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Chapter 2

Chapter 2. Earthquakes. Earthquakes Occur Along Faults. Chapter 2.1. Rocks Move Along faults. Fault: fracture or break in Earth’s lithosphere along which blocks of rock move past each other. Stress: Force exerted when an object pushes or pulls on another object.

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Chapter 2

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  1. Chapter 2 Earthquakes

  2. Earthquakes Occur Along Faults Chapter 2.1

  3. Rocks Move Along faults • Fault: fracture or break in Earth’s lithosphere along which blocks of rock move past each other. • Stress: Force exerted when an object pushes or pulls on another object. • Earthquake: shaking of the ground caused by the sudden movement of large blocks of rock along a fault

  4. Rocks move along Faults • Most faults are located at tectonic plate boundaries • 80% of all earthquakes occur in the belt around the pacific ocean. • San Andreas fault is best known fault in U.S.

  5. Faults are classified by how rocks move • Normal Faults: occur as rocks are pulled apart common in the Great Rift Valley of Africa

  6. Reverse Faults • Occur near collision-zone boundaries • Block of rock above the fault plane moves up relative to the other block.

  7. Slip Strike Fault • Blocks of rock move sideways on either side of the fault plane • Horizontal movement of rock

  8. Earthquakes Release Energy Chapter 2.2

  9. Energy from earthquakes travels through Earth • Seismic Waves: energy waves that travel as vibrations caused by earthquakes • Focus: point underground where rocks first begin to move, start of earthquake • Epicenter: point on Earth’s surface directly above the focus • Earthquakes are usually named for the city closest to the epicenter

  10. Energy from earthquakes travels through Earth

  11. Waves and Energy • What are some examples of waves in your world? • All waves including seismic waves carry energy from place to place

  12. Primary Waves • Fastest seismic waves • Also known as P-waves • Travel at 3mi/sec • Particles are pulled apart and pushed together in the direction the waves’ travel

  13. Secondary Waves • Second seismic waves to arrive at a location after an earthquake • Also known as S-waves • Half the speed of primary waves • Particles of materials move at right angle to the direction of the wave’s travel

  14. Surface Waves • Seismic waves that move along Earth’s surface • Slowest seismic wave • Cause the most damage

  15. Seismic Waves

  16. Seismic Waves

  17. Seismic Waves can be measured • Seismograph: instrument that constantly records ground movements.

  18. Using Seismographs • Record side-to-side and up-and-down movements. • Seismographs measure thousands of earthquakes around the world every year • By studying seismogram, scientists can determine the locations and strengths of earthquakes.

  19. Locating an Earthquake • Scientists find the difference between the arrival times of the p and s waves at each of three stations • The time difference is used to determine the distance of the epicenter from each station • A circle is drawn around each station with a radius corresponding to the epicenter’s distance from that station

  20. Locating an Earthquake

  21. Locating an Earthquake • Scientists use seismograph data to locate the focus of an earthquake • A seismogram can help determine an earthquakes magnitude (strength)

  22. Earthquake damage can be reduced Chapter 2.3

  23. Earthquakes can cause severe damage and loss of life • Every year on average an earthquake of magnitude 8 or higher strikes somewhere on Earth. • Most injuries and deaths are not caused by the movement of the ground but by collapsing buildings and fires.

  24. Earthquake magnitude • First scale developed by Charles Richter, the Richter scale. • Newer scale is called the moment magnitude scale • Each step up is an increase of 32 times the previous value.

  25. Earthquake magnitude

  26. Damage from earthquakes • Aftershock: smaller earthquake that follows a more powerful earthquake in the same area. • Liquefaction: a process in which shaking of the ground causes soil to act like a liquid. • Tsunami: water wave triggered by an earthquake, volcanic eruption or landslide. 2004 Sumatra tsunami killed nearly 300,000 people

  27. Scientists work to monitor and predict earthquakes

  28. Structures can be designed to resist earthquake damage • Best to be outdoors far from buildings during an earthquake • Use base isolators to insulate building from shock • Shear walls add strength to a building • Cross braces add structure

  29. Structures can be designed to resist earthquake damage

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