professor hisada is an expert in seismic engineering. he ran simulations to reproduce the vibrations of the building based on the seismic data on march 11th. >> translator: the quake severely volted upper floors but also bending on the mid-level. >> reporter: the building made large swaying motions much like a dancer's hips rotating. >> translator: the movement is called the secondary mode. >> reporter: the secondary mode is repeated in short cycles. the vibrations are different in nature from the long period motions. the long period motions that sway the top floors of high-rises are called primary mode movements. the secondary mode, on the other hand, has shorter cycles and effects the mid-level floors most seriously. in the march 11th quake, a massive slippage took place along the faultline. this triggered two shock modes simultaneously. the primary mode jolted the upper mode and the secondary mode caused significant damage to the mid-level floors. so now we know major quakes generate a secondary shock mode that can effect buildings. t

professor hisada is an expert in seismic engineering. he ran simulations to reproduce the vibrations of the building based on the seismic data on march 11th. >> translator: the quake severely volted upper floors but also bending on the mid-level. >> reporter: the building made large swaying motions much like a dancer's hips rotating. >> translator: the movement is called the secondary mode. >> reporter: the secondary mode is repeated in short cycles. the vibrations are different in nature from the long period motions. the long period motions that sway the top floors of high-rises are called primary mode movements. the secondary mode, on the other hand, has shorter cycles and effects the mid-level floors most seriously. in the march 11th quake, a massive slippage took place along the faultline. this triggered two shock modes simultaneously. the primary mode jolted the upper mode and the secondary mode caused significant damage to the mid-level floors. so now we know major quakes generate a secondary shock mode that can effect buildings. t