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Dynamic Earth

Dynamic Earth. Part 1. Uplift. Rising of the Earth’s crust Evidence Fossils of seashells in rocks on a mountain Observing sedimentary rock layers. Normal Layers. Tilted Layers. Folded Layers. Faulted Layers. I. Uplift. Part 2. Earthquake.

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Dynamic Earth

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  1. Dynamic Earth

  2. Part 1. Uplift • Rising of the Earth’s crust • Evidence • Fossils of seashells in rocks on a mountain • Observing sedimentary rock layers

  3. Normal Layers Tilted Layers Folded Layers Faulted Layers I. Uplift

  4. Part 2. Earthquake • Vibrating, shaking or rapid motion of the Earth’s crust • Terms • Focus – point where the break (fault) happens • Epicenter – point on surface directly OVER the focus; EQ is strongest here

  5. II. Earthquake • Intensity – measure of the damage caused by EQ • Magnitude – totalenergy released by EQ • SeismicWaves – energy waves sent through Earth during an EQ • Seismograph – used to record seismic waves and determine the magnitude of the EQ

  6. II. Earthquake

  7. II. Earthquake • Richter Scale – used to measure energy of an EQ • Each number shows increase of 10 times

  8. Earthquake • Seismic Waves • P-Waves – primary waves; fastest moving; travel through solids AND liquids; particles move in same direction of travel • S-Waves – shear or secondary waves; slower than P; CANNOT travel through liquids; particles move in right angles to direction • The more dense the material, the faster the waves move

  9. II. Earthquake

  10. Prepared by Mr. DeMarco Notice the vertical axis This represents TIME (in minutes!) Let’s enlarge a small section

  11. Prepared by Mr. DeMarco Between each minute, we notice that there are 3 segments. If there are 60 seconds in a minute, each one of these segments must be ________seconds. 20

  12. Prepared by Mr. DeMarco What would this time be? 2 minutes, 20 seconds

  13. Prepared by Mr. DeMarco Notice the horizontal axis This represents DISTANCE (in thousands of Kilometers!) Let’s enlarge a small section

  14. Prepared by Mr. DeMarco 1,000km 2,000km 1,200km 1,800km So what would this distance be? 1,400km 1,600km Fill these in... 5,400km

  15. Prepared by Mr. DeMarco There are also two curves on this chart that display the way different earthquake waves behave.

  16. Prepared by Mr. DeMarco S-Wave P-Wave

  17. This chart can be used for answering many different questions! Let's try a few examples How long does it take an S-Wave to travel 5,000km? Go to the chart! Prepared by Mr. DeMarco

  18. Prepared by Mr. DeMarco

  19. Another example... The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be? Go to the chart! Prepared by Mr. DeMarco

  20. Prepared by Mr. DeMarco 3,600km

  21. Another example... I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be? Go to the chart! Prepared by Mr. DeMarco

  22. Prepared by Mr. DeMarco Slide your scrap paper up until the tick marks match up with the curves… 5,400km Mark off 7 minutes on scrap paper…

  23. Part 3. Finding Epicenter Distance • P-Wave arrives at 3:21 • S-Wave arrives at 3:25 • Difference in arrival times = 4 minutes • Using EQ chart… • Epicenter Distance = 2.6x103 = 2600 km

  24. Part 4. Finding Origin Time • Origin Time – when EQ happens • Find Epicenter Distance first (2600 km) • Use EQ chart to find a P-Wave travels 2600 km in 5 minutes • P-Wave Time – Travel Time = Origin Time • 3:21 – 5 minutes = 3:16 Origin Time

  25. IV. Finding Origin Time • Example • P-Wave arrived @ 5:35 • S-Wave arrived @ 5:41 • What time did EQ happen? • Difference = 6 minutes • Epicenter Dist = 4400 km • P-wave Travel Time = 7 min 40 sec • 5:35:00 – 00:07:40 = ? • 5:27:20

  26. V. Locating an Epicenter • 3 seismographs are needed to locate an epicenter.

  27. A B Epicenter C V. Locating an Epicenter • Example • Station A = 2500 km • Station B = 1500 km • Station C = 500 km

  28. Part 1. Layers of Earth • Using Seismic waves, models have been made for Earth’s interior • Between 5 and 60 miles there is a sudden increase in speed of the waves • So density increases between 5 and 60 miles • This boundary is called Mohorovicic Discontinuity (Moho)

  29. Layers of Earth • Crust (Lithosphere) • Lessdense rock above the Moho; 5-60 miles thick • Continental Crust – THICKEST under continents; less dense; granite rock • Oceanic Crust – THINNEST under oceans; more dense; basalt rock

  30. Layers of Earth

  31. Layers of Earth • Mantle • More dense rock below the Moho; extends to 2900 km deep • Asthenosphere – upper level of mantle; moves and contains convection currents • Stiffer mantle – more dense and solid under the asthenosphere

  32. Layers of Earth • Core • Outer Core – probably liquid; S-Waves do NOT travel through this region • Inner Core – very center of Earth; acts like a solid due to extreme pressure • Core mainly made of iron and nickel • Learned from studying meteorites

  33. Layers of Earth

  34. Densities (continental < oceanic) Convection Currents Pressure (1atm is pressure at surface) Temperature Melting Occurs HERE! Depth in km

  35. What is the pressure found at 3000 km? 1.5 million atm

  36. What is the temperature found at 2000 km? 4200 ° C

  37. Part 2. Shifting of the Crust • Continental Drift Theory • Proposed by Alfred Wegner in 1912 • Continents had been moving for millions of years

  38. Shifting of the Crust • Rock layers match on edges of continents • Evidence • Continents seem to fit together (Pangea) • Similar fossils found along continental edges • Did NOT explain WHY they moved

  39. Shifting of the Crust • Sea Floor Spreading • Chain of underwatermountains found near center of Atlantic Ocean (mid-Atlantic Ridge) • Rock at center is YOUNGER than outside rock • Higher temps found in rock along ridge

  40. Shifting of the Crust

  41. Shifting of the Crust • Center of ridge is a deep, steeply walled valley • Molten rock is pushed to surface, causing sea floor to spread (widen) as ocean is pushed apart along the ridge

  42. Shifting of the Crust • Paleo-magnetism – the switching of the magnetic poles follows a pattern that matches up on each side of the ocean ridges

  43. Shifting of the Crust

  44. Part 3. Plate Tectonics • Plates – rigid moving pieces that make up the crust of Earth; 12 major plates • As plates move, continents are carried with them • Plates are moved by convection currents within upper mantle (asthenosphere)

  45. Plate Tectonics

  46. Plate Tectonics • Plate Boundaries • Types • Divergent – plates moving away from each other; mid-ocean ridges • Convergent – plates colliding with one plate sinking under the other; ocean trenches (subduction) • Transform – plates sliding past each other; San Andreas Fault • Most active areas of the crust (location of most EQs, volcanoes and mountain building)

  47. Plate Tectonics

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