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Earthquakes and Earth’s Interior

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1 Earthquakes and Earth’s Interior
Chapter 8

2 Earthquakes Vibration of Earth produced by the rapid release of energy
Focus Point within Earth where the shaking begins Epicenter is the location on the surface directly above the focus Faults Fractures in Earth where movement has occurred

3 Epicenter & Focus

4 Faults

5 Cause of Earthquakes Rocks undergo stress and begin to bend storing up elastic energy Eventually the friction cannot keep the elastic energy in check and the rock snaps. Known as the Elastic Rebound Hypothesis

6 Elastic Rebound Hypothesis

7 Earthquakes Foreschocks Aftershocks
Days or years before a major earthquake Small Follow a major earthquake Weaker than the major earthquake

8 Measuring Earthquakes
Seismographs Instruments that record earthquake waves Seismograms Paper/ data from the seismograph

9 Seismograph

10 Seismogram

11 Earthquake Waves Surface Waves Body Waves
Move in up down and side to side motions Side to Side motion most damaging Most destructive earthquake waves Arrive at recording stations last P waves Push-pull waves Compression waves Quickest wave S waves Shake the particles at right angles to their direction of travel Called transverse waves Can not pass through gas or liquid

12 Wave Animation Earthquake Waves

13 Locating an Earthquake
Can be found using the differences between P and S wave speed The greater the difference in arrival time between P and S waves the farther from the epicenter Three seismograph stations are needed Called triangulation

14 Triangulation

15 Travel Time Graph

16 Earthquake Zones 95% of major earthquakes occur in a few narrow zones
Near the outer edge of the Pacific Ocean (Circum-Pacific belt) Japan, Philippines, Chile, Alaska Around the Mediterranean Sea (Mediterranean-Asian belt) Mid-Atlantic Ridge

17 World Seismic Activity

18 Measuring Earthquakes
Intensity Magnitude Measure of the amt of earthquake shaking at a given location Based on the amount of damage Measure the size of seismic waves of amount of energy released Rely on calculations using seismograms

19 Richter Scale Used on Television news reports not used by scientists
10 times stronger for every increase on the scale 5 earthquake is 10 times stronger than a 4

20 Modified Mercalli Scale
Measures damage Information gathered by surveying people in the area

21 Mercalli Scale

22 Moment Magnitude Most widely used measurement for earthquake
Estimates the energy released by an earthquake

23 Moment Magnitude

24 Seismic Vibrations Damage to buildings and other structures for earthquake waves depends on intensity and duration of vibrations and the material the structure is built on and the design of the structure

25 Predicting Earthquakes
Earthquakes CANNOT be predicted

26 Buildings Wood is better than concrete, bricks etc (more flexible)

27 Haiti January 2010

28 Chile February 2010

29 Chile February 2010

30 Northridge, CA January 1994

31 Liquefaction When loosely compacted sediments are saturated with water, stable soil behaves like a liquid When areas are backfilled causes problems Causes large amounts of damage to buildings

32 Liquefaction Liquefaction

33 Liquefaction Caused most damage in San Francisco Earthquake

34 Sand Boils Loma Prieta

35 Tsunamis Seismic sea waves
Triggered when a slab of the ocean floor is displaced along a fault Can occur when the vibration of a quake set an underwater landslide into motion (Indonesia 2006)

36 Indonesia 2004

37 Japan Tsunami 2011

38 Japan Tsunami 2011

39 Tsunami Warning System
Earthquakes register to the Tsunami Warning Center in Hawaii Check water heights and issue warnings

40 Tsunami Warning Systems

41 Tsunami Warning Buoy

42 Tsuanami Warning Signs

43 Earth’s Layers Chemical Composition
3 major zones based on chemical composition Crust Mantle Core

44 Crust Thin rocky outer layer Continental Crust Oceanic Crust
8-75 km thick Over 4 billion years old Oceanic Crust 7 km thick 180 million years old or less

45 Mantle Solid, rocky shell that extends to a depth of 2890 km
82% of Earth’s volume

46 Core Sphere composed of iron and nickel

47 Layers Defined Physical Properties
Lithosphere Outermost layer (100km thick) Crust and upper mantle Asthenosphere Lower mantle Weak layer Outer core Liquid layer Inner core Solid layer (due to pressure)

48 Discovering Earth’s Layers
Earth’s layers were discovered by studying seismic waves

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