The ripples are "built in" but they were easy.

I just duplicated the continent shape, simplified it with ctrl-L, did an offset to push it out, then set the fill to none and changed the line stroke. I repeated that (without the simplify) four times, choosing a longer dashed stroke each time. It was quite easy.

Alternately, I could have made them a linked offset, which would mean that if I changed the continent shape it would have followed, but I haven't figured that out in Inkscape yet...

-Rob A>