Basement- and roof-level velocity records were obtained in a 22-story reinforced concrete building in Reno, Nevada, for the nuclear event FAULTLESS. Analysis of these records indicates that the fundamental period of the building in the E-W direction for small excitations is 1.79 sec. Response calculations were made from an accelerogram, which was produced from the digitized basement-velocity record by filtering out the high-frequency noise and numerically differentiating the filtered result. Also, the equations of motion were recast in terms of absolute motion so that the response of the structure could be obtained by using a linear combination of the groundvelocity and displacement records as the forcing function. The ground displacement used in this treatment was obtained by integration of the velocity trace, corrected for baseline errors. These two methods gave virtually identical results and agree well with the measured roof motion.