A place for my students to get some help in Earth Science
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| Earth Science A place for my students to get some help in Earth Science |
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Thursday, April 19, 2007 Homework for Spring 07 as of 4/19/2007 Chapter page group due 17 343 a two weeks ago 18 362 a two weeks ago 20 406 a Monday 23 Test is on Friday for period 7 and 8 review topics Seismic Station P-Wave Travel Time A 8 min 20 sec B 0 min 31 sec C 12 min 18 sec D 3 min 20 sec 1. Which station is closest to the epicenter? 2. If the P-wave arrived at station D at 09:25:10, what was the origin time of the earthquake, at the epicenter? 3. How far from the epic center were station A and D? Subject: Earth Science TEST REVIEW 1. Evidence of crustal motion a. originally strata (layers) are laid down horizontally – but the layers are often found to be tilted, folded or faulted b. benchmarks indicate changes in elevation i. uplift – rising of crust ii. subsidence – sinking of crust c. fossils of shallow water organisms found on mountains or at great ocean Depth d. earthquake 2. Earthquakes produce seismic waves 3. Mercalli Scale – relative scale, based on observations, measures intensity from I – XII 4. Richter Scale – uses seismograph to determine magnitude (total energy) released by earthquake; each increases in number represents a tenfold increase in energy released 5. Focus – place underground where break or fault occurs 6. Epicenter – location on Earth’s surface, just above the focus where earthquake is felt most strongly 7. primary (P) waves – compressional waves, pushing and pulling, travel faster than S waves can travel through both solids and fluids 8. Secondary (S) waves – shear wave, side to side, cannot travel through liquid 9. ESRT – difference in arrival time between P and S waves, mark interval on paper, slide paper over curves until marks meet the P and S cures, follow edge of paper down to horizontal axis to find distance to epicenter (distance recording station is from epicenter) distance x 103 or 1000 10. Origin Time – Arrival Time – Travel Time = Origin Time 11. To find epicenter – fallow above procedure for 3 seismic recording stations – draw circles – where 3 circles intersect determines the location of the epicenter 12. Layers of the Earth: (properties inferred from behavior of seismic waves) a. Crust – outermost layer; continental crust is granite like rocks, thicker, oceanic crust is basalt like rocks – dense dark mafic b. Mantle – includes most of the Earth’s volume c. Moho – interface (boundary) between crust and mantle d. Lithosphere – crust and upper ridge part of the mantle e. Asthenosphere – plastic like part of the mantle f. Core – mixture of iron and nickel i. outer core – liquid (S waves cannot pass through; P waves slow down) ii. inner core – solid 13. Part of Earth opposite side where earthquake occurs receives P waves but no S waves 14. Surrounding the P wave only zone is a region where neither P nor S waves received (due to refraction/bending at the mantle-core boundary) – this is due to density differences – Shadow Zone 15. Theory of Continental Drift – Earth’s continents have separated and collided as they have moved over Earth’s surface for million of years (ancient continent Pangea – see ESRT page 9) 16. Mid-Oceanic Ridges – encircle Earth oceanic crust is created here – sea/ocean floor spreading – upwelling material from deep in the Earth comes to the surface at the ridges where it spreads apart to make new oceanic crust; youngest crust is near the ridges; oldest crust near the trenches; normal/reversed magnetic polarity is observed in rock records 17. Plate Tectonics – Earth’s surface is composed of approximately a dozen major, rigid Moving crustal plates and some smaller plates - plates move because they are Driven by convection currents in mantle (currents are due to differences in density) ESRT page 5 18. Types of plate boundaries: a. Convergent boundary – plates move towards each other and collide – subduction, dense basaltic oceanic plate dives beneath less dense granite continental plate – forms trenches, if 2 continental plates collide you get mountain building (folding, faulting) as with Andes or Himalayas b. Transform boundary – plates slide past one another produces many earthquakes; example San Andreas Fault in California c. Divergent boundary or Rift – where plates moving apart as at mid-oceanic ridges 19. Convection cells bring material to the surface at ocean ridges and pull it back into Earth at the trenches 20. Subduction Zone – area where crust is being pulled down into the mantle 21. Zones (belts) of crustal activity – mountain building, volcanoes, and earthquakes are related events ( occur due to internal pressure within the earth) 22. Ring of Fire – surrounds Pacific Ocean 23. Hot Spots – hot plumes of magma pierce the crust as plates move over – results in a chain of volcanoes of different ages (example Hawaiian Island) posted by James | 9:38 AM |
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