I'm no structural engineer, but I think I understand the concept.

A building, when subjected to lateral motions, acts like a pendulum. It flexes and sways with a frequency dependent upon the elasticity of its components. If this frequency is resonant with seismic frequencies you get sympathetic vibration. Even the motions of a small earthquake can make a building flex beyond its structural integrity resulting in failure.

By adding in the walls between the columns you change the resonant frequency of that part of the building, thus not allowing the sympathetic vibrations caused by seismic waves.

Brian