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I. Earth Structure A. Inner Core Solid; 1480 km diameter Mostly Ni and Fe Why is it solid even though it’s hot enough to melt any rock? B. Outer Core Plastic/ Liquid; Mostly Ni and Fe C. D. 1990 km thick Mantle 2865 km thick; Made of three distinct layers: 1. Mesosphere Most of Mantle Non-Newtonian substance 2. Asthenosphere Liquid/ slippery Mohorovicic Discontinuity (Moho)- where seismic waves slow down 3. Lower Lithosphere Broken Solid/ brittle Crust Solid; broken into pieces called plates Mostly silica (quartz) rigid, with some flexibility 1. Two types: a. Oceanic Crust More dense of the two; about 5 km thick Basaltic composition (mafic chemistry) 1 b. II. Continental Crust Less dense with more silica; about 35 km thick Granitic composition (felsic chemistry) Do Plates really move? Past/ Indirect Evidence of Plate Tectonics A. Distorted Rock Layers 1. B. Folding & Tilting a. Principle of Original Horizontality c b. Syncline c. Anticline d. Geosyncline b Fossil Evidence 1. Marine reptile found on the East Coast of South America and West Coast of Africa; unable to swim across the open ocean 2. Corals What do corals need to survive? Why are they found in Wisconsin? 3. Ammonites & Belemnites in Montana? 4. Marine shells on top of the Himalayas? III. Present/ Direct Evidence of Plate Tectonics 2 A. Earthquakes B. Displaced structures like fences, buildings, rivers C. Volcanoes IV. So the Plates move, How do they do it? A. V. Convection Currents in the Mantle The Physics of Plate Tectonics A. Forces acting on the crust 1. 2. Tension Forces a. Push or pull away from each other along a single line of motion b. Divergent Boundary/ Rift Compression Forces a. A push towards one another in a single line of motion b. Convergent Boundary Orogeny (mountain building) 1. Subduction Zone 3 3. Shear Forces a. Forces that act in opposite directions along different lines of motion. Like a scissors b. Plates sliding past one another VI. So the Plates move, WHAT Happens now? Joints VS. Faults; Landforms; Earthquakes A. Diastrophism the process by which the earth’s surface is reshaped by movement of the crust B. Jointsare breaks or fractures in bedrock along which NO movement has taken place C. Faults- are breaks or fractures in bedrock along which movement HAS taken place 1. Parts of a Fault a. Footwall- the underlying surface of an inclined fault plane. Can act like a wedge b. Hanging Wall- the overlying surface of an inclined fault plane b a D. Types of Faults 1. Dip-Slip- a fault in which movement is parallel to the dip of the fault surface FYI: Dip is the angle and direction at which a plane is inclined from horizontal 4 a. b. 2. Normal Dip-Slip The hanging wall block has moved DOWN relative to the footwall 1. Caused mostly by TENSION forces 2. Divergent boundary Reverse Dip-Slip The hanging wall block has moved UP relative to the footwall 1. Caused mostly by COMPRESSION 2. Convergent boundary Lateral or Strike-Slip A fault in which the fault block movement is parallel to the strike of the fault surfaces. FYI: Strike is the compass direction of a line by the intersection of an inclined plane with the horizontal plane 3. a. Mostly horizontal displacement, there is little or no vertical movement b. Caused by SHEAR forces Oblique-Slip a fault having both strike-slip and dip-slip components, where plates move away from each other a. Rifting and Sea Floor spreading result from this kind of fault. b. Caused by TENSION forces 5 c. E. Divergent boundary Landforms from Crustal Movement 1. Mountains defined as a mass of rock rising more than 600 meters above the surrounding land a. Fold Mountains usually made mostly of sedimentary rock folded by compression. World’s tallest and most common mountains 1. Examples: Appalachians, Rockies, Alps, Himalayas b. F. Fault-Block Mountains formed by a series of Normal Dip-Slip faults. Some of the greatest mountain Ranges 1. Examples: Sierra Nevada (California), Grand Teton (Wyoming), Wasatch (Utah) When the Earth Shakes- Earthquakes 1. Can be caused by volcanic eruptions, but more often, faulting... a. Faulting the movement of rock along a fault b. Elastic Rebound occurs when tremendous pressure causes plates to move and the rock layers shake back and forth 1. Seismic Waves are waves of vibrations sent out in all directions from the focus 6 2. 3. Where do Earthquakes start? a. Focus the point below the surface where the rocks break and move b. Epicenter the point on the surface, directly above the focus How are Earthquakes measured? a. Seismograph is an instrument that detects, measures, and records the seismic waves produced by earthquakes 1. Operates on Newton’s First Law of Motion 2. Seismogram is the recorded information and looks like a zig zag line a 4. Anatomy of a Wave a. Crest the highest point on a wave b. Trough the lowest point on a wave c. Amplitude refers to the distance from the midpoint to the crest (or trough) d. Wavelength is the distance from the top of one crest to the top of the next or the distance between any successive identical part of the wave 7 b e. 5. Frequency often called Hertz, is the number of vibrations (cycles) per second Types of Seismic Waves a. BODY WAVES: are waves which can travel through the body of the earth 1. Primary Waves AKA P-Wave; are a type of Longitudinal wave. It causes back and forth particle motion; it follows the same direction as the energy transfer 2. a. They are a type of Compressional Wave (sound is this type) b. Will travel through solid, liquid, and gas; must have a medium c. Travels 7.8 –8.5 km per second in the Mantle… 7.2 km per second in oceanic crust... 3.5 km per second in continental crust Secondary Waves AKA S-Wave; With these waves, the particle motion is PERPENDICULAR to the direction of energy transfer a. Transverse or Shear wave b. Will travel only through solid c. Travels 4 - 5 km per second 8 d. b. Moves side to side like a snake SURFACE WAVES: move along the surface of the earth only 1. Surface Waves AKA L-Wave Travel through the crust of the earth and attenuate (gradually disappear); Scientists have found that attenuation occurs more slowly in older rock (like the eastern US, but more quickly in younger rock (western US) a. They’re two main types: Love Waves and Raleigh Waves and they will travel only through solid b. Travels less than 4 km per second c. Moves up and down- causes most damage 9