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EARTHQUAKES AND EARTH’S INTERIOR

EARTHQUAKES AND EARTH’S INTERIOR. Objectives. Explain the connection between earthquakes and plate tectonics. Identify several earthquake-related hazards. Define body waves and surface waves. Explain how the materials in Earth’s interior affect seismic waves.

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EARTHQUAKES AND EARTH’S INTERIOR

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  1. EARTHQUAKES AND EARTH’S INTERIOR

  2. Objectives Explain the connection between earthquakes and plate tectonics. Identify several earthquake-related hazards. Define body waves and surface waves. Explain how the materials in Earth’s interior affect seismic waves. Define and describe the composition of Earth’s crust, mantle and core.

  3. Megathrust earthquakes

  4. Earthquakes and earthquake hazards Seismology The scientific study of earthquakes and seismic waves Seismic waves An elastic shock wave that travels outward in all directions from an earthquake’s source Seismic creep

  5. Earthquakes and plate motion The elastic rebound theory Continuing stress along a fault Results in buildup of elastic energy in the rocks Energy abruptly released when an earthquake occurs

  6. Earthquakes and plate motion

  7. Earthquake Hazards and Predictions Primary hazards Collapsing buildings, bridges and other structures Aftershock Secondary hazards Landslides, fires, ground liquefaction, tsunamis

  8. Earthquake hazards Landslide, Huascaran, Peru Open fissure, Golcuk, Turkey

  9. Earthquake hazards Fire, San Francisco, California Ground liquification, Niigata, Japan

  10. The Sumatra-Andaman Tsunami (2004)

  11. Earthquake prediction Short-term prediction and early warning Precursor phenomena Foreshocks Long-term forecasting Paleoseismology The study of prehistoric earthquakes Seismic gaps

  12. Earthquake Readiness Preparation and readiness to earthquakes key to reducing fatalities Reinforced structures Bolting wood-framed buildings to foundation Protecting utility lines from movement Education

  13. The Science of Seismology Seismograph An instrument that detects and measures vibrations of Earth’s surface Advanced seismographs detect vibrations 10-8 of a centimeter Seismogram The record made by a seismograph

  14. The Science of Seismology

  15. Seismic waves Body wave Travels through Earth’s interior Surface wave Travels along Earth’s surface Focus Where rupture commences and an earthquake’s energy is first released

  16. Locating earthquakes Compressional wave: Wave consisting of alternating pulses of compression and expansion Can pass through any medium (solids, liquids, gases) P (or primary) wave Shear wave: Rock is subjected to side to side or up and down forces, perpendicular to wave’s direction of travel S (secondary) wave Not transmitted through water Travel slower than P waves

  17. Locating earthquakes

  18. Locating earthquakes

  19. Locating earthquakes Epicenter The point on Earth’s surface directly above an earthquake’s focus

  20. Locating earthquakes

  21. Measuring Earthquakes The Richter Magnitude Scale A scale of earthquake intensity based on the recorded heights, or amplitudes, of the seismic waves recorded on a seismograph A logarithmic scale—a 10 fold increase in amplitude for each unit Moment Magnitude Scale A measure of earthquake strength that is based on the rupture size, rock properties, and amount of displacement on the fault surface

  22. Measuring Earthquakes Richter magnitude 7 Richter magnitude 6 Richter magnitude 8

  23. Studying Earth’s Interior Seismic discontinuity A boundary inside Earth where the velocities of seismic waves change abruptly

  24. Studying Earth’s Interior

  25. Studying Earth’s Interior Three things can happen to seismic waves when they meet a boundary Refraction: bent as they pass from one material to another Reflection: some or all of the wave energy bounces back Absorption: some or all of the wave energy is blocked

  26. How geologists look into Earth’s interior Seismic tomography Allows geologists to image inside of Earth Direct observation Drilling Xenoliths Indirect observation Magnetism Density

  27. Diamonds!

  28. A Multilayered Planet Crust The outermost compositional layer of the solid Earth, part of the Lithosphere Thickness ranges between 8 kilometers (oceanic) and 45 km (continental)

  29. A Multilayered Planet

  30. A Multilayered Planet Mantle The middle compositional layer of Earth, between the core and the crust Comprised primarily of olivine and pyroxene Asthenosphere: mantle where rock is near melting Mantle-core boundary: mesosphere

  31. A Multilayered Planet

  32. Core Innermost layer, where the magnetic field is generated and much geothermal energy resides Separated into outer core (liquid) and inner core (solid) A Multilayered Planet

  33. Critical Thinking If you were on a ship in the ocean, would you be able to feel an earthquake that occurred below you, on the ocean floor? Do you think there is no limit to the magnitude of earthquakes? What kind of wave would you expect to travel faster: a seismic wave or a tsunami wave?

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