When I was able to read it, I just didn't see the circular features that you were seeing. It just seemed like you picked a couple of peaks randomly as the center points and drew circles around those. Parts of the circle just happened to coincide with a few features, but, try as I might, I didn't see the rounded structures typical of an impact crater. I take it the images are from Google Earth. Do you have some pics that are a higher resolution?
Finally, wouldn't two impacts of that magnitude wipe out pretty much every living thing except microbes? The Chixulub crater, believed to have been the death-knell of the dinosaurs, is about 170 km wide. Imagine what an impact would do after making a crater 500 km wide! I don't think we'd be here to talk about it.
~ Woody Allen