Realistically, what should you learn from this book? Almost no one reads a scientific monograph from cover to cover; and, even when they do, there can be so much focus on details that it's easy to lose track of what's important. Thus, in this chapter I review what a century of research has taught scientists about deep earthquakes, and then discuss some cultural issues that surround the business that is deep earthquake research.

What we know and what we don't know

What we have learned in the last 100 years

What do we know today about deep earthquakes that we didn't know when Fusakichi Omori was pondering the peculiarities of the 21 January 1906 Japanese earthquake (see the Preface)? Omori was then well into his career and, since he died in 1923, didn't survive to see much of the progress that this book chronicles. It is interesting to imagine what Omori and Harold Jeffreys (1891–1989) might have thought about this book. Jeffreys, of course, had a long and distinguished career in geophysics, as he published his first scientific paper in 1915, his last paper in 1987 (Jeffreys and Shimshoni, 1987), and grappled with several of the research questions that this book chronicles. Each chapter in this book presents information that would have intrigued Omori and about which Jeffreys would have had some firm opinions. What have we learned in 100 years?