Chapter 5 - Chapter 5 Earthquakes CHAPTER 5 EARTHQUAKES We...

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Chapter 5 Earthquakes 1 C HAPTER 5: E ARTHQUAKES We learn geology the morning after the earthquake, on ghastly diagrams of cloven mountains, up- heaved plains, and the dry bed of the sea. By Ralph Waldo Emerson, U.S. author
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Chapter 5 Earthquakes 2 C HAPTER 5.3 FAULTS , EARTHQUAKES , AND PLATES TECTON ICS pg. 117 KEY POINTS: Earthquakes begin at the focus, a point directly below the surface location of the earthquake (epicenter). Faults are classified by the relative direction of movement on either side of the fault. Faults usually do not move along their entire length; rather, they break along segments, with displacement along the fault rarely exceeding 5 meters. Earthquakes occur most frequently along plate boundaries, and the largest and deepest earthquakes are both associated with convergent plate boundaries. In the United States, Alaska has the largest earthquakes, but California experiences the greatest economic losses from earthquakes. Faults are zones of weakness – similar to the cracks in a sidewalk or the foundation of the house – where earthquakes can occur. They are found anywhere in a tectonic plate where sections of lithosphere can move relative to one another. A majority of earthquakes occur on faults that are located along plate boundaries. COMMON FEATURES OF FAULTS AND EARTHQUAKES: When describing earthquakes, geologists have identified several common feature. The location on the faults where movement begins (the earthquakes source) is called the focus (plural: foci). Earthquakes foci can occur at a range of depths down to 700 kilometers (435 miles) below the surface. The epicenter is the geographic location of Earth’s surface directly above the earthquake forcus. It is the location of the epicenter that provides the earthquake’s name. FOR EXAMPLE: the 2001 earthquake near Seattle was named the Nisqually earthquake because it focus was located 53 kilometers below the mouth of the Nisqually River in western Washington. Geologist identify faults by observing features on the land that have been displaced or rock layers that appear to have moved relative to one aonther. A change in the elevation of the land surface across the fault creates a feature known as a fault scarp. The fault plane is the surface along which the slip or movement occur during an earthquake. DIRECTIONS OF FAULT MOVEMENT: Faults are classified according to the relative movements of rocks on either side of the fault plane. Some fault exhibit vertical movements, where on side of the fault moves up or down relative to the other. If the block above the fault moves down, it is a normal fault; if the block above the fault moves up; it is a reverse fault. Alternatively, strike – slip faults exhibit horizontal movements, where one side of the faults move left (or
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Chapter 5 - Chapter 5 Earthquakes CHAPTER 5 EARTHQUAKES We...

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