Gym workout caused tremor at Seoul building

South Korean experts believe a vigorous exercise class caused a high-rise building in the capital to shake for 10 minutes this month, prompting hundreds to flee. They said tests showed that oscillations created by a group of tae bo practitioners on the 12th floor of the 39-storey TechnoMart mall building apparently resonated through the structure.

Tae bo is an aerobic exercise that involves performing rapidly the motions of boxing and martial arts such as taekwondo. Chung Lan, of Danguk University in Yongin City, near Seoul, linked the incident to a physics principle under which catastrophic failures can occur when another source matches the vibration of a structure. He said the building, made of iron girders and cement, had a characteristic vibration frequency that was ''in phase'' with the synchronised movements of the tae bo practitioners.



Professor Chung and six others recreated the scenario that caused the panic on July 5 - with 17 middle-aged people working out to the tune of a pop song, The Power by German group Snap - and said the building shook in a similar way. In the original incident, hundreds fled as the building shook for about 10 minutes. The Gwangjin district government ordered the mall closed but reopened it after experts said it was structurally sound. The gym remains off-limits.

''Practising tae bo in that particular building may have to be banned.'' said Cho Byung-joon, chief of the district government's flood control and disaster prevention division. He said Professor Chung and other experts would carry out a test before news media and officials.