For simpler buildings we can use response spectrum analysis. How is this used? The maximum acceleration we get from this , is simply multiplied by the mass of the building to get F=ma , total earthquake force on the building? Simple as that?
Yes, Right. After you verify that your building structure geometry and utility make it qualify for using design spectra charts:
it gives you the acceleration Sa and speed of ground motion, Sv and the amount of motion, Sd which are all related by factors of $ \omega$.
Then you can apply F=ma. Ther are inherent errors in this method that a designer must be aware of and use good judgment. Search for - (Nigam and Jennings, 1969), to see the article on the errors.
here is the chart.