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Earthquakes - PowerPoint PPT Presentation

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  1. Earthquakes Sudden shaking and vibration of the ground caused by movement of the earth along a fault

  2. Earthquakes occur due to the elastic rebound theory

  3. When movement is initiated along a fault seismic waves radiate outward from the focus • Which are recorded using seismographs

  4. There are three types of seismic waves • P waves – Called primary waves, these are the fastest traveling waves • S waves – Called secondary waves arrive next, and can not travel through liquid • Surface waves – Are the slowest of the three and only travel along the surface

  5. P waves are analogous to sound waves in air (except P waves are 14 times faster), they are compressional waves • S waves are types of shear waves • Surface waves are similar to water waves

  6. An earthquake epicenter is located using the time interval between the arrival of the fist P and S wave • The time interval between them depends on how far they have traveled from the focus. The longer the time interval the further they have traveled • Readings from three seismograph stations are required to pinpoint the epicenter

  7. The size of an earthquakes is measured by assigning a Richter magnitude, which depends on the amplitude of ground movement

  8. Earthquakes are highly destructive and are often responsible for loss of life

  9. When an earthquake occurs offshore, a tsunami may be generated. These travel ~800 km/hr and can be higher than 20 meters when they hit land

  10. Earthquakes can not be accurately predicted by humans • To mitigate damage should enforce building codes and encourage public education