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. 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 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:
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.
Colorado Geological Survey