Magnitude 5.3 Quake Rattles Colorado

[Pathfinder]

Magnitude 5.3 Quake Rattles Colorado

Trinidad Still Feeling Aftershocks
April Schildmeyer, News Producer

POSTED: 4:08 am MDT August 23, 2011
UPDATED: 6:45 am MDT August 23, 2011


TRINIDAD, Colo. -- The largest earthquake to strike Colorado in almost 40 years has shaken hundreds of people near the New Mexico border.

The magnitude 5.3 earthquake was recorded at about 11:46 p.m. MDT Monday about nine miles southwest of Trinidad, Colo., and about 180 miles south of Denver, according to the National Earthquake Information Center in Golden.

By 4 a.m. more than 900 people had logged on to the USGS website to report feeling the quake...

More:
http://www.thedenverchannel.com/news/28946825/detail.html

 

[Emily]

Re: Magnitude 5.3 Quake Rattles Colorado

http://coloradoindependent.com/97225/past-earthquakes-in-southern-colorado-studied-for-links-to-gas-fracking-water-disposal
Past earthquakes in southern Colorado studied for links to gas fracking, water disposal
By David O. Williams | 08.24.11 | 9:09 am

http://pubs.usgs.gov/of/2002/ofr-02-0073/ofr-02-0073.html#_Toc2571756

Open-File Report 02-0073

2002

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

U.S. Department of the Interior
U.S. Geological Survey

Abstract

A swarm of 12 widely felt earthquakes occurred between August 28 and September 21, 2001, in the area west of the town of Trinidad, Colorado. The earthquakes ranged in magnitude between 2.8 and 4.6, and the largest event occurred on September 5, eight days after the initial M 3.4 event. The nearest permanent seismograph station to the swarm is about 290 km away, resulting in large uncertainties in the location and depth of these events. To better locate and characterize the earthquakes in this swarm, we deployed a total of 12 portable seismographs in the area of the swarm starting on September 6. Here we report on data from this portable network that was recorded between September 7 and October 15. During this time period, we have high-quality data from 39 earthquakes. The hypocenters of these earthquakes cluster to define a 6 km long northeast-trending fault plane that dips steeply (70-80?) to the southeast. The upper bound of well-constrained hypocenters is near 3 km depth and lower bound is near 6 km depth. Preliminary fault mechanisms suggest normal faulting with movement down to the southeast.

Significant historical earthquakes have occurred in the Trinidad region in 1966 and 1973. Reexamination of felt reports from these earthquakes suggest that the 1973 events may have occurred in the same area, and possibly on the same fault, as the 2001 swarm.

In recent years, a large volume of excess water that is produced in conjunction with coal-bed methane gas production has been returned to the subsurface in fluid disposal wells in the area of the earthquake swarm. Because of the proximity of these disposal wells to the earthquakes, local residents and officials are concerned that the fluid disposal might have triggered the earthquakes. We have evaluated the characteristics of the seismicity using criteria proposed by Davis and Frohlich (1993) as diagnostic of seismicity induced by fluid injection. We conclude that the characteristics of the seismicity and the fluid disposal process do not constitute strong evidence that the seismicity is induced by the fluid disposal, though they do not rule out this possibility.