The title of this book is wrong, in the sense there is very little actual calculation done. In general the book is a description of human and natural (rather than mathematical) catastrophes: the majority of the pages deal with human disasters. Historic volcanic eruptions, hurricanes, mudslides, floods, tornadoes, plagues, earthquakes and manmade economic disasters are described in nonmathematical detail. Many historical references are used, which made the book very interesting.
However, if you are looking for a mathematical analysis of catastrophes beyond that at the level of the general reader, you will find little of that here. There are a few advanced equations, but they are so sparse that the impression is that they were inserted as afterthoughts. The mathematics that appears most often is basic probability and simple predictions based on past events. Nevertheless, I found it an excellent history of catastrophes in the history of the planet, most of which involved the deaths of large numbers of humans.
Charles Ashbacher splits his time between consulting with industry in projects involving math and computers, teaching college classes and co-editing The Journal of Recreational Mathematics. In his spare time, he reads about these things and helps his daughter in her lawn care business.