Another quake strikes near New Castle

The third and largest earthquake in the Silt-New Castle area in about three months struck Monday afternoon, prompting Colorado’s oil and gas agency to again look at any possible relation to local wastewater injection wells.

The 3.3-magnitude quake occurred about 1:46 p.m. three miles south of New Castle, the U.S. Geological Survey reported. The epicenter was an estimated three miles underground. By later Monday afternoon, a half-dozen people reported on a USGS website having felt the quake.

On Christmas night a magnitude 2.9 quake struck west of New Castle and just south of the Colorado River. On Oct. 23 a magnitude 2.1 quake struck just north of the Christmas quake, immediately across the Colorado River and Interstate 70.

This month, some 20 small earthquakes from magnitude 1.0 to 2.8 hit farther east, in the Marble/Redstone area. Most occurred within about a 13-hour period.

The New Castle earthquakes have drawn the attention of the Colorado Oil and Gas Conservation Commission because of the presence of injection wells in that area, generally south of New Castle and Silt. The agency’s policy calls for it to monitor areas where there are injection wells and temblors of magnitude 2.5 or higher occur. It found no direct correlation between the Christmas quake and injection wells.

The commission believes local injection wells aren’t operating at high enough pressures and injection-volume rates to have caused the Christmas quake. Stuart Ellsworth, the agency’s engineering manager, said Monday that history also has shown that earthquakes can result where injection is occurring in the area of “basement” granite rock.

But he said the point of injection for the wells in the area of the Christmas quake has some 9,000 feet of sedimentary rock between it and the basement rock.

He said an earthquake in the Greeley area linked to an injection well had a large number of smaller quakes preceding it — far more than one a month.

Still, he said he will be taking a close look at Monday’s quake to see if injection wells could have played a role.

“There’s definitely some work I need to do to get a few answers here,” he said.

Jessica Turner, a USGS seismologist, said her agency also would be reviewing past seismic activity in the New Castle area and watching closely for future activity, especially with the oil and gas development occurring in that area.

“When a magnitude 3.3 occurs we’re definitely going to pay extra-special attention,” she said.

But she said it would take a lot of earthquakes in an area to make a connection to an injection well, and Monday’s event may just have been another naturally caused earthquake, she noted.

“A 3.3 could happen pretty much anywhere in the world,” Turner said.


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