There are moments when the world we take for granted changes instantaneously — when reality is upended and replaced with the unimaginable. Though we try not to think about it, instability is always lurking, and at any moment, a kind of terrible magic can switch on and scramble our lives.  You may know the feeling. In 1964, it happened to Anchorage, Alaska, and to a woman named Genie Chance. Today, the author Jon Mooallem tells her story — and the story of the biggest earthquake to hit North America in recorded history — using sonic postcards from the past. Guest: Jon Mooallem, author of the book “This Is Chance.” For more information on today’s episode, visit nytimes.com/thedaily