Making Fractal lines in GIMP

[Redrobes]

Same process but cut out the sea and paste back on instead of the land so that the glow goes into the land instead.

I think you need to do this on layers and mask each region out one by one and add in the glow a little at the end. But yeah its basically take the shape, blur it, mask out off the shape so that your left with just the blur that went into it and put in as a layer. Maybe multiply it with a constant color like red to get a red glow.