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Understanding Earthquakes: Causes, Zones, and Waves

Explore the science behind earthquakes and their impact on Earth's surface. Learn about tectonic plate boundaries, fault types, and the different seismic waves. Discover where earthquakes occur and gain insight into their causes.

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Understanding Earthquakes: Causes, Zones, and Waves

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  1. Section 1What Are Earthquakes? Chapter F5 Do Now What do you think an earthquake is? Do you think the way earthquakes are portrayed on television and in movies is accurate? Why or why not? Write your answers in your science journal.

  2. Do Now • What are mountains? • What are the three main types of mountains? • Where are most mountains located?

  3. Section 1What Are Earthquakes? Chapter F5 Do Now What do you think an earthquake is? Do you think the way earthquakes are portrayed on television and in movies is accurate? Why or why not? Write your answers in your science journal.

  4. Objectives • Describe an earthquake and its relationship to shaping the surface of Earth.

  5. Agenda • Today we will: Day 1 • Complete a do now. • Learn about new vocabulary. • Complete a lab. • Exit ticket

  6. Vocabulary • seismology • seismic wave • epicenter • focus

  7. Section1 What Are Earthquakes? Chapter F5 What Are Earthquakes? • There is more to earthquakes than just the shaking of the ground. An entire branch of Earth science, called seismology, is devoted to the study of earthquakes. • Earthquakes are complex, and they present many questions for seismologists, the scientists who study earthquakes.

  8. Section1 What Are Earthquakes? Chapter F5 Where Do Earthquakes Occur? • Most earthquakes take place near the edges of tectonic plates. This figure shows the Earth’s tectonic plates and the locations of recent major earthquakes.

  9. Section1 What Are Earthquakes? Chapter F5 Where Do Earthquakes Occur?, continued • Tectonic plates move in different directions and at different speeds. As a result, numerous features called faults exist in the Earth’s crust. • A fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another. • Earthquakes occur along faults because of this sliding.

  10. Section1 What Are Earthquakes? Chapter F5 What Causes Earthquakes? • As tectonic plates move, stress increases along faults near the plates’ edges. In response to this stress, rock in the plates deforms. • Deformation is the change in the shape of rock in response to the stress of bending, tilting, and breaking of the Earth’s crust.

  11. Section1 What Are Earthquakes? Chapter F5 What Causes Earthquakes?, continued • Rock along a fault deforms in mainly two ways. • Rock deforms in a plastic manner, like a piece of molded clay, or in an elastic manner, like a rubber band. • Plastic deformation does not lead to earthquakes. Elastic deformation does. Like a rubber band, rock can be stretched only so far before it breaks.

  12. Section1 What Are Earthquakes? Chapter F5 What Causes Earthquakes?, continued • Elastic rebound is the sudden return of elastically deformed rock to its undeformed shape. Elastic rebound occurs when more stress is applied to rock than the rock can withstand. • During elastic rebound, energy is released. Some of this energy travels as seismic waves, which cause an earthquake.

  13. Section1 What Are Earthquakes? Chapter F5 Elastic Deformation and Elastic Rebound Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

  14. Section1 What Are Earthquakes? Chapter F5 Faults at Tectonic Plate Boundaries • A specific type of plate motion takes place at different tectonic plate boundaries. • Each type of motion creates a particular kind of fault that can produce earthquakes.

  15. Section1 What Are Earthquakes? Chapter F5 Faults at Tectonic Plate Boundaries, continued • Transform motion occurs where two plates slip past each other, creating strike-slip faults. Blocks of crust slide horizontally past each other.

  16. Section1 What Are Earthquakes? Chapter F5 Faults at Tectonic Plate Boundaries, continued • Convergent motion occurs where two plates push together, creating reverse faults. Blocks of crust that are pushed together slide along reverse faults.

  17. Section1 What Are Earthquakes? Chapter F5 Faults at Tectonic Plate Boundaries, continued • Divergent motion occurs where two plates pull away from each other, creating normal faults. Blocks of crust that are pulled away from each other slide along normal faults.

  18. Section1 What Are Earthquakes? Chapter F5 Faults at Tectonic Plate Boundaries, continued • Earthquake ZonesMost earthquakes happen in the earthquake zones along tectonic plate boundaries. Earthquake zones are places where a large number of faults are located. • Not all faults are located at tectonic plate boundaries. Sometimes, earthquakes happen along faults in the middle of tectonic plates.

  19. Section1 What Are Earthquakes? Chapter F5 How Do Earthquake Waves Travel? • Waves of energy that travel through the Earth away from an earthquake are called seismic waves. • Seismic waves that travel along the Earth’s surface are called surface waves.

  20. Section1 What Are Earthquakes? Chapter F5 Seismic Waves: Surface Waves Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

  21. Section1 What Are Earthquakes? Chapter F5 How Do Earthquake Waves Travel?, continued • Seismic waves that travel through Earth’s interior are called body waves. There are two types of body waves: P waves and S waves. • P waves are seismic waves that cause particles of rock to move in a back-and-forth direction. • S waves are seismic waves that cause particles of rock to move in a side-to-side direction.

  22. Section1 What Are Earthquakes? Chapter F5

  23. Section2 Earthquake Measurement Chapter F5 Locating Earthquakes • Scientists use seismographs to study earthquakes. • A seismograph is an instrument that records vibrations in the ground and determines the location and strength of an earthquake. • When earthquake waves reach a seismograph, it creates a seismogram, a tracing of the earthquake’s motion.

  24. Section2 Earthquake Measurement Chapter F5 Locating Earthquakes, continued • Determining Time and Location of Earthquakes Seismograms are used to find an earthquake’s epicenter. • An epicenter is the point on the Earth’s surface directly above an earthquake’s starting point.

  25. Section2 Earthquake Measurement Chapter F5 Locating Earthquakes, continued • A focus is the point inside the Earth where an earthquake begins. • An earthquake’s epicenter is on the Earth’s surface directly above the earthquake’s focus.

  26. Section2 Earthquake Measurement Chapter F5 Locating Earthquakes, continued • The S-P Time Method is perhaps the simplest method by which seismologists find an earthquake’s epicenter. • This method is explained in the following Visual Concepts presentation.

  27. Section2 Earthquake Measurement Chapter F5 S and P Time Method: Finding an Epicenter Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

  28. Section2 Earthquake Measurement Chapter F5 Measuring Earthquake Strength and Intensity • The Richter Magnitude Scale Throughout much of the 20th century, seismologists used a scale created by Charles Richter to measure the strength of earthquakes. • Earthquake Ground Motion A measure of the strength of an earthquake is called magnitude. The Richter scale measures the ground motion from an earthquake and adjusts for distance to find its strength.

  29. Section2 Earthquake Measurement Chapter F5 Richter Scale Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

  30. Section2 Earthquake Measurement Chapter F5 Measuring Earthquake Strength, continued • Modified Mercalli Intensity Scale A measure of the degree to which an earthquake is felt by people and the damage it caused is called intensity. • Currently, seismologists use the Modified Mercalli Intensity Scale to measure earthquake intensity. This is a numerical scale that uses Roman numerals from I to XII to describe earthquake intensity levels.

  31. Section2 Earthquake Measurement Chapter F5 Measuring Earthquake Strength, continued • In the Modified Mercalli Intensity Scale, an intensity of I describes an earthquake that is not felt by most people. An intensity level of XII indicates total damage of an area. • Because the effects of an earthquake vary based on location, any earthquake will have more than one intensity value. Intensity values usually are higher near the epicenter.

  32. Homework • Handouts

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