1. EXPLORING EARTH’S INTERIOR Chapter 14

2. Seismic rays are refracted away from the normal as they penetrate the earth, which causes them to bend, because each lower layer in the earth’s mantle becomes progressively more dense due to the weight of overlying rock. High density and high strength Low density and Lower strength i r Seismic ray Angle of incidence i < angle of refraction r

3. S-wave paths through Earth’s interior. Focus S-wave shadow zone 0° 105° Inner core Mantle Outer core S wave shadow zone between 5 and 105 degrees Reveals the earth’s liquid outer core

4. The pattern of P-wave paths through Earth’s interior. Focus P-wave shadow zone 0° 105° 142° P wave shadow zone between 105 and 142 degrees Reveals the earth’s solid inner core

7. In order for rocks to melt within the earth, the melting curve for rock must be to the left of the geotherm (the earth’s temperature with depth). Note that this occurs only in the outer core and asthenosphere. It is even more interesting to consider that the melting curve for rock in this figure is for a wet asthenosphere. If the asthenosphere were dry, the melting temperature would be above the geotherm, and upwelling mantle would not melt.

8. Focus Solid inner core Liquid outer core Mantle Seismographic stations Seismic tomography uses the travel times from many earthquakes to create three- dimensional images of Earth’s interior.

9. North America Africa

10. North America Africa A tomographic section reveals a mantle plume beneath South Africa,…

11. North America Africa …and the remnants of the Farallon Plate under North American Plate. A tomographic section reveals a mantle plume beneath South Africa,…

12. 70 km

13. Near Earth’s surface, hot rocks in the asthenosphere slow S waves.

14. 200 km

15. Moving deeper, we see the cold lithosphere of stable continental cratons and warmer asthenosphere beneath ocean basins.

16. 500 km

17. Deeper in the mantle, the features no longer match the continental positions.

18. 2800 km (near mantle-core boundary)

19. Colder regions around the Pacific may be the “graveyards” of sinking lithospheric slabs.