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Chapter 10:(Part 2) Chapter 10: Earthquakes (Part 2)
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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.
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Fig. 10.22 W. W. Norton Most earthquakes occur along the margins of tectonic plates
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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)
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Earthquake “belts” l 95% of energy from earthquakes comes from thin zones marking the edges of tectonic plates
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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
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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!
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Fig. 10.04 W. W. Norton n) shear) EXTENSIONAL STRESS
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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)
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Fig. 10.04 W. W. Norton n) shear) COMPRESSIONAL STRESS
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Earthquake “belts” & faulting styles At convergent plate boundaries, oceannic plates come together forming subduction zones. Example: Peru-Chile Trench.
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Deep Earthquakes in Subduction Zones
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Earthquake “belts” & faulting styles Where converging plates are both made of continental crust, they collide, forming mountain belts. Example: Himalayan Mts.
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Fig. 10.04 W. W. Norton n) shear) Lateral (Shear) Stress
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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)
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Fig. 10.00 U.S. Geological Survey
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Fig. 10.24 W. W. Norton Major Tectonic Environments of Earthquakes Summarizing…
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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
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Fig. 10.13ab W. W. Norton P-waves: - Compression waves. - Travel fastest. - Move through both solids and liquids.
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W. W. Norton S-waves: -Shear waves. -Travel slower. - Only travel through solids.
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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
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Surface Waves - Cause the most damage. - Two types. * Rayleigh waves: Forward, rolling motion. * Love waves: Side-to-side (lateral) motion - Both are shear waves.
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Fig. 10.13ef W. W. Norton Love Waves
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In summary: Types of seismic waves S-wave Surface-wave Motion produced by the different wave types P-wave
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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?
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Fig. 10.02 J. Dewey, U.S. Geological Survey Next time: Locating Earthquakes Earthquake magnitudes
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Human Consequences
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