Jumping in a fitness center is believed to have caused the shaking of the 39-story shopping mall in Seoul that had forced the evacuation of hundreds of tenants earlier this month, experts said Tuesday.

The upper floor of TechnoMart, which houses hundreds of electronics retailers and commercial offices, rocked up and down for about 10 minutes on July 6 for no apparent reason. Authorities evacuated the building for the next three days for an emergency safety check and a team of architects and seismologists have tested the building over the weekend to figure out the cause of the vibrations.

“As a result of experiment results, we have tentatively concluded that jumping in the fitness center caused the tremor in the building,” said Chung Lan, an architecture professor at Seoul’s Dankook University who participated in the safety check.

“If the vibration is caused by structural problems, a strong shaking would briefly come and then go. Because this lasted for 10 minutes, we conducted a test as it seems to have originated from internal problems,” he said.

During an experiment in which people ran and jumped in the fitness center on the 12th floor, the inspection team detected a similar kind of vibration in the upper part of the building, Chung said.

Regarding the safety of the building, now back to normal operation, the professor said there is “very little possibility” that the steel-framed building would collapse any time soon as it is flexible, unless such a tremor lasted for hours.

Built in 1998, the 189-meter-tall high-rise passed a less rigorous checkup in March, according to authorities. 

(Yonhap News)