That Rumble You Heard Thursday at Lunchtime Was an Earthquake in Cos Cob

Around lunchtime on Thursday a loud rumble startled Greenwich residents.

Shortly after, people turned to Facebook to share experiences and guess the source of the loud boom. In downtown this reporter heard a loud rumble for about 3 or 4 seconds, similar to the boom of a blown transformer, but longer. The noise came distinctly from the east of downtown.

Greenwich Police didn’t share any information related to damage or public safety.

Residents turned to the Greenwich Connections page on Facebook, a popular forum for local conversations, where someone guessed it had been a sonic boom, the sound associated with shock waves created when an object travels through the air faster than the speed of sound…

… or a water main break, or a meteor, or aliens landing.

Turns out it was an earthquake centered in Cos Cob with a 1.4 ml (Richter local magnitude) and a depth of 3.1 miles. It occurred at 12:38:24pm, according to the United States Geological Survey‘s Earthquake Hazards Program, which is responsible for monitoring, reporting, and researching earthquakes and earthquake hazards.

To look it up yourself go to US Geological Survey, Earthquake and select 1 day all magnitudes along the right hand column and switch the default from kilometers to miles.

Back in 1979, Greenwich experienced an earthquake with a magnitude of 2 or 2.1 on the Richter scale, slightly bigger than Thursday’s. At the time that as considered “very tiny,” which makes Thursday’s earthquake with a magnitude of 1.4, very very tiny.

Their website has an interactive search. The maps and lists show events which have been located by the USGS and contributing agencies within the last 30 days. They should not be considered to be complete lists of all events in the U.S. and adjacent areas and especially should not be considered to be complete lists of all events M4.5+ in the world.

There is even a feature “Felt Report – Tell Us.”

Another website where you’ll find information on the earthquake in Cos Cob is at