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Earth’s Dynamic Crust

Earth’s Dynamic Crust. Aim: What is meant by “Dynamic Crust” and what evidence can we observe to support it? Do Now Open your review books to p. 245 In Figure 12-1 Diagram D label layers 2,3,4, and 5 using your scheme for sedimentary rock identification (ESRT)

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Earth’s Dynamic Crust

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  1. Earth’s Dynamic Crust • Aim: What is meant by “Dynamic Crust” and what evidence can we observe to support it? • Do Now • Open your review books to p. 245 • In Figure 12-1 Diagram D label layers 2,3,4, and 5 using your scheme for sedimentary rock identification (ESRT) • Which of these numbered layers do you think is the oldest, why? HW: R+H 244-245, A+E 1-8

  2. Uniformitarianism – The same processes that shaped the earth in the past are the same processes shaping the earth today. • Original Horizontality - sedimentary rocks and extrusive igneous rocks form in flat, horizontal layers called normal strata. • Superposition – the oldest rock layers will be the deepest in the Earth (upset only by overturning and thrust faults) Normal Strata

  3. Convection currents in the mantle put stress on the crust causing it to move and crack. Cracks join up to create crustal plates.

  4. Earth’s outer shell is layers of solid rock called the crust. • Because of the constant stress put on the crust it becomes cracked (creating fault lines and crustal plates). • When there is movement along a fault an earthquake is produced which can cause volcanic activity or mountain building. • These fault lines on the earth are known as “zones of crustal activity, earthquake belts or earthquake zones”

  5. Crustal Disturbances- are the result of convection currents in the mantle constantly putting stress on the crust (pushing and pulling). • Types of Stress: • 1. Compression – two strata moving towards one another, causes reverse faults • 2. Tension – two strata moving away from one another, causes normal faults • 3. Shearing- two strata moving laterally with respect to one another, causes lateral faults

  6. Rock Layers which are no longer show original horizontalitiy are referred to as disturbed • There are three kinds of disturbed strata • Folded – bent or curved layers Syncline Anticline Occurs Because Rock Types Are Ductile – Bend Easily and are being compressed.

  7. 2. Faulted Strata – a break has occurred in the horizontal layer Foot wall is underneath the fault. Hanging wall rests on the fault. This occurs because the rocks are brittle or easily broken. This is tension (although could also compress reversing the fault.

  8. 3. Tilted Strata – rocks appear diagonal or slanted Caused by compression.

  9. All three of these types of disturbed strata are evidence for crustal movement • There is one more piece of evidence… • EurypterusRemipes(and other fossils) • Marine fossil found on top of mountains in NYS • Shows evidence of crustal uplift. • Shallow water fossils at deep ocean depths.

  10. So… • What do you think we mean when we say “Dynamic Crust” • What have we learned about today that can support this?

  11. 3-14-12 Aim: What is an Earthquake? Do Now: • 1 What is an earthquake? • 2. . What is the difference between P,S and L waves? HW: Finish Lab.

  12. Parts of an Earthquake • Fault – crack along which movement occurs. • Focus- point of origin where initial motion takes place. • Epicenter- point on surface directly above focus. • Seismic waves- shock or vibrational waves coming out of the focus or epicenter.

  13. Seismic Waves- produced by an earthquake. P-Waves • Also called primary waves or compressional waves • Faster so first to arrive • Travel through all materials • Comes from the focus S-Waves • Also called secondary waves or shear waves because they cause most of the shaking • Slower so always arrive after P-Waves • Travel through SOLIDS ONLY • Comes from the focus Surface Waves or L-waves • Slowest kind of wave which travels along the surface of the earth starting at the epicenter • Travels like ripples in a pond and can cause significant damage

  14. How are earthquakes classified? Mercalli Scale • Rated by intensity or damage 1 to 12 • Based on what you would feel in one area so one EQ can have many intensities • 1 detected only by seismographs and 12 is total destruction Richter Scale • Rated 1 to 10 • Measures EQ magnitude or power so each EQ has only one value. • Largest EQ ever recorded was an 9.5 on the Richter Scale (Chile 1960)

  15. 3-15-12 Aim: How do we measure an earthquake? • Do Now: • Which scale measures earthquake power? • Where do P, S, and L waves originate? • Where on the surface will the most shaking be experienced during an earthquake and why? HW: Finish lab.

  16. SeismographMachine used to measure seismic waves

  17. SeismogramReading from seismograph

  18. Practice • Figure out the difference between the P and S wave arrival times on the board for each seismogram. • If the difference in P and S wave arrival times increases with distance from the epicenter, then which seismogram came from the seismograph station closest to the earthquake?

  19. How to use the seismogram to find an earthquake epicenter • 1. Determine the difference in arrival time from the P wave and the S wave. • 2. Use the ESRT p.11to determine the epicenter distance and the P wave travel time. • 3. Subtract the P wave travel time from the P wave arrival time to determine the earthquake origin time. • 4. Draw a circle around the city with your epicenter distance as the radius. • 5. Do this for 3 seismic stations to pin point the location of the epicenter.

