-9Near the source the pattern of seismic radiation can be measured by appropriate instrumentation. At greater distances, the seismic waves result in vibrations or motion of the ground, the objective of concern by safety. To determine the probable effect of these ground motions upon buildings and other structures, the characteristics of the structure are determined by engineers skilled in the interpretation of spectral response. Each building vibrates in response to ground motion at characteristic frequencies. For some of these frequencies, the motions of the building are larger than others. The task of the structural engineer is to relate the natural frequencies of a structure to the spectral content of ground motion and thereby determine the probability whether the structure will vibrate to a dangerous degree or not. You will hear more about these details in the papers which follow. DOE ARCHIVES