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Earthquakes Booklet

Earthquakes Booklet. Forces in Earth’s Crust. stress -a force that acts on rock to change its shape or volume . 3 Types of Stress tension -pulls on crust, stretching rock so it becomes thinner in the middle compression -squeezes rock together until it folds or breaks

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Earthquakes Booklet

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  1. Earthquakes Booklet

  2. Forces in Earth’s Crust • stress -a force that acts on rock to change its shape or volume. 3 Types of Stress • tension -pulls on crust, stretching rock so it becomes thinner in the middle • compression -squeezes rock together until it folds or breaks • shearing-pushes rock in two opposite directions

  3. Fault I • Type of Fault: • Reverse Fault • Stress Force: • Compression • Movement Along Fault: • The hanging wall is moving up relative to the footwall

  4. Fault II • Type of Fault: • Normal Fault • Stress Force: • Tension • Movement Along Fault: • The hanging wall is moving down relative to the footwall

  5. Fault III • Type of Fault: • Strike-Slip Fault • Stress Force: • Shearing • Movement Along Fault: • Opposing forces cause the rock to break and move horizontally

  6. What Causes Earthquakes? • Deformation– the process by which the shape of a rock changes because of stress • Elastic Rebound – the sudden return of elastically deformed rock to its undeformed shape • What is the direct cause of earthquakes? • Elastic rebound

  7. “SEISMO” ….means “to shake” • Seismology – the study of earthquakes • Seismic Waves – a wave of energy that travels through the Earth, away from an earthquake in all directions • Seismograph – an instrument that records vibrations in the ground and determines the location and strength of an earthquake • Seismogram – a tracing of earthquake motion that is created by a seismograph • Seismic Gap – an area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes have occurred in the past And some other important terms… • Epicenter – the point on Earth’s surface directly above an earthquake’s starting point, or focus • Focus – the point along a fault at which the first motion of an earthquake occurs

  8. Earthquake Waves Body Waves • P waves (pressure or primary waves) arrive first, travel through liquid • S Waves (secondary waves) arrive later, can not travel through liquid

  9. Earthquake Waves

  10. Measuring Earthquakes • The S-P Time Method • Describe how a seismograph is used to determine the epicenter of an earthquake. • p 231

  11. Strength & Intensity • What does the Richter Scale measure? • The strength of earthquakes – measures the ground motion from an earthquake and adjusts for distance to find its strength • What is the magnitude of an earthquake? • The strength • How are magnitude and ground motion related in the Richter scale? • Each time the magnitude increases by 1 unit, the amount of ground motion increases by 10 times • What does the Modified Mercalli Intensity Scale measure? • The degree to which an earthquake is felt by people and the amount of damage caused b the earthquake • Why might an earthquake have more than one intensity value? • Because the effects of an earthquake vary from place to place, the intensity values are usually higher near the earthquakes epicenter

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