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Seismic response

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Imagine a row of simple oscillators, with increasing natural frequency.
This is your x-axis.
An earthquake comes and it shakes that row for a while.
The motion of each oscillator is recorded. A peak response for each of those oscillators
is noted and marked on the graph, above the oscillator, giving you the y-value.
The entire graph is a response spectrum.
It can be for displacements, velocities or accelerations. (All oscillators have the same damping.)
Then comes your structure.
Each DOF is interpreted as an oscillator.
That mode will have the same peak accel as the corresponding oscillator had.
To get a response at a node, you combine all considered modal responses
according to some rules, for example SRSS. Same for bending moments, etc.
If you want a simple, basic presentation of the entire process,
you may look up my book "Dynamics of structures and machinery. Problems and solutions."
(Wiley 1982). It is out of print now, but you can still run into it. 
It doesn't tell you what codes of practice require, but gives good physical understanding.
Gregory from Oz.
Question from Alex Bausk:
If there is a task to calculate the response spectrum at a given node of th=
e structure (over frequency domain) from a given ground motion record (acce=
lerogram)=2C do I get it right that the only way to do this is to perform a=
 full-blown time-history analysis?
The logic behind this is=2C to calculate the spectrum you have to have the =
actual response record at the desired node=2C and the spectral approach won=
't produce this kind of information. Is this right?

Any reference to a textbook would be a very nice thing to have. Many thanks=
 in advance and sorry that I have flooded the list with my threads.