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Chapter 10: Earthquakes (Part 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. - Most earthquakes occur along the margins of tectonic plates Fig. 10.22 W. W. Norton 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) Earthquake “belts” 95% of energy from earthquakes comes from thin zones marking the edges of tectonic plates Major Earthquake “belts” Some earthquakes are quite deep (up to 700 km or more) Deep quakes are found at subduction zones and are confined to downgoing slabs of lithosphere. Active Volcanoes Gaps in earthquake activity define areas where stress is accumulating. Fig. 10.36c W. W. Norton Seismic gaps: Mark likely places for future large earthquakes! n) Fig. 10.04 EXTENSIONAL STRESS W. W. Norton shear) Earthquakes & Plate Tectonics Normal Faults (Extensional Stress) -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. n) Fig. 10.04 COMPRESSIONAL STRESS W. W. Norton shear) Earthquake “belts” & faulting styles At convergent plate boundaries, oceannic plates come together forming subduction zones. Example: Peru-Chile Trench. Deep Earthquakes in Subduction Zones Earthquake “belts” & faulting styles Where converging plates are both made of continental crust, they collide, forming mountain belts. Example: Himalayan Mts. n) Fig. 10.04 Lateral (Shear) Stress W. W. Norton shear) Earthquakes & Plate Tectonics Transform Faults (Lateral Shear Stress) -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! Fig. 10.00 U.S. Geological Survey Summarizing… Fig. 10.24 W. W. Norton Major Tectonic Environments of Earthquakes EARTHQUAKES GENERATE TWO TYPES OF INTERNAL OR “BODY” WAVES 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. P-waves: - Compression waves. Fig. 10.13ab - Travel fastest. - Move through both solids and liquids. W. W. Norton S-waves: -Shear waves. -Travel slower. - Only travel through solids. W. W. Norton Types of Earthquake Waves “Body waves” travel in the Earth’s interior P-waves (“P” for primary) Expansion/compression: push/pull motion S-waves (“S” for secondary) Shear: side-to-side motion “Surface Waves” travel at the Earth’s surface Surface Waves - Cause the most damage. - Two types. * Rayleigh waves: Forward, rolling motion. * Love waves: Side-to-side (lateral) motion - Both are shear waves. Love Waves Fig. 10.13ef W. W. Norton In summary: Types of seismic waves Motion produced by the different wave types P-wave S-wave Surface-wave 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? Fig. 10.02 J. Dewey, U.S. Geological Survey Next time: Locating Earthquakes Earthquake magnitudes Human Consequences