On August 8, 1982, the good people of London began ringing up their local police. "Feel that, mate? That's a bleedin' EARTHQUAKE! In London!"
So many calls came in that various constabularies telephone the British Geological Survey. "We're getting calls saying that parts of the city are swaying. Is Her Majesty's island about to sink?"
Seismologists were stumped. They checked their instruments and they found that, no, there wasn't an earthquake--but there had been some kind of seismic disturbance. What was responsible for all the shaking and rumbling?
In a word, ska.
At the moment the shaking started, Madness was playing a gig at Finsbury Park in North London. This is a statement from the UK Health Protection Agency (via Wikipedia):
One of the most bizarre investigations conducted by BGS using its seismic network, was in connection with an earthquake reported to be felt strongly in North London in August 1992 when three blocks of flats (8-9-storeys) were evacuated following minor damage that included cracked windows and a cracked balcony. Our seismic network showed that there had not been an earthquake or an explosion, and we were able to deduce that the cause was resonance set up by dancers at a Madness rock concert in nearby Finsbury Park. The resonance frequency of such dancing, in harmony, is tuned to the natural frequency of apartment blocks of this height, so that the movement is amplified.
Cool, huh? For years, this was the only example of seismic activity that could be attributed to live music. But now the Foo Fighters seem to have reached this same realm.
According to GeoNet and the BBC, Tuesday's Foos concert in Auckland had this effect:
The concert vibrations were recorded as a semi continuous harmonic signal with a peak osculation of 3Hz, ie the ground was shaking 3 times per second in a nice rhythmic motion. There are lulls in the signal between the songs and peaks in signal intensity during the songs.
The cause of the shaking is most likely the weight of the 50,000 fans dancing, as 50,000 fans is equal to around 5,000 tonnes of mass moving(or moshing)on the ground for the duration of the concert. This set up a nice harmonic vibration in the ground which was recorded in our nearby borehole seismometers.
The UK has little to worry about when it comes to earthquakes. New Zealand's techtonic issues are well known. This must have scared the crap out of people.
(Thanks to Greggory for finding the story.)