  20. Practice Problems • How long does it take for: • an S wave to travel 7,000 kilometers (km) • a P wave to travel 2,600 km • If the P wave arrives 5 minutes and 20 seconds after the earthquake actually occurs, how far away from the epicenter are you? When will the S wave arrive? • What is the difference in arrival time between the P and S waves if you are 4,400 km away from the epicenter. • a. What is the distance to the epicenter if the P and S wave arrive 3 minutes and 20 seconds apart. b. How long did it take the P wave to get there? c. If the P wave arrived at 2: 45 pm when did the earthquake occur

  21. Locating Epicenters-Triangulation • One seismic station can give us the distance only. • Two seismic stations can give us distance and 2 possible locations. • Three seismic stations can pinpoint an exact location for an epicenter.

  22. 3-19-12Aim: How can we use the Mercalli Scale to find an earthquake epicenter? • Do Now • 1. What information can be determined about an earthquake from a single seismic station? • 2. As distance from the epicenter increases what happens to difference in arrival times of P & S waves? • 3. How many seismic stations are needed to confirm an epicenter location? • 4. What is the Mercalli scale? • HW: R&H pp.246-252, A&E #9 – 28.

  23. 3-20-12Aim: What does a model of the earth’s interior look like? Do Now • How can earthquake magnitude be measured? • What special earth science day is it? Tell me all you know about it. • If we cannot physically drill to the center of the earth, how can we know what it looks like? HW: R&H 255-258 A&E 29-41

  24. Volcanoes Composite Cinder Cone

  25. Emergency Planning • Earthquakes cannot be predicted • If you ever find yourself in an earthquake “drop, cover, and hold” under a strong object or in a doorway. • Proper building codes are required in areas prone to EQ’s such as type of rock underneath the building and materials used to construct the building • Always have a disaster plan • Volcanoes can be predicted by measuring the small earthquakes leading up to an eruption and the swelling of the ground. • Always have a disaster plan • Tsunami warnings may offer a few hours notice. • Get to higher ground and find a secure structure. • The water recedes significantly before the waves start approaching. • Always have a disaster plan

  26. A Model of the Earth’s Interior • Properties of the earth’s interior were inferred by studying seismic waves • A wave’s speed will increase if the pressure or the density of the material it travels through are increasing • As the density of a material changes in each layer the wave is bent or refracted. • S- waves cannot travel through the liquid outer core and shadow zones where no waves are receceived are created. • We know the inner core is made of iron and nickel from studying meteorites that have hit the earth.

  27. The Moho is a boundry between the crust and the mantle at which waves refract. • The asthenosphere or the plastic mantle is the solid part of the mantle with the ability to flow (has plasticity), this is where convection causes the plates to move. • As depth increases in the earth, so does pressure, density, and temperature.

  28. Plate Tectonics 3/22/12 • Aim: What are the three types of plate boundaries and how have they formed the world we see today? • Do Now: 1. Using the diagram below please label the following; disturbed or undisturbed, oldest rock layer, foot wall, hanging wall, the stress (tension, compression, or shearing), type of fault, property of the rocks (brittle or ductile) • Explain how you could find a marine fossil on a mountain top or a shallow water fossil at great ocean depths. • How do we know the inner core is made of iron and nickel?

  29. Continental Drift • http://www.youtube.com/watch?v=hSdlQ8x7cuk • Continental Drift – thetheory that the continents were all once together and are slowly drifting apart. • Plate Tectonics – Earth’s lithosphere is broken up into plates which are constantly moving. (driven by convection cells in the mantle)

  30. Diverging Boundaries-plates are pulling apart. • Seafloor spreading creates new ocean crust at mid ocean ridges. Crust is youngest here.

  31. Converging Boundaries-plates are pushing together. Island Arcs, mountain ranges and ocean trenches can be formed. Continental crust which is always thicker and less dense will uplift and thinner, denser oceanic crust will always subside (go down) or subduct (slide beneath another plate)

  32. Transform Boundaries-plates are sliding horizontally past one another like the San Andreas Fault in CA. • Shearing tension builds up in the crust and is released periodically causing transform falult earthquakes

  33. 3/23/12 Aim: What evidence do we have for continental drift? • Do Now: • Name each of the three plate boundaries, the kind of stress which forms them, and the geological features seen at each one HW:R&H pp.259-267, A&E #42-68.

  34. Island Arcs vs. Island Chains • Island Arcs • Occur along Convergent plate boundaries • Formed by rising magma from melted subducting plate. • Ex. The Aleutian Islands • Island Chains • Occur over Hot Spots in the Earth’s mantle. • Formation of the Hawaiian Islands

  35. Four Pieces of Evidence That Support Continental Drift and Plate Tectonics 1. Puzzle Like Fit of the Continents 2. Matching Fossils on Different Continents 4. Glacial Deposits 3. Matching Rock Formations

  36. Magnetic Reversal • In a diverging oceanic plate boundary cooling rocks orient themselves to magnetic north. • Over time, about every100,000 years, magnetic north has switched from the geographic north pole to the geographic south pole and back again. • Geologists can match these orientations on either side of the plate boundary to show evidence of Seafloor Spreading. • Youngest rocks are found at the ridge and as distance from the ridge increases, age of the rock increases.

  37. Date: 3/30/11 Aim: What causes a tsunami? Do Now: • What is a tsunami? • Take out your laptops • Go to the class website • Look for the new page titled “Tsunami Detectives” HW: Fill in your “Tsunami Detective” Worksheet for the recent tsunami in Japan Study for Friday’s Test: Topic 12

  38. Learning Objectives • What causes a tsunami? • How are tsunamis related to the earthquakes we studied yesterday and how are they related to the concept of a dynamic crust?

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