How can we improve our structural design in frequency domain? What are the frequencies of the earthquake we have to consider during seismic design?

the dynamic response of structural systems, facilities and soil is very sensitive to the frequency content of the ground motion. The frequency content describes how the amplitude of a ground motion is distributed among different frequencies. Using Fourier transformation we can find the Frequencies content from shifting from the period domain to the frequency domain. Regarding the Period we should differentiate between the site period (soil period) and the natural period of the building.

When resonance happen, the Two periods are close or equal ,there is a great amplification of the earthquake effect and thus greater damage will occur. There are many techniques to calculate the natural period of a building. So to conclude depending on the location of the building you can compare the Site Period to the natural period of the building to make sure they don't resonate.