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Unformatted text preview: 1 Plate Tectonics and Plate Tectonics and Earthquakes Earthquakes Chapter 3 Chapter 3 GEOL 171 Earthquakes and Natural Disasters Plate Tectonics and Earthquakes Gujarat, India, January 26, 2001: Major earthquake great natural disaster Event so destructive that outside help is needed 20,103 people killed, deadliest natural disaster of 2001 Turkey , August & November, 1999: Numerous building failures (similar to India) More than 19,000 people killed tectonic (lithospheric) plate Plate Tectonics and Earthquakes Lateral movement (> 250 my) Tectonic cycle Plate Tectonics - Tectonic cycle Melted asthenosphere flows upward as magma Cools to form new ocean floor (lithosphere) New oceanic lithosphere (slab) diverges from zone of formation atop asthenosphere (seafloor spreading) When slab of oceanic lithosphere collides with another slab, older, colder, denser slab subducts under younger, hotter, less dense slab Subducted slab is reabsorbed into the mantle Cycle takes on order of 250 million years Plate Tectonics Lithosphere of Earth is broken into plates Plate Tectonics: Study of movement and interaction of plates Zones of plate-edge interactions are responsible for most earthquakes, volcanoes and mountains Divergence zones Plates pull apart during seafloor spreading Transform faults Plates slide past one another Convergence zones Plates collide with one another 2 Tectonic Plates & Plate Tectonics Plate boundaries: divergent, convergent, transform Development of the Plate Tectonics Concept 1620: Francis Bacon noted parallelism of Atlantic coastlines of Africa and South America Late 1800s: Eduard Suess suggests ancient supercontinent Gondwanaland (South America, Africa, Antarctica, Australia, India and New Zealand) 1915: Alfred Wegeners book supports theory of continental drift all the continents had once been supercontinent Pangaea, and had since drifted apart Development of the Plate Tectonics Concept Theory of continental drift was rejected because mechanism for movement of continents could not, at the time , be visualized 20 th century: study of ocean floors provided wealth of new data and breakthroughs in understanding Lithosphere moves laterally Continents are set within oceanic crust and ride along plates Theory of plate tectonics was developed and widely accepted by the mid-1960s Evidence of Plate Tectonics 1. Seafloor magnetization 2. Earthquake locations 3. Deep earthquakes defining subduction zones 4. Young ages of ocean basins 5. Hot-spot tracks 6. Thickness of marine sediments / seafloor depth 7. Locations of mid-ocean ridges and trenches 8. The shape of the continental outlines 9. Changing positions of continents Earths Magnetic Field Earths magnetic field acts like giant bar magnet, Magnetic pole axis is now inclined 11 from vertical (tilt has varied with time) so that magnetic poles do not coincide with geographic poles (but...
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- Spring '08