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August 23, 2011
Heidi  Koontz 303-202-4763 hkoontz@usgs.gov
Marisa Lubeck 720-891-3215 mlubeck@usgs.gov
National Earthquake Information Center  303-273-8500

Magnitude 5.3 Earthquake Rattles Southern Colorado

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A magnitude-5.3 earthquake rattled southern Colorado Monday, August 22, at 11:46PM MDT, causing strong shaking, but minor damage, and was felt throughout the state of Colorado and neighboring states. The USGS Prompt Assessment of Global Earthquakes for Response (PAGER) system issued a Green Alert, indicating a low probability for fatalities or significant economic losses.

The earthquake occurred approximately nine miles southwest of Trinidad, Colo.

This was the largest earthquake in Colorado since a M5.3 in August, 1967 at Rocky Mountain Arsenal. The largest earthquake in Colorado history was Nov 7th, 1882, near Rocky Mountain National Park; estimates vary but it was about a Magnitude 6.5. 

Yesterday's M5.3 had three detected foreshocks (M4.6, 3.0 and 2.9), and there have been many recorded aftershocks.

Citizens who felt the earthquake can go online and report their observations on the USGS Did You Feel It? website. Over 1,000 reports of felt shaking have already been received from more than 200 zip codes in six states.

Earthquakes cannot be predicted. This area in Colorado has a history of earthquakes, notably a swarm that occurred in 2001, with earthquake magnitudes between M2.9 and 4.6.  A USGS report on those earthquakes is available at the USGS Earthquake Hazards Program website

For more information on earthquake and other hazards, please visit the USGS Natural Hazards website. The USGS operates a 24/7 National Earthquake Information Center in Golden, Colo., that can be reached for more information at (303) 273-8500.


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