ch3_tectonics

ch3_tectonics - Plate Tectonics and Earthquakes Natural...

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Unformatted text preview: Plate Tectonics and Earthquakes Natural Disasters, 6 th edition, Chapter 3 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 Figure 3.1 Turkey , August & November, 1999: Numerous building failures (similar to India) More than 19,000 people killed Amos Nur, earthquakesandarchaeology.smugmug.com 1700 Cascadia Earthquake Magnitude of 8.7 to 9.2 - carbon dating of local tsunami deposits. Seismic x-section cascadia here ... Andrew Calvert, 2004, Nature 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, colder, denser slab subducts under less dense slab Subducted slab is reabsorbed into the mantle Cycle takes on order of 250 million years Plate Tectonics Tectonic cycle: Figure 3.2 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 Plate Tectonics Lithosphere of Earth is broken into plates separated by: divergence zones, transform faults, convergence zones Figure 3.3 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 Theory of continental drift was rejected because mechanism for movement of continents could not, at the time , be visualized Earth's magnetic f i eld 1950s, magnetometers adapted for marine from World War II submarine detection. Find odd magnetic variations across the ocean f l oor (basalt Fe rich). Noticed by Icelandic mariners late 1700s. Earths Magnetic Field Earths magnetic field acts like giant bar magnet , with north end near the North Pole and south end near the South Pole Magnetic pole axis is now inclined 11 o from vertical (tilt has varied with time) so that magnetic poles do not coincide with geographic poles (but are always near each other) Inclination of magnetic lines can also be used to determine at what latitude the rock formed Magnetic field is caused by dynamo in liquid outer core: Movements of iron-rich fluid create electric currents that generate magnetic field Figure 3.4 Earths Magnetic Field...
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This note was uploaded on 03/22/2009 for the course GEOL 171 taught by Professor Tsoflias during the Spring '08 term at Kansas.

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ch3_tectonics - Plate Tectonics and Earthquakes Natural...

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