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Earthquakes!!! Slide 1 How and Where Earthquakes Occur Earthquake- the shaking of the Earth’s crust caused by the release of energy Earthquakes can be caused by volcanic eruption, collapse of a caldera, or even the impact of a meteor. Most earthquakes occur along faults .( A fault is a break in the lithosphere along which movement has occurred) Slide 2 Friction Friction makes it difficult for the plates Tension/pressure builds until it the to move smoothly forces become too much and rapid movement occurs (earthquake) Following the earthquake, the plates may return to their original form and shape, but the damage is already done on the surface. This is called elastic rebound theory. Slide 3 Movement first occurs at the focus of the earthquake The focus is well below the surface The epicenter of the earthquake is the place on the surface of the Earth directly above the focus. Slide 4 The depth of an earthquake depends upon the type of plate boundary involved Energy waves that travel through the Earth are called body waves. Slide 5 P waves (primary waves) squeeze and stretch rock materials. P waves can travel though any material. S waves (secondary or shear waves) cause rock material to move at right angles to the direction the wave is traveling. S waves can travel through solids, but not through liquids and gases. Slide 6 Surface waves travel along the Earth’s surface and can produce Love and Rayleigh waves Slide 7 Locating and Measuring Earthquakes A seismograph detects and records waves produced by earthquakes A seismogram is a recording sheet that shows an earthquake in graphic form Slide 8 3 recording stations are needed to locate the epicenter of an earthquake ( We will do an activity to demonstrate this) Magnitude of an earthquake is a measure of the amount of energy released. The Richter scale is used to measure the energy of an earthquake. ( An increase in 1 number is a 31-fold increase in energy) Slide 9 A 7 earthquake has 31 times more energy than a 6 A 7 has 961 times more energy than a 5 (31 X 31) Slide 10 Earthquake Hazards Liquefaction occurs when loose soil temporarily takes on the properties of a liquid. Buildings located on this soil lose their support. Slide 11 Aftershocks often occur after the major earthquake There can be up to 1000 aftershocks per day. Underwater earthquakes and landslide can cause tsunamis. Tsunamis can travel up to 750 km/hr in deep water. Tsunami photo Slide 12 When earthquakes occur in populated areas, infrastructure (roads, bridges, water and gas pipes, communication cables ) often suffer damage. This can lead to fires which are difficult to put out.