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Rocks Move along FaultsRocks Move along Faults
An earthquake is a shaking of the groundcaused by the sudden movement of largeblocks of rock along a fault. Earthquakesoccur along faults.An earthquake is a shaking of the groundcaused by the sudden movement of largeblocks of rock along a fault. Earthquakesoccur along faults.
A fault is a fracture, or break, in Earth’slithosphere, along which blocks of rockmove past each other. A fault is a fracture, or break, in Earth’slithosphere, along which blocks of rockmove past each other.
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EarthquakesEarthquakes
A sudden release of stress in the lithospherecauses an earthquake.A sudden release of stress in the lithospherecauses an earthquake.
Shaking and trembling of the earth’s crust.Shaking and trembling of the earth’s crust.
The waves travel in all directionsThe waves travel in all directions
More than 1,000,000 occur a year or one every30 secondsMore than 1,000,000 occur a year or one every30 seconds
Earthquakes continue until all the energy isused upEarthquakes continue until all the energy isused up
TSUNAMIS- Earthquakes on the ocean floor:causing waves to become greater than 20meters highTSUNAMIS- Earthquakes on the ocean floor:causing waves to become greater than 20meters high
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Occurrence of EarthquakesOccurrence of Earthquakes
About 80 percent of all earthquakes occurin a belt around the edges of the PacificOcean.About 80 percent of all earthquakes occurin a belt around the edges of the PacificOcean.
In the United States, the best-known faultIn the United States, the best-known fault
in this belt is the San Andreas Fault inCalifornia.in this belt is the San Andreas Fault inCalifornia.
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San Andreas Fault – This is a Transform Boundary thatruns from the Gulf of California through the San Franciscoarea.San Andreas Fault – This is a Transform Boundary thatruns from the Gulf of California through the San Franciscoarea.
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Kinds of FaultsKinds of Faults
The three main types of faults areThe three main types of faults are
1) Normal faults,1) Normal faults,
2) Reverse faults, and2) Reverse faults, and
3) Strike-slip faults.3) Strike-slip faults.
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Normal FaultsNormal Faults
Here the block ofrock above the faultplane slides downrelative to the otherblock. Stress thatpulls rocks apartcauses normalfaults. Example -Great Rift Valley ofAfrica.Here the block ofrock above the faultplane slides downrelative to the otherblock. Stress thatpulls rocks apartcauses normalfaults. Example -Great Rift Valley ofAfrica.
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Reverse FaultsReverse Faults
Here the block of rockabove the fault planemoves up relative tothe other block. Stressthat presses rockstogether causesreverse faults. Thesefaults can occur nearcollision-zoneboundaries betweenplates. Example -Himalayan Mountainshave manyearthquakes alongreverse faults.Here the block of rockabove the fault planemoves up relative tothe other block. Stressthat presses rockstogether causesreverse faults. Thesefaults can occur nearcollision-zoneboundaries betweenplates. Example -Himalayan Mountainshave manyearthquakes alongreverse faults.
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Strike-Slip FaultsStrike-Slip Faults
Here blocks of rock movesideways on either side ofthe fault plane. Stress thatpushes blocks of rockhorizontally causesearthquakes along strike-slip faults. These faults canoccur where plates scrapepast each other. The SanAndreas Fault is a strike-slip fault.Here blocks of rock movesideways on either side ofthe fault plane. Stress thatpushes blocks of rockhorizontally causesearthquakes along strike-slip faults. These faults canoccur where plates scrapepast each other. The SanAndreas Fault is a strike-slip fault.
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Seismic WavesSeismic Waves
Energy from earthquakes travels throughEarth. The energy travels as seismicwaves which are vibrations caused byearthquakes. Seismic waves from evensmall earthquakes can be recorded bysensitive instruments around the world.Energy from earthquakes travels throughEarth. The energy travels as seismicwaves which are vibrations caused byearthquakes. Seismic waves from evensmall earthquakes can be recorded bysensitive instruments around the world.
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Focus and EpicenterFocus and Epicenter
All earthquakes startbeneath Earth’ssurface. The focus of anearthquake is the pointunderground whererocks first begin tomove. Seismic wavestravel outward from theearthquake’s focus. Theepicenter is the point onEarth’s surface directlyabove the focus.All earthquakes startbeneath Earth’ssurface. The focus of anearthquake is the pointunderground whererocks first begin tomove. Seismic wavestravel outward from theearthquake’s focus. Theepicenter is the point onEarth’s surface directlyabove the focus.
