I recently read that a copyright does not apply to real, live performances (you couldn't
record yourselves live and sell that recording, without paying royalties).
I know we have talked about this topic before. Let me see if I can find it for you.
EDIT: Here it is:
Band name copyright?.
Also, I don't recommend calling yourself a Weezer tribute band unless you are one. When someone goes to hear a tribute band, they expect to hear a band that sounds exactly like the original band and has at least one or two guys that look like the original band. Maybe when you advertise your band's name, you should just mention that you feature some of Weezer's music (unless you are an honest-to-goodness tribute band).
Good luck.