Magnitude 4.0 quake rattles near Weston, may have been felt widely

A magnitude 4.0 earthquake shook the ground 17 kilometers south-southwest of Weston on May 7, a size and location that put Las Animas County back on notice about a hazard most residents rarely think about. The U.S. Geological Survey recorded the event at 17:44:24 UTC, with a preferred origin at 36.985°N, 104.930°W and a depth of 8.7 kilometers.

The agency later updated its main event page to show a headline magnitude of 4.1 and a location 18 kilometers south-southwest of Weston at a 2.0-kilometer depth, while the origin detail still listed the 4.0 magnitude and deeper hypocenter. The quake was cataloged as us6000svzn and reviewed by a scientist, underscoring that the reading was not just a casual report but part of the official seismic record for southern Colorado.

For people in Trinidad, Weston and surrounding ranch country, the more important question is how widely a quake like this can be felt. USGS says earthquakes east of the Rockies can be felt across an area more than ten times larger than similar quakes on the West Coast, and that a magnitude 4.0 event in eastern or central North America may be felt by many people more than 100 kilometers away. That helps explain why the shaking could be noticed well beyond Las Animas County, including reports that it may have been felt near Pueblo.

A third-party tally based on USGS data said 40 people reported feeling the quake, with a maximum reported intensity of MMI 5.0. The USGS event page also included a Felt Report section, showing that residents were actively logging what they experienced after the shaking passed.

A public-information notice from the Colfax County Fire Marshal’s Office described the earthquake as light, saying it could shift items and cause cosmetic cracking but typically little to no serious structural damage. That is the kind of description local officials watch closely in a region where schools, public buildings and first responders would be expected to deal first with inspections, reports of cracks and possible utility issues before any bigger response.

The timing matters, too. USGS recorded another quake in the same area on April 10, when a magnitude 3.4 event struck 17 kilometers south-southwest of Weston at a depth of 6.8 kilometers. The repeated activity fits the broader pattern in the Raton Basin of Colorado and New Mexico, where USGS has identified induced-earthquake hazard concern and noted that some central and eastern North America quakes are tied to preexisting faults, and in some cases induced seismicity.