From what I know, which really is kind of hazy. The people I learned it from have gotten it second or fifty-seventh handed knowledge.

The rifts are caused by ...mm... backlash from when the original portal was closed. It's a sort of cross between technology and magic. Anti-matter and matter getting all happy together? Sort of?

Currently they're opening up at random, to random locations. There's nothing that we can tell that causes them to open.

As for the same thing as what pulls you to the City... mm... no... I don't think so.