I was amused to read the following article, and I'll let you read it first to see why, before I comment myself:
Yes, you read that right, a nuclear (well, technically, it would have to be thermonuclear) blast of one million megatons. That's the energy release equivalent of 1,000,000,000,000 - that's one quadrillion - tons, or 2,000,000,000,000,000 pounds, or two quintillion pounds, of TNT.
And all of this was natural according to Dr. John Brandenburg (whom this author has actually met). Well, of course it is. After all, our own sun puts out prodigious amounts of energy every second, and most of it from thermonuclear processes (note, I said most of it). Reading the article, one gets the usual "well this is interesting but there are other scientific models to explain it" response.
Make no mistake, there is evidence here on Earth that natural nuclear reactors formed and operated for a period of time long ago. But these are fission reactors and fission processes would be, to my mind, next to impossible to generate this amount of energy naturally. And fusion processes of this magnitude occurring naturally on a planet... well, that too, does not to my mind compute very easily.
If Brandenburg is correct, that all this is evidence of a gigantic thermonuclear explosion on the red planet aeons ago, then my bet is that it was the product both of technology and deliberate action, in short, it was the occurrence of an act of war.