Gym workout caused Seoul building tremor

South Korean experts said Tuesday they believe a vigorous gym exercise session caused a high-rise building in the capital to shake for 10 minutes this month, prompting hundreds to flee in panic. They said tests showed that oscillations created by a group of Tae Bo practitioners on the 12th floor of the 39-story TechnoMart mall building apparently resonated through the structure. Tae Bo is an aerobic exercise routine that involves performing the motions of boxing and martial arts such as Taekwondo at a rapid pace. Professor Chung Lan of Danguk University in Yongin City near Seoul linked the incident to a physics principle under which catastrophic failures can occur when the vibration of a structure is matched by another source. He told a radio programme that the building, constructed from iron girders and cement, had a characteristic vibration frequency which was "in phase" with the synchronised movements of the Tae Bo practitioners, Chung and six others re-created the scenario which caused the panic on July 5 with a group of 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. On the first occasion hundreds fled the building as it 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. Cho Byung-Joon, chief of the district government's flood control and disaster prevention division, said the professor and other experts would carry out a test before news media and officials later Tuesday to prove their theory. "When they show the test results to us and with data, we will immediately let people use the fitness club," he told AFP. "But practising Tae Bo in that particular building may have to be banned."