...
Horizontal elastic design spectral accelerations Sa, are defined in terms of gravity [g] depending on the natural vibration period.
With the spectral response acceleration parameters obtained from USGS depending on the coordinates, the horizontal elastic design spectrum Sa isdetermined according to the formula below. It is represented by a total of 4 functions, different in each region. It’s It is shown in the graph below.
...
In the Analysis Settings - Response Spectrum Function tab, the horizontal design spectrum is determined and showed by shown using the design spectral response acceleration parameters.
...