Hi Ed,
The displacement values given by a modal analysis are NOT to be interpreted as real displacement values.
This is logical as forces are not defined in Modal analysis, so there is no reference to calculate the intensity of load hence displacement.
The disp. values are to be interpreted as an indicator of relative displacement within your design (which point will displace the most as compared to the other points in the model).
The only output that have physical meaning from a modal analysis is the Frequency and the mode shape (again relative displ. and not absolute).
To calculate the real value of displacment, one will need to apply the forces with their real value+direction+variation along time ; hence a linear dynamic or MES should be carried out.
Hope this explains.
Regards,
Shakeel
