User blog comment:KrusH HsurK/Earth, Capital of humanity, but lacking of its own capital?/@comment-1388547-20120508211538/@comment-99.1.241.31-20120508215939

It's mentioned I think at the beginning of ME3 that London also functions as a SA base. Also, Anderson mentions that several cities have QE Communicators - which is super high end alliance tech. Makes sense that it would be found on certain bases.

BTW: Kaidan mentiones that he grew up in Vancouver and that his parents were military so it lends to the idea that Vancouver is the main Earth facility for SA. Seeing as the Committee being there, it feels like Vancouver operates as the Earth HQ for SA.