1. Earthquakes and Earth’s Interior
GEOL: CHAPTER 8
Earthquakes and Earth’s Interior

2. Learning Outcomes LO1: Explain Elastic Rebound Theory
LO2: Describe seismology
LO3: Identify where earthquakes occur, and how often
LO4: Identify different seismic waves
LO5: Discuss how earthquakes are located

3. Learning Outcomes, cont.
LO6: Explain how the strength of an earthquake is measured
LO7: Describe the destructive effects of earthquakes 
LO8: Discuss earthquake prediction methods
LO9: Discuss earthquake control methods

4. Learning Outcomes, cont.
LO10: Describe Earth's interior
LO11: Examine Earth's core
LO12: Examine Earth's mantle
LO13: Describe Earth's internal heat
LO14: Examine earth's crust

5. Earth’s Interior
Crust
Mantle
Outer core
Inner core

6. Figure 8.18 Earth’s Internal Structure The inset shows Earth’s outer part in more detail. The asthenosphere is solid but behaves plastically and flows.

7. Seismic Waves and Earth’s Interior
P-wave and S-wave velocity determined by density and elasticity of material
S-waves don’t travel through liquids
Seismic waves change velocity and direction when enter material with different density or elasticity (refraction)

8. Seismic Waves and Earth’s Interior, cont.
Some waves are reflected
Calculate depths of boundaries
Discontinuity: significant change in materials or their properties

9. Figure 8.19 Refraction and Reflection of Seismic Waves Refraction and reflection of P-waves as they encounter boundaries separating materials of different density or elasticity. Notice that the only wave ray not refracted is the one perpendicular to boundaries.

10. Figure 8.20 Seismic Wave Velocities Profiles showing seismic wave velocities versus depth. Several discontinuities are shown, across which seismic wave velocities change rapidly.

11. Figure 8.20 Seismic Wave Velocities Profiles showing seismic wave velocities versus depth. Several discontinuities are shown, across which seismic wave velocities change rapidly.

12. Figure 8.20 Seismic Wave Velocities Profiles showing seismic wave velocities versus depth. Several discontinuities are shown, across which seismic wave velocities change rapidly.

13. The Core
P-wave velocity decreases at a depth of 2,900 km: core-mantle discontinuity
P-wave shadow zone
Weak P-wave energy does penetrate the shadow zone: from solid inner core
S-wave shadow zone: shows the outer core is liquid, because S-waves can’t travel through liquids

14. Figure 8.21 P-Wave and S-Wave Shadow Zones

15. Figure 8.21 P-Wave and S-Wave Shadow Zones

16. Figure 8.21 P-Wave and S-Wave Shadow Zones

17. Core Density and Composition
16.4% Earth volume
~33% of mass
Outer core: 9.9 to 12.2 g/cm3
Earth center: pressure 3.5 million times of surface
Outer core: iron, sulfur, silicon, oxygen, nickel, potassium
Inner core: iron and nickel

18. Earth’s Mantle Moho: discontinuity about 30 km deep Asthenosphere:
P- and S-waves slow down
Plastic
Magma generation
Lithospheric plates ride across it
3.3 to 5.7 g/cm3; probably periodotite

19. Figure 8.22 Seismic Discontinuity Andrija Mohorovičić studied seismic waves and detected a seismic discontinuity at a depth of about 30 km. The deeper, faster seismic waves arrive at seismic stations first, even though they travel farther. This discontinuity, now known as the Moho, is between the crust and mantle.

20. Earth’s Internal Heat Geothermal gradient: 25ºC/km
Greater in active volcanic regions
Most heat generated by radioactive decay
Regions of equilibrium temperature
Base of crust: 800ºC to 1200ºC
Core-mantle boundary: 2,500ºC -5,000ºC

21. Continental Crust Granitic composition
2.5 to 3.0 g/cm3; average = 2.7 g/cm3
20 to 90 km thick; average = 35 km thick
Thickest under large mountain ranges

22. Oceanic Crust Gabbro overlain by basalt Average density = 3.0 g/cm3
5-10 km thick
Thinnest at spreading ridges