Chapter 8. Vibration of Earth produced by the rapid release of energy Focus – Point within Earth...
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Transcript of Chapter 8. Vibration of Earth produced by the rapid release of energy Focus – Point within Earth...
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