Colorado’s Largest Earthquakes

Colorado’s historic record of earthquakes dates back to 1870.

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.

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 Colorado’s 1882 earthquake was derived in this manner.

Ground acceleration is measured as a percentage of the force of gravity by strong motion instruments. These are used in the National Earthquake Hazard Maps for 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 following table provides information and links to a historical database about Colorado’s largest earthquakes:

Date Location Magnitude Maximum Intensity
1870, Dec 4 Pueblo / Ft. Reynolds ** VI
1871, Oct Lily Park, Moffat County ** VI
1880. Sep 17 Aspen ** VI
1882, Nov 7 North Central Colorado 6.6* VII
1891, Dec 1 Axial Basin (Maybell) ** VI
1901, Nov 15 Buena Vista ** VI
1913, Nov11 Ridgway Area ** VI
1944, Sep 9 Montrose/Basalt ** VI
1955, Aug 3 Lake City ** VI
1960, Oct 11 Montrose/Ridgway 5.5 V
1966, Jan 5 NE of Denver 5.0 V
1966, Jan 23 CO-NM border near Dulce, NM 5.5 VII
1967, Aug 9 NE of Denver 5.3 VII
1967, Nov 27 NE of Denver 5.2 VI
2011, Aug 22 Trinidad (Cokedale) 5.3 VII
* Magnitude for this older earthquake is estimated from historic felt reports
(Spence and others, 1996). Other magnitudes are body-wave magnitudes
reported by Stover and others (1988) and Kirkham and Rogers (2000)
**Historic event pre-dates available seismometer data.

The table below details the scale used to measure the felt intensity of an earthquake event:

Magnitude Typical Maximum Intensity*
1.0 – 3.0 I
3.0 – 3.9 II – III
4.0 – 4.9 IV – V
5.0 – 5.9 VI – VII
6.0 – 6.9 VII – IX
7.0 and higher VIII or higher
*Maximum Intensity Scale Defined:
  • I – Not felt except by a very few under especially favorable conditions.
  • II – Felt only by a few persons at rest, especially on upper floors of buildings.
  • III – Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
  • IV – Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
  • V – Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
  • VI – Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
  • VII – Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
  • VIII – Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
  • IX – Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
  • X – Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
  • XI – Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
  • XII – Damage total. Lines of sight and level are distorted. Objects thrown into the air.

Denver – August 9, 1967 – Magnitude 5.3 earthquake

The most economically damaging earthquake in Colorado’s history occurred on August 9, 1967 in the northeast Denver metropolitan area. This magnitude 5.3 earthquake, centered near Commerce City, caused more than a million dollars ($7 million in 2012 dollars) in damage in Denver and the northern suburbs. This earthquake is believed to have been triggered by the deep injection of liquid waste into a borehole at Rocky Mountain Arsenal. It was followed by an earthquake of magnitude 5.2 on November 27, 1967. For more detailed information on the August 9, 1967 event, click here.