feather 2D model edges? mask?

[AsheMosterMashe]

I modelled a shockwave effect (just some open faces, no floor) with a scrolling texture applied, but I need the edges of those planes to feather out (where I've painted in black).
The scrolling texture is additive so if I could just apply a black blur on the same faces, using the same UVs I'd be set. I just can't bake it into the existing material because I don't want the feathering to scroll too.
Is there any way for me to do this? either as a mask to my material or just as a second material applied to the same faces with Blender?

 

[AsheMosterMashe]

managed to find exactly what I was looking for, by using a detail texture with the black/white mask for transparency