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Unformatted text preview: 1 Modern Plate Tectonics Near Surface Observations to explain Landforms: Mountains, Rift valleys, and Trenches Earthquake and Volcano Locations "Continental Drift" Evidence for Continental Drift (Wegener) Geometrical Ft of continent margins Similarity of fossil record in distant lands Geological features align across ocean basins Sonar for Sea loor Topography reection sound wave Travel distance = (velocity)(elapsed time) Velocity = 1480 m/s ProFle near edge Sea loor Topography rom Kennett (1981) North Atlantic 2 Iceland-Greenland Pacifc Sea Floor note ridges trenches hot spots quake distribution Epicenters 29,0000 quakes 1961-67 Barazangi and Dorman (1969) Arctic Sea Floor Volcano distribution Active volcanoes Plate Tectonics: Concept Earth can be divided into layers based on the strength o the rocks. The outer layer is called the lithosphere . It is cool, strong and much o the deormation in response to stress is elastic or brittle. Below this layer is the asthenosphere , a hotter weak layer that behaves plastically. The lithosphere is divided into regions that move coherently, called plates . Earthquakes occur at plate boundaries, where adjacent plates move in dierent directions. Driving Mechanism: Plates move in response to stresses created by gravity. Dense materials sink into Earth's interior, while less dense materials rise. Density contrasts develop due to heating in the interior and cooling at the surace. 3...
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