You need to set up a modal analysis before you can set up a seismic analysis. 
- Click Analysis 
 Analysis Types.  The Analysis Types dialog opens.  
- Click New.  The New Case Definition dialog opens. 
 
- Select Seismic, and then select the code according to which you want to run the calculations. 
 
- Click OK.  The Parameters dialog opens for the selected code. 
 
- Specify the required code parameters, and then click OK.