It lurks in the corner of our imagination, almost beyond our ability to see it: the possibility that a tear in the fabric of life could open up without warning, upending a house, a skyscraper, or a civilization. Today, nine out of ten Americans live in places at significant risk of earthquakes, hurricanes, tornadoes, terrorism, or other disasters. Tomorrow, some of us will have to make split-second choices to save ourselves and our families. How will we react? What will it feel like? Will we be