Colorado experiences earthquakes, though less frequent and powerful than in highly active regions like California or Alaska. Many tremors are minor and often go unnoticed. Understanding Colorado’s seismic activity is practical for residents. This article explores the patterns, geological reasons, historical events, and preparedness steps for earthquakes in Colorado.
Earthquake Frequency and Magnitude in Colorado
Colorado’s seismic activity includes consistent smaller tremors. Since 1867, the state has recorded over 700 earthquakes with a magnitude of 2.5 or higher. Annually, Colorado experiences approximately 58 earthquakes of magnitude two or higher, with about nine reaching magnitude three or higher. The majority of these events are quite minor, often going unnoticed by humans and only detectable by sensitive seismic instruments.
The U.S. Geological Survey classifies the overall earthquake hazard in Colorado as low to moderate. This indicates a general pattern of frequent, low-magnitude events rather than powerful, destructive ones. For instance, in the past 10 years, no earthquakes with a magnitude of 5 or above have occurred within a 300-kilometer range of Colorado.
Geological Reasons for Colorado Earthquakes
Earthquakes in Colorado stem from the movement along ancient fault lines within the Earth’s crust. The state is considered an active tectonic province, where the crust is slowly stretching and thinning. This process is particularly evident along the Rio Grande Rift, which cuts north-south through the central, mountainous part of the state, contributing to uplift and associated faulting.
Colorado contains thousands of faults, with around 90 identified as potentially active within the last 1.6 million years. Notable fault systems include the Front Range, Sangre de Cristo, Sawatch, Cheraw, Gore Range, and Rampart Range faults. These faults can reactivate due to regional tectonic stresses, which involve extension along a roughly northeast-oriented axis.
Human activities can also induce seismicity in Colorado. Deep underground injection of wastewater, often from oil and gas operations, can increase pore pressure in rocks, effectively reducing friction on faults and triggering earthquakes. This phenomenon has been observed in areas like the Raton Basin and near Greeley, where increased fluid injection has correlated with a rise in seismic events.
Notable Earthquakes and Their Impact
Colorado’s seismic history includes several events that illustrate the potential for shaking and damage. The largest known earthquake occurred on November 7, 1882, with an estimated magnitude of 6.6. Centered near the Front Range, west of Fort Collins, this event caused damage in Denver, including cracked buildings in Boulder and damage to a power plant.
Another significant event was the magnitude 5.3 earthquake on August 9, 1967, centered near Commerce City in the Denver metropolitan area. This tremor caused over $1 million in damages, primarily in Northglenn, where concrete supports of a church were weakened and numerous windows were broken. Many homeowners reported cracks in walls, ceilings, and foundations. This particular earthquake is believed to have been induced by the deep injection of liquid waste at the Rocky Mountain Arsenal.
More recently, a magnitude 5.3 earthquake struck on August 23, 2011, near Segundo and Valdez in southern Colorado, causing moderate damage. While major damaging earthquakes are rare, these historical events demonstrate that Colorado is not immune to seismic activity that can affect populated areas and infrastructure.
Preparing for Earthquakes in Colorado
Even though major earthquakes are infrequent in Colorado, preparedness remains a practical approach for residents. A widely recommended safety action during shaking is “Drop, Cover, and Hold On.” This involves dropping to your hands and knees, covering your head and neck under sturdy furniture, and holding on until the shaking stops.
Securing heavy furniture, such as bookcases and water heaters, is another important step to prevent them from tipping over during an earthquake. Moving heavier objects to lower shelves can also minimize hazards. Creating an emergency kit with supplies for at least three days, including water, food, and a first-aid kit, is advisable.
Developing a family emergency plan, including designated meeting points and an out-of-area contact, ensures communication and safety if separated. Practicing earthquake drills, like the “Drop, Cover, and Hold On” method, helps ensure a swift and appropriate response when an event occurs.