A 39-story building in Seoul, South Korea was evacuated today when it reportedly began shaking and shuddering at 10:10 AM. The tremor was said to last for a total of 10 minutes. Roughly 3,000 people were in the building when the shaking started at the ‘Techno Mart‘, a skyscraper mostly containing 1,200 electronic discount retailers, a shopping center, and a multiplex movie theatre on the 10th floor.
There were no recorded earthquakes in the area and other neighboring buildings were apparently not affected. The shaking remains a mystery. There are several theories floating around including potential structural issues of vertical support beams, a gas explosion, or even the 12th floor sports center who had been playing loud music. Some also blame the movie theatre for the building shaking.
Having actually been inside this particular building and cinema during a previous career business trip, and having a professional knowledge in audio, the incident has captured my interest. Although not impossible, it is very highly unlikely that the cinema loudspeakers and subwoofers could have actually caused the entire 39-story skyscraper building to shake to the degree of panic and evacuation.
Having said that however, there IS an acoustic phenomenon, or vibration, that certainly could begin to shake a structure or mass, and at the extreme – could even shake a structure apart. That phenomenon is called ‘resonance’. In addition, it wouldn’t necessarily take a tremendous amount of energy to shake something to the point of resonance. Although high power or brute force will definitely assist the process, to achieve resonance could also be as simple as applying the proper frequency with just enough energy in such a fashion to add upon itself, or magnify itself in tandem with the properties or the mass, until the mass of the object itself has achieved a resonance.
The movie theatre at the Techno Mart would have been producing varying frequencies, more-or-less, and any rhythmic or resonant-inducing patterns would certainly be short lived within any given movie soundtrack so as not to induce a building debilitating resonance (haven’t heard of any movie multiplexes recently crumbling to the ground due to a new movie release with a VLF structure-crumbling subwoofer track…).
The situation does remind me of an episode of ‘Mythbusters’ that I saw some time ago where they actually were able to get a very large old suspension bridge to vibrate and resonate (to the point of being concerned, and shut it down) with a simple electronic linear motor which was tunable to .01 hertz increments (while attempting to mimic Tesla’s ‘earthquake machine’). The bridge was the original Carquinez bridge in the San Francisco bay area that was about to be torn down (and since has been).
The Mythbuster design was fashioned after the ‘Tesla Oscillator’ (or ‘earthquake machine’), a mechanical oscillator generator featuring a central rod, motor, and air cushion. The principle is that the speed of the vibration of the rod could be manipulated and with proper tuning, it could destroy anything.
Nikola Tesla actually patented the oscillator (US Patent# 514169) and claimed that such a device could destroy the Empire State Building with just 5 pounds of air pressure.
The destructive powers of mechanical resonance are well-known, with perhaps one of the most famous events being the Tacoma Narrows Bridge collapse in Washington state during 1940.
A poorly designed building could be susceptible to damaging resonance, which could even be induced by winds. The TechnoMart building however has been up since 1998 with no apparent previous incident. However it’s not beyond the realm of possibilities that something may have given way regarding the support of the building itself. If this is actually the case, the building is likely in imminent danger of collapse.
On the other hand, I’ve witnessed (on a small scale) the destruction that can occur due to out-of-control resonance, and sometimes wonder what kind of secret weapons have been designed around such theories (or are being designed)…
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