Torsional mode; Period = 1.06 sec
"Seismic ground motions are predominantly translational, not rotational. However, where the centres of mass and stiffness of a structure do not coincide, coupled lateral torsional response occurs, as shown above. Structures with signicant torsional eccentricity are found to have a much worse performance during an earthquake."
Edmund Booth, from 'Analysis for earthquake effects' in 'Concrete structures in earthquake regions'