The design acceleration spectrum in ASCE 7 relies on SDS and SD1. If you have that figure, how would you construct the displacement response? 

I'm attempting to use the displacement-based design method, but I'll need this diagram to calculate the equivalent period (Teq). The maximum displacement allowed is already known to me. 

My first thinking was to integrate twice; however, since this is a response spectrum rather than an actual recording, this results in colossal displacement values.