How to generate large dynamic backgrounds

I'm trying to work out how to produce dynamic backgrounds for my game. While searching around I've come across this image which looks exactly like what I'm aiming to do.

Ignoring the foreground stuff, I can't for the life of me figure out how one would go about generating the background rings and the general gradient blue glow. From poking about, I happen to know that this image:

• Is generated dynamically on the fly (any colour scheme, different ring patterns etc)

• Looks good at high zoom levels (see below)

I've tried writing directly to a texture using the sum of multiple functions (e.g. e^(-|x^2 + y^2 - r^2|) to index into a colour gradient, with each function representing one ring with radius r. However in order to be able zoom in even a little bit and keep the image sharp, the resulting texture needs to be huge (!) and takes forever to draw.

Anyone have any smart techniques to do this?