Being in Oregon, where a big one is expected in the next couple hundred years, I am interested in earthquakes. Oregon's expected one was not mentioned in the book, however. 
 The subtitle makes it sound like the book is about San Francicso, 1906. And half is, directly. The rest indirectly as Winchester explains New Geology, plate tectonics, and the formation of continents. He manages to make this science mostly understandable to lay readers like me. He tells of previous earthquakes and some that followed, some on the San Andreas Fault and others elsewhere. 
 When he gets to San Francisco, there is a mix of description, history and memoir, only occasionally becoming a string of similar quotations on the same theme. Most citations build either the chaos or the attempts at controlling the chaos. Then there are the insurance companies, some paying up and others making loopholes. An aspect I'd not thought about before is the problem of Chinese immigrants trying to prove family links when records have been destroyed. 
 Rarely do I read all content footnotes, but here I did. Some were humorous asides; some were bits of interesting history that didn't quite relate to the ongoing narrative. Almost all were interesting.