EL MORO, Colo. (KXRM) — A magnitude 3.1 earthquake was reported in southern Colorado, 3 miles west of El Moro late Tuesday night, according to the United States Geological Survey.

The earthquake occurred in Las Animas County at approximately 11:36 p.m. at a depth of about 4 miles, per USGS.

Community Determined Intensity data collected from 23 responses gave the earthquake a Level III intensity rating out of 10. Level III earthquakes are “weak” and noticeably felt by those indoors, especially on upper floors of buildings, USGS says. These earthquakes may slightly rock standing cars and cause vibrations similar to the passing of a truck.

USGS says earthquakes in North America east of the Rocky Mountains are uncommon.

Earthquakes in this region are typically felt over a much broader region – usually 10 times larger – than earthquakes of similar magnitude on the west coast. As such, large and damaging earthquakes east of the Rockies centered in populated areas are likely to cause damage out to greater distances compared to earthquakes of the same magnitude centered in western North America.

According to USGS, earthquakes that occur east of the Rockies are a result of faulting within bedrock, usually miles deep. However, few earthquakes in this region have been surely linked to mapped geologic faults.

Scientists who study earthquakes in eastern and central North America often hypothesize that modern earthquakes occur due to a slip on preexisting faults formed in earlier geologic eras, which have been reactivated under the current stress conditions. USGS says the bedrock of Eastern North America is interlaced with faults that were active in earlier geologic eras, few of which are known to be active in the current geologic era.

In most areas east of the Rockies, the likelihood of future damaging earthquakes is estimated from the frequencies and sizes of current earthquakes as well as those documented in historical records.