Calls to the local police flooded in as sleepy Germans saw their cups of coffee fall off tables and bedroom walls shake at 7am in Haltern am See, North Rhine-Westphalia.
“The entire house sunk down and then swung violently from side to side,” wrote local geology student Jens Skapsi on his website, shortly after the quake. “It was the first time in 30 years that I was scared the house would collapse.”
Mining used to be widespread in the area, and experts believe that shifting earth in old mine shafts caused the ground to shake, regional newspaper the Westdeutsche Allgemeine Zeitung reported.
Occasional tremors caused by sagging mining tunnels have hit the region in the past – but measuring between three and 3.6 on the Richter scale, geologists say Friday morning's was the strongest in years.
A seismologist from Bochum university – which measures the area's tremors from 13 different stations – Sebastian Wehling-Benatelli said that although the quake registered high, this did not necessarily equate to it causing lots of damage. There had been smaller ones that had more impact.