Earthquakes and Earth’s Interior Chapter 8

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

Epicenter & Focus

Faults

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

Elastic Rebound Hypothesis

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

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

Seismograph

Seismogram

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

Wave Animation Earthquake Waves

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

Triangulation

Travel Time Graph

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

World Seismic Activity

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

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

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

Mercalli Scale

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

Moment Magnitude

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

Predicting Earthquakes Earthquakes CANNOT be predicted

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

Haiti January 2010

Chile February 2010

Chile February 2010

Northridge, CA January 1994

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

Liquefaction Liquefaction

Liquefaction Caused most damage in San Francisco Earthquake

Sand Boils Loma Prieta

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)

Indonesia 2004

Japan Tsunami 2011

Japan Tsunami 2011

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

Tsunami Warning Systems

Tsunami Warning Buoy

Tsuanami Warning Signs

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

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

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

Core Sphere composed of iron and nickel

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)

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