In fact, the racket was caused by RAF jets when they broke the speed of sound.
An Essex police spokesman said there were several reports of sonic booms in the county "caused by military aircraft engaged in routine operations."
Twitter users took to the social media site after the noise:
I think essex/Hertfordshire just had an earthquake/explosion! Everyone is out on the street! #BANG
So the Essex/Hertfordshire "explosion" was actually a sonic boom! Absolutely bizarre. People thought it was an earthquake.
Just felt and heard a large explosion in Essex #chelmsford
The Ministry of Defence said it was caused when the jets were responding to another aircraft which lost communication.
A spokesman said the jets soon established "everything was fine" with the aircraft.