslides and rockfalls, and more. In order to reduce risks from earthquake-associated hazards, it is important to study local geology and soil conditions.