1. Chapter 10:(Part 2) Chapter 10: Earthquakes (Part 2)

2. Announcements - Papago Park Fieldtrip Sign up at website. See maps and directions. - Quiz postponed until Monday Volcanoes (Chap. 9) Earthquakes (Chap. 10) - Earth’s Interior (Inter. C) - Midterm 2 Rescheduled for a week from Friday, April 11. Review outline will be posted on the web this coming Monday.

3. Fig. 10.22 W. W. Norton Most earthquakes occur along the margins of tectonic plates

4. Today’s Lecture - Student presentation “Taiwan Earthquake- 9-21-99”- Vilasinee Kongsomboonvech - Introduction to earthquakes Where do Earthquakes occur? Plate tectonic context - Types of earthquake waves Body waves Surface waves (Video simulations)

5. Earthquake “belts” l 95% of energy from earthquakes comes from thin zones marking the edges of tectonic plates

6. Major Earthquake “belts” l Some earthquakes are quite deep (up to 700 km or more) l Deep quakes are found at subduction zones and are confined to downgoing slabs of lithosphere. Active Volcanoes

7. Fig. 10.36c W. W. Norton Gaps in earthquake activity define areas where stress is accumulating. Seismic gaps: Mark likely places for future large earthquakes!

8. Fig. 10.04 W. W. Norton n) shear) EXTENSIONAL STRESS

9. Earthquakes & Plate Tectonics -At divergent plate boundaries, plates move away from each other at constant rates. -Examples: * Red Sea * Mid-Atlantic Ridge. - See video for opening of the Red Sea. Normal Faults (Extensional Stress)

10. Fig. 10.04 W. W. Norton n) shear) COMPRESSIONAL STRESS

11. Earthquake “belts” & faulting styles At convergent plate boundaries, oceannic plates come together forming subduction zones. Example: Peru-Chile Trench.

12. Deep Earthquakes in Subduction Zones

13. Earthquake “belts” & faulting styles Where converging plates are both made of continental crust, they collide, forming mountain belts. Example: Himalayan Mts.

14. Fig. 10.04 W. W. Norton n) shear) Lateral (Shear) Stress

15. Earthquakes & Plate Tectonics -At transform boundaries, plates slip pass each other at constant rates. -Example: San Andreas Fault -At the present rate (~ 1 cm/yr) San Francisco and LA will be neighbors in ~10 million yrs! Transform Faults (Lateral Shear Stress)

17. Fig. 10.00 U.S. Geological Survey

18. Fig. 10.24 W. W. Norton Major Tectonic Environments of Earthquakes Summarizing…

19.  P-waves - Travel faster. - Move through both solids and liquids.  S-waves: Shear waves - Travel slower. - Only travel through solids.  Information carried by these waves is used to: -Locate the focus of the earthquake. -Calculate the earthquake magnitude. - “See” into the Earth’s interior. EARTHQUAKES GENERATE TWO TYPES OF INTERNAL OR “BODY” WAVES

20. Fig. 10.13ab W. W. Norton P-waves: - Compression waves. - Travel fastest. - Move through both solids and liquids.

21. W. W. Norton S-waves: -Shear waves. -Travel slower. - Only travel through solids.

22. Types of Earthquake Waves “Body waves” P-waves (“P” for primary) S-waves (“S” for secondary) Expansion/compression: push/pull motion Shear: side-to-side motion “Surface Waves” travel at the Earth’s surface travel in the Earth’s interior

23. Surface Waves - Cause the most damage. - Two types. * Rayleigh waves: Forward, rolling motion. * Love waves: Side-to-side (lateral) motion - Both are shear waves.

24. Fig. 10.13ef W. W. Norton Love Waves

25. In summary: Types of seismic waves S-wave Surface-wave Motion produced by the different wave types P-wave

26. IN CLASS EXERCISE Observe the following objects as I drop them on the floor in class: - Clay - Rubber Ball - Ice Cube 1) Which of these behaves as a brittle material? 2) As a ductile material? 3) As an elastic material? 4) Which of these material properties accounts for earthquakes?

27. Fig. 10.02 J. Dewey, U.S. Geological Survey Next time: Locating Earthquakes Earthquake magnitudes

28. Human Consequences