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Seismic WavesSeismic Waves
Earthquakes produce three types of seismicwaves: primary waves, secondary waves, andsurface waves. Each type moves throughmaterials differently. In addition, the waves canreflect, or bounce, off boundaries betweendifferent layers. The waves can also bend asthey pass from one layer into another. Scientistslearn about Earth’s layers by studying the pathsand speeds of seismic waves traveling throughEarth.Earthquakes produce three types of seismicwaves: primary waves, secondary waves, andsurface waves. Each type moves throughmaterials differently. In addition, the waves canreflect, or bounce, off boundaries betweendifferent layers. The waves can also bend asthey pass from one layer into another. Scientistslearn about Earth’s layers by studying the pathsand speeds of seismic waves traveling throughEarth.
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Primary or P WavesPrimary or P Waves
Primary waves arethe fastest(5 km or3mi/sec) and arrivefirst at the epicenterPrimary waves arethe fastest(5 km or3mi/sec) and arrivefirst at the epicenter
Can travel throughsolids, liquids, andgasesCan travel throughsolids, liquids, andgases
They are push-pullwavesThey are push-pullwaves
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Secondary or S WavesSecondary or S Waves
the second seismic wavesto arrive at any particularlocation after anearthquake,the second seismic wavesto arrive at any particularlocation after anearthquake,
travel through Earth’sinterior at about half thespeed of primary waves.travel through Earth’sinterior at about half thespeed of primary waves.
Can travel through solids,but NOT through liquidsand gasesCan travel through solids,but NOT through liquidsand gases
Move in up-down motionMove in up-down motion
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Surface or L WavesSurface or L Waves
seismic waves that move along Earth’s surface, notseismic waves that move along Earth’s surface, not
through its interior.through its interior.
make the ground roll up and down or shake from side toside.make the ground roll up and down or shake from side toside.
Slowest moving seismic wavesSlowest moving seismic waves
Travel on top of Earth’s surfaceTravel on top of Earth’s surface
cause the largest ground movements and the mostdamage as they bend and twist the surfacecause the largest ground movements and the mostdamage as they bend and twist the surface
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Seismometer-an instrumentthat constantly records groundmovementsSeismometer-an instrumentthat constantly records groundmovements
Seismograph- Paper record ofwaves also used to determinean earthquakes magnitude orstrength.Seismograph- Paper record ofwaves also used to determinean earthquakes magnitude orstrength.
Seismologists- scientists whostudy earthquakesSeismologists- scientists whostudy earthquakes
Richter Scale- a scale thatallows scientists to determineearthquake strength based onmany readings. 1-10 are levelsat which an earthquake ismeasured based on amount ofdamage caused; Levels above 7are destructive. Each increasingnumber has 32 times moreenergy.Richter Scale- a scale thatallows scientists to determineearthquake strength based onmany readings. 1-10 are levelsat which an earthquake ismeasured based on amount ofdamage caused; Levels above 7are destructive. Each increasingnumber has 32 times moreenergy.
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Damage from EarthquakesDamage from Earthquakes
Loss of lifeLoss of life
Damage to buildingsDamage to buildings
Can cause fires (broken natural-gas lines,electrical power lines, or overturnedstoves.)Can cause fires (broken natural-gas lines,electrical power lines, or overturnedstoves.)
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AftershocksAftershocks
An aftershock is a smaller earthquakeAn aftershock is a smaller earthquake
that follows a more powerful earthquake inthe same area. Sometimes structuresweakened by an earthquake collapseduring shaking caused by aftershocks.that follows a more powerful earthquake inthe same area. Sometimes structuresweakened by an earthquake collapseduring shaking caused by aftershocks.
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LiquefactionLiquefaction
Earthquakes can cause soil liquefaction, aprocess in which shaking of the ground causessoil to act like a liquid. For a short time the soilbecomes like a thick soup. Liquefaction occursonly in areas where the soil is made up of looseEarthquakes can cause soil liquefaction, aprocess in which shaking of the ground causessoil to act like a liquid. For a short time the soilbecomes like a thick soup. Liquefaction occursonly in areas where the soil is made up of loose
sand and silt and contains a large amount ofwater. As the shaking temporarily changes thewet soil, structures either sink down into the soilor flow away with it.sand and silt and contains a large amount ofwater. As the shaking temporarily changes thewet soil, structures either sink down into the soilor flow away with it.
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TsunamisTsunamis
A special type of wave, can make water risemore than the height of a 20-story building.This wave, known as a tsunami, is a waterwave triggered by an earthquake, volcaniceruption, or landslide. Tsunamis aresometimes called tidal waves.A special type of wave, can make water risemore than the height of a 20-story building.This wave, known as a tsunami, is a waterwave triggered by an earthquake, volcaniceruption, or landslide. Tsunamis aresometimes called tidal waves.
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The EndThe End
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Ring of FireRing of Fire
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