How do i bolt my 2 bookshelves to my wall?

I have been meaning to ask this for a while now. i am on the New Madrid fault, and there has been some recent activity. Something is telling me that an earthquake is coming. My gut is has never been wrong, and I don't expect it to start now. My shelves would be featherweight in an earthquake. And the stuff I have on there is irreplaceable. It's items I have taken years to collect. And your obvious books. =)