Lecture 21 more earthquakes

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 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 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) 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 (~ 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 [...]... 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... 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... - 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