Swaying floor lamps and dizziness: In Berlin on Friday evening, several residents in the south of the city reported vibrations on social networks.

However, it was not an earthquake, as Jens Skapski from the privately operated portal "Erdbebennews" announced on Saturday.

"Although an earthquake can be ruled out with certainty, some nearby stations recorded a low-frequency signal lasting about a minute," Skapski wrote on his website on Saturday.

This also fits with the reports of "noiseless, weak swaying, which was mainly noticed on the upper floors".

Evaluations from three private seismological stations would have resulted in a magnitude of 1.4 and a tremor area around the Tempelhof field - "that is equivalent to a small earthquake",

But what triggered the tremors?

That cannot be said with certainty, Skapski continued.

The signal speaks for an "industrial or human source".

And that can probably be seen on Tempelhofer Feld: the “Tempelhof Sounds” festival took place there on Friday, for which around 35,000 visitors were expected in advance.

At the time of the measurements used by Skapski - between 8:58 p.m. and 8:59 p.m. - the band "Florence + The Machine" was performing there.

As a Twitter user commented under a post on the portal, there was a moment around 9 p.m. “where quite a few jumped at the same time”.

The vibrations were also felt at the concert venue.

When asked by a Facebook user, Skapski explained with the underground that such tremors do not occur regularly, even at significantly larger events.

"Above all, it needs a (water-saturated) floor that absorbs the energy of the jumping crowd and transmits it well," he wrote.

Ole Roß from the Federal Institute for Geosciences and Natural Resources (BGR), whose tasks also include the federal earthquake service, doubts that the tremors were an earthquake in the classic sense.

However, he considers a concert to be a plausible trigger: Jumping and cheering could certainly cause measurable shocks.

According to Roß, an acoustic transmission is also a conceivable trigger, for example through the deep sound of a bass system.

However, the maximum energy that more than ten thousand visitors can release through resonant, rhythmic hopping is close to the vibrations recorded by the private exhibition sites.

The BGR also received a report from a citizen from Berlin regarding Friday evening, but their own measurement data still had to be evaluated.