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4.5 magnitude earthquake in western Colorado likely human caused

Data pix.

DOVE CREEK, Colo. -- A 4.5 magnitude earthquake Monday morning in western Colorado may have been triggered by a salinity control project.

The earthquake's epicenter is located in the Paradox Basin, a remote part of the state. However, it was felt by people more than 100 miles away.

Alex Koch is one of many Coloradoans who felt the quake. He lives about 20 miles from the epicenter.

"It was two separate jolts about 15 to 30 seconds apart. I was sitting at my desk doing tax work and the chair shook," said Koch.

The Bureau of Reclamation's 2.9-mile deep Paradox Valley Unit brine injection well is located along the Dolores River. The facility is designed to improve water quality in the river by removing salt from the groundwater before it enters the river. That's done by extracting salt brine and injecting it deeper underground.

The USGS monitors seismic activity in Colorado and has been observing a spike in man-made induced earthquakes, not just in the Paradox Valley, but statewide.

"Certainly, we've been recording more over the past five to 10 years," explained Gavin Hayes, a geophysicist with the USGS.

Most induced earthquakes in Colorado are triggered not by the injection of brine, but of wastewater into the ground after fracking. Most are so small they cannot be felt.

"Think of it like blowing up a balloon. When you pump things into the subsurface at high pressure, it's like blowing up a balloon and that causes pressure changes, stress changes on the faults and subsurface," said Hayes.

While Monday's quake had nothing to do with oil development, scientists believe it was likely triggered in the same way.

"There have been six aftershocks so far, all very small. I think the largest is a magnitude 2.1," said Hayes.

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