Book contents
- Frontmatter
- Contents
- Preface
- I Background and introductory material
- 1 The big, the bad, and the curious
- 2 What, where, how, and why?
- 3 The history of deep earthquakes
- II Properties of intermediate- and deep-focus earthquakes
- III The mechanism of deep earthquakes
- IV Why bother about deep earthquakes?
- V Geographic summary
- Earthquake index
- Index
2 - What, where, how, and why?
Published online by Cambridge University Press: 05 August 2013
- Frontmatter
- Contents
- Preface
- I Background and introductory material
- 1 The big, the bad, and the curious
- 2 What, where, how, and why?
- 3 The history of deep earthquakes
- II Properties of intermediate- and deep-focus earthquakes
- III The mechanism of deep earthquakes
- IV Why bother about deep earthquakes?
- V Geographic summary
- Earthquake index
- Index
Summary
What are deep-focus and intermediate-focus earthquakes?
When we call an earthquake “deep,” what do we mean? As we shall see, there is surprisingly little agreement about this among seismologists. However, in this book I use these definitions:
• A shallow or shallow-focus earthquake is any earthquake with a believable reported focal depth less than 60 km;
• An intermediate-focus, intermediate-depth, or intermediate earthquake is any earthquake with a believable reported focal depth equal to or greater than 60 km but less than 300 km;
• A deep-focus earthquake is any earthquake with a believable reported focal depth of 300 km or more;
• A deep earthquake is any deep-focus or intermediate-focus earthquake, i.e., a quake with a believable reported focal depth of 60 km or more.
Although it is confusing for “deep-focus” and “deep” to specify distinctly different depth categories, it is often desirable (as with the title of this book) to specify intermediate- and deep-focus earthquakes together. Since about 1970 a few scientists have called them “mantle” earthquakes instead of “deep” earthquakes (e.g., Isacks and Molnar, 1971). This is misleading since not all shallow-focus earthquakes occur within the crust; e.g., nearly all oceanic intraplate earthquakes are shallow but occur in the mantle. Finally, there are now already hundreds of published papers which used “deep earthquake” to specify both deep-focus and intermediate-focus events.
- Type
- Chapter
- Information
- Deep Earthquakes , pp. 30 - 52Publisher: Cambridge University PressPrint publication year: 2006