Chapter 8. Vibration of Earth produced by the rapid release of energy Focus – Point within Earth where the shaking begins Epicenter – is the location.

Earthquakes and Earth’s InteriorEarthquakes and Earth’s Interior

Chapter 8Chapter 8

EarthquakesEarthquakes

• 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 & FocusEpicenter & Focus

FaultsFaults

Cause of EarthquakesCause 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 Elastic Rebound

Hypothesis

Hypothesis

EarthquakesEarthquakes

Foreschocks• Days or years before a

major earthquake• Small

Aftershocks• Follow a major earthquake• Weaker than the major

earthquake

Measuring EarthquakesMeasuring Earthquakes

• Seismographs– Instruments that record earthquake waves

• Seismograms– Paper/ data from the seismograph

SeismographSeismograph

SeismogramSeismogram

Earthquake WavesEarthquake Waves

Surface 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

Body Waves• 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 AnimationWave Animation

• Earthquake Waves

Locating an EarthquakeLocating 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

TriangulationTriangulation

Travel Time GraphTravel Time Graph

Earthquake ZonesEarthquake 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 ActivityWorld Seismic Activity

Measuring EarthquakesMeasuring Earthquakes

Intensity• Measure of the amt of

earthquake shaking at a given location

• Based on the amount of damage

Magnitude• Measure the size of seismic

waves of amount of energy released

• Rely on calculations using seismograms

Richter ScaleRichter 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 ScaleModified Mercalli Scale

• Measures damage• Information gathered by surveying people in

the area

Mercalli ScaleMercalli Scale

Moment MagnitudeMoment Magnitude

• Most widely used measurement for earthquake

• Estimates the energy released by an earthquake

Moment MagnitudeMoment Magnitude

Seismic VibrationsSeismic 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 EarthquakesPredicting Earthquakes

• Earthquakes CANNOT be predicted

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

Haiti January 2010Haiti January 2010

Chile February 2010Chile February 2010

Chile February 2010Chile February 2010

Northridge, CA January 1994Northridge, CA January 1994

LiquefactionLiquefaction

• 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

LiquefactionLiquefaction

• Liquefaction

LiquefactionLiquefaction

Caused most damage in San Francisco Earthquake

Sand BoilsSand Boils

• Loma Prieta

TsunamisTsunamis

• 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 2004Indonesia 2004

Japan Tsunami 2011Japan Tsunami 2011

Japan Tsunami 2011Japan Tsunami 2011

Tsunami Warning SystemTsunami Warning System

• Earthquakes register to the Tsunami Warning Center in Hawaii

• Check water heights and issue warnings

Tsunami Warning SystemsTsunami Warning Systems

Tsunami Warning BuoyTsunami Warning Buoy

Tsuanami Warning SignsTsuanami Warning Signs

Earth’s Layers Chemical Earth’s Layers Chemical CompositionComposition

• 3 major zones based on chemical composition– Crust– Mantle – Core

CrustCrust

• Thin rocky outer layer• Continental Crust– 8-75 km thick– Over 4 billion years old

• Oceanic Crust– 7 km thick– 180 million years old or less

MantleMantle

• Solid, rocky shell that extends to a depth of 2890 km

• 82% of Earth’s volume

CoreCore

• Sphere composed of iron and nickel

Layers Defined Physical PropertiesLayers 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 LayersDiscovering Earth’s Layers

• Earth’s layers were discovered by studying seismic waves