Middle-aged fitness fanatics don't mix with skyscrapers, according to the "tentative" conclusions of an investigation into the strange shaking that brought about the evacuation of the 39-story Techno Mart in northeastern Seoul on July 5.

After the original panic, the building’s owner, Prime Development, had speculated that “loud music” from the 12th-floor exercise club, or perhaps from the building’s multi-screen cinema complex, caused the shaking.

The Architectural Institute of Korea has now lined up with the “health club” hypothesis. The The Korea Times reports that the investigation is blaming boomer practitioners of “tae bo” at the exercise club for the building’s bad vibe.

The inspection committee decided to test the idea, and in Mythbusters style, reproduced the exercise in a ‘simulation’ last Sunday (El Reg: how do you ‘simulate’ an exercise which itself is a simulation of tae kwon do combined with boxing?).

According to the Korea Times, the group of professors and vibration experts “used a Doppler vibrometer while performing the same kind of aerobic exercise”, and measured shaking at the 38th floor that was “ten times normal”. Lower floors, however, were unaffected, indicating that six academics just aren’t enough to rattle a skyscraper.

Professor Chung Lan of Dankook University said a new fitness instructor drove the class twice as hard as usual in the exercise, and “that must have been the reason”.

Ever since the Tacoma Narrows Bridge shook apart (see YouTube) in 1940, engineers and architects have known that it’s better to work with resonance rather than against it, but the 3,000 people involved in the original evacuation remain unimpressed with the official version. ®

Bootnote: Which do you suppose will come first? The Mythbusters test, or the new Internet fad of "skyscraper shaking"?