chapter_16_powerpt.CM-11e

chapter_16_powerpt.CM-11e - Earthquakes Physical Geology...

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Steve Kadel, Glendale Community College Earthquakes Physical Geology 11/e, Chapter 16
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Earthquakes This chapter will help you understand the nature and origin of earthquakes discuss the seismic waves created by earthquakes discuss how the quakes are measured and located by using seismic waves describe some effects of earthquakes such as ground motion and displacement, damage to buildings, quake caused fires, landslides, and seismic sea waves (tsunami)
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Fig. 16.1B. Collapsed double-deck Cypress freeway in Oakland after the 1989 Loma Prieta earthquake
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Fig. 16.1d Fig. 16.1D. The collapse of the lower story of the Northridge Meadow Apartments killed sixteen people in the 1994 earthquake in San Fernando Valley, southern California
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Fig. 16.1E. Damage from falling bricks in downtown Seattle after the February 28, 2001, Nisqually earthquake
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Earthquakes An earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath Earth’s surface Tectonic forces within the Earth produce stresses on rocks that eventually exceed their elastic limits, resulting in brittle failure Energy is released during earthquakes in the form of seismic waves Released from a position along a break between two rock masses (fault) Elastic rebound theory – explains the occurrence of earthquakes are a sudden release of strain progressively stored in rocks that bend until they finally break and move along a fault
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Fig. 16.2 The elastic rebound theory of the cause of earthquakes. Fig. 16.2D. Fence offset nearly 3 meters after 1906 San Francisco earthquake
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Elastic Rebound (From Tarbuck & Lutgens, 8e)
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Seismic Waves The point within the Earth where seismic waves originate is called the focus (or hypocenter ) of the earthquake, and is the point of initial breakage and movement along a fault The point on the Earth’s surface directly above the focus is known as the epicenter Two types of waves are produced during earthquakes: body waves and surface waves Body waves are seismic waves that travel outward from the focus in all directions through Earth’s interior Surface waves are seismic waves that travel along Earth’s surface away from the epicenter in all directions
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Fig. 16.4 The focus of an earthquake is the point where rocks first break along a fault; seismic waves radiate from the focus.
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Body Waves P waves are compressional (or longitudinal) body waves in which rock vibrates back and forth parallel to the direction of wave propagation Fast (4 to 7 kilometers per second) wave that is the first or primary wave to arrive at a recording station following an earthquake Can pass through solids and fluids (liquids or gases) S waves are shearing (or transverse) body waves in which rock vibrates back and forth perpendicular to the direction of wave propagation Slower (2 to 5 kilometers per second) wave that is the secondary wave to arrive at a recording station following an earthquake Slightly greater amplitude than P waves Can pass only through solids
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Fig. 16.5A. & B. Particle motion in seismic waves
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This note was uploaded on 06/13/2011 for the course GEOL 1403 taught by Professor Mulcahey during the Spring '11 term at Lone Star College System.

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chapter_16_powerpt.CM-11e - Earthquakes Physical Geology...

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