An earthquake of magnitude 3.7 struck Las Animas County at 1:55 a.m. Sunday, November 1, about 11 miles south-southwest of Weston and 10 miles south of Stonewall Gap, a few miles north of the New Mexico line, according to the U.S. Geological Survey. The quake was about 6 miles deep. No damage or injuries were reported.

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Three people had told the agency's "Did You Feel It?" survey by Sunday morning that they felt it, all in Trinidad, 27 miles to the east, where they rated the shaking weak. The agency's shake map estimates light shaking, intensity 4 on the 12-point scale, close to the epicenter, in the sparsely settled country of the upper Purgatoire River between Weston and the Sangre de Cristo foothills. Raton, New Mexico, is 29 miles away and Walsenburg 44.

The Geological Survey located the quake with readings from 20 seismic stations and puts the horizontal uncertainty at about a mile and a half. It is the strongest earthquake on the Colorado side of the basin since a magnitude 3.8 southeast of Stonewall Gap on June 20. Larger ones have struck just across the line this year: a magnitude 4.1 on May 7 about a mile south of the state line, and a magnitude 3.8 south of Segundo on July 6, both in Colfax County, New Mexico.

A basin that keeps shaking

Sunday's quake was the 22nd earthquake of magnitude 2.5 or greater in Colorado this year, and the eleventh on the Colorado side of the Raton Basin, the coal country along the Colorado-New Mexico line south and west of Trinidad. Within 30 miles of Sunday's epicenter, on both sides of the state line, the Geological Survey's catalog lists 25 earthquakes of that size in 2026 and more than 400 since 2000. The rest of the state's quakes this year were scattered: three near Walsenburg, and single events near Colorado City, De Beque, Dotsero, Silverton, Sawpit, Redstone, Meeker and in Garfield County.

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The basin's earthquakes are not a mystery. A Geological Survey study published in 2014 concluded that deep injection of wastewater from coalbed methane wells was responsible for most of the earthquakes in the basin since 2001, when the shaking picked up sharply, about a decade before the rise in induced earthquakes across the central United States. The largest, a magnitude 5.3 near Trinidad on August 23, 2011, was the largest earthquake in Colorado since 1960, tied with a 1967 quake northeast of Denver, according to the Colorado Geological Survey. A magnitude 5.0 struck 12 miles south of Weston in August 2005.

In a 2023 presentation summarized by the Geological Survey, agency seismologist Margaret Glasgow described three zones of earthquakes in the basin, each made up of short faults a mile or two long rather than the single long faults researchers once assumed. Earthquakes in the Trinidad zone, where the 2011 quake struck, have dropped off since about 2016, she said, most likely because wastewater injection nearby was cut by about 80 percent. Sunday's quake and most of this year's are in the hills along the state line south of Weston and Stonewall Gap, west of the Trinidad zone, which the Press has reported on in June and in July.

What to do

The Geological Survey asks anyone who felt the earthquake to report it on the event's page, where "Did You Feel It?" responses help map how far the shaking reached. For a larger quake, the advice from the Great ShakeOut drill is to drop, cover and hold on, stay away from windows, and if outdoors, move away from buildings and power lines. The Colorado Geological Survey rates the state's earthquake hazard as low to moderate and counts more than 700 earthquakes of magnitude 2.5 or greater since 1867.