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Transcript
The Earth’s Internal Properties I. Seismic Waves A. = Earthquake-generated waves traveling through the Earth’s interior B. Give us clues to the composition of the Earth C. Types of Seismic Waves 1. Surface waves – travel on the Earth’s surface 2. Body waves – travel through the Earth’s interior Body waves a. P-waves (primary waves) Compress and expand rock Are the fastest of all seismic waves First waves to register on seismograph Body waves b. S-waves (secondary waves) Vibrate up and down Second waves to register on a seismograph Seismograph = Device which measures seismic waves II. Earth’s internal layers Geologists did research with seismic waves Concluded that the Earth’s interior is layered. Earth’s internal layers Earth’s internal layers A. The Core1. Composed mostly of iron and nickel 2. Inner Core very hot solid Fe & Ni due to high pressure of the Earth The Core (continued) 3. Outer Core less pressure from the earth liquid Fe & Ni Flow in the outer core generates an electric current that powers the Earth’s magnetic field. B. The Mantle Rocky layer About 3000km thick 1. Two parts of mantle a. Lower mantle b. Upper mantle – two sections b. Upper mantle i. Asthenosphere - behaves in a semi-fluid manner b. Upper mantle ii. Lithosphere- rigid and brittle C. The Crust 1. 2. Uppermost portion of the lithosphere Two types of crust a. Oceanic crust - about 10 km thick C. The Crust b. Continental crust – about 20-60 km thick III. Theory of Continental Drift A. Belief that the earth is a dynamic planet with the continents in constant motion (i.e. continents are moving) III. Theory of Continental Drift B. All continents once joined together into supercontinent called Pangea (meaning = all land) C. Theory formulated by Alfred Wegener III. Theory of Continental Drift D. Evidence that supports theory = 1. Geologic (rock) 2. Biologic (life) 3. Climatological (past weather) 4. Continental Shelves fit together very well Tectonic Plates = moving sections of the lithosphere on which continents lie IV. Faults Fault = a fracture along which visible displacement can be detected on one side relative to the other. B. Types of faults 1. Footwall-Fig 23.17 (“one on bottom”) A. Footwall B. Types of faults 2. Hanging wall- Fig 23.17 (“one on top”) V. Vertical movement along a fault 1. Reverse Fault- Fig 23.18- Footwall down Examples: Rocky Mountains Canadian Rockies Appalachian Mts. V. Vertical movement along a fault 2. Normal Fault- Fig 23.19- Footwall up VI. Horizontal movement along a fault boundary (Fig. 23.22) A. Transform-fault boundary – plates are sliding past one another (Figs. 23.27 & 28) E.g. San Andreas fault in California ★ Earthquakes caused by sheering forces B. Divergent Boundaries 1. two plates are moving apart (Fig. 23.23) Plate A Plate B 2. Creates rift valleys – large spreading valleys at fault line 3. Creates sea floor spreadinga rift valley on sea floor 4. Caused by tensional forces B. Divergent Boundaries C. Convergent Boundaries 1. Two plates move towards each other (Fig 23.24) Plate A Plate B 2. Leads to subduction- one plate (usually oceanic crust) goes beneath the other (continental crust). Caused by compressional forces C. Convergent Boundaries C. Convergent Boundaries Ex: Andes Mountains in S. America (Still growing because of subduction) 3. ★Common place to find volcanoes Ex: Cascade Range (Mt. St. Helens, Mt. Rainier…) Tectonic Plate Movement Major Tectonic Plates