I have one site that I don't really do a whole lot with,, it's been tipping along at 200 or visits per day. But yesterday I noticed a big jump in search traffic, like 10 times what I would normally get, and all aimed at a mixture of my sites pages. Like I said, It's very strange and I have never had this before. Stats...
Look at the landing page and what people were searching for. ie if you have a domain like (name natural disaster) that might be whats causing it.
That's happened to me before not on the same level but say instead of getting 10 visits a day I got 150 it turns out I wrote about a festival that was happening on a specific date and as that day came my traffic spiked.