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ON-001 Colorado Earthquake and Fault Map

Earthquakes

Think you just felt an earthquake??

Check out the USGS Latest Earthquakes Map.

Earthquakes are caused by sudden movements 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 and Alaska. 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.

Faults

Because fault movement causes earthquakes, it is important to study the thousands of faults in Colorado to determine whether they have moved in the recent geologic past or capable of moving again in the near future. The CGS conducts scientific studies of fault zones and past earthquakes while monitoring fault movements with a network of seismometers throughout Colorado.

Twelve faults in Colorado have received sufficient study to be included in the USGS National Seismic (Earthquake) Hazard Map (version 2023 NSHM), and are listed as being capable of generating earthquakes of 7.0 magnitude, or greater. There are many more faults in the state that could probably generate significant earthquakes, but have not received sufficient study, or documentation, to be included in the hazard map. With our current state of knowledge, it is not possible to predict when or where, the next large earthquake might occur in Colorado.

Earthquake Size

Earthquakes are measured in several ways: magnitude, intensity, and ground acceleration.

Magnitude is determined by measurements of recordings on seismographs. Hypothetically, all seismographs around the world should yield the same magnitude for a given earthquake, no matter the distance from the epicenter. Magnitude is always presented in numerals. There are a number of different methods for calculating magnitude: Moment Magnitude, Richter Magnitude, Rayleigh Surface Wave Magnitude, and Gutenberg Body Wave Magnitude. Colorado did not have seismographs prior to 1900, nor did many parts of the U.S. so for older earthquakes we can only estimate their magnitudes from their intensity.

Intensity estimates are based on what people observe or feel during an earthquake. Intensity varies with distance from the fault, and depends on soil conditions and/or height one is in a building when the shaking occurs. Intensity is always presented in Roman numerals. There are methods for plotting up the intensities in different places and deriving an estimated magnitude from the distribution. The magnitude of 6.6 for the earthquake of 1882 that had its epicenter in north-central Colorado was derived in this manner.

Ground acceleration is measured as a percentage of the force of gravity by strong motion instruments. They are also what the National Earthquake Hazard Maps use in their hazard assessment. Like intensities, ground accelerations vary according to distance from the fault, soil conditions, and type of structure. Ground acceleration values are used in designing earthquake resistant structures. Colorado does not have any buildings instrumented to measure strong motion.

The USGS hosts a detailed discussion of Earthquake Magnitude, Energy Release, and Shaking Intensity for further information.

Hazards

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.

Colorado Division of Homeland Security and Emergency Management – EarthquakesInformation on earthquake preparedness, Colorado earthquake hazards, and additional preparedness resources.

Colorado EarthquakesYouTube video about Colorado earthquakes.

Induced Earthquake BibliographyThis comprehensive bibliography contains several hundred references concerning human-induced earthquakes and other seismicity.

Denver Basin Earthquake StudiesInduced seismicity project covering Weld County, Colorado by researcher Anne Sheehan at the Cooperative Institute for Research in Environmental Sciences (CIRES), CU-Boulder.

Federal Emergency Management Agency EarthquakesFederal earthquake hazard maps, federal funding for risk management and building codes.

The Great ShakeOutInformation on the annual nationwide earthquake drill, drill procedures, and tips for earthquake preparedness.

USGS Hazards Program – ColoradoColorado seismicity, hazard maps, and Colorado-specific earthquake topics.

USGS Earthquake Hazards ProgramInformation on faults, hazard maps, and earthquake ground motion.

USGS Earthquake Notification ServiceA customizable service for receiving timely notifications about any earthquakes — national and international.

Western States Seismic Policy Council (WSSPC) — A non-profit earthquake consortium for western US states

HAZUS simulation: 1882 Earthquake, Rocky Mountain National Park Epicenter M 6.6, CEUS Attenuation

The Earthquake Reference Collection

The Earthquake Reference Collection (ERC) is a comprehensive library of Colorado-specific reports, maps, documents, and papers examining the geoscience behind earthquakes and faulting around the state. The CGS assembled the collection over many years in the course of our research into the specific geohazards that seismic activity creates.