-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.
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