1. Rocks Move along Faults An earthquake is a shaking of the ground caused by the sudden movement of large blocks of rock along a fault. Earthquakes occur.

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Rocks Move along FaultsRocks Move along Faults

An An earthquakeearthquake is a shaking of the ground is a shaking of the ground caused by the sudden movement of large caused by the sudden movement of large blocks of rock along a fault. Earthquakes blocks of rock along a fault. Earthquakes occur along faults.occur along faults.

A A faultfault is a fracture, or break, in Earth’s is a fracture, or break, in Earth’s lithosphere, along which blocks of rock lithosphere, along which blocks of rock move past each other.move past each other.

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EarthquakesEarthquakes A sudden release of stress in the lithosphere A sudden release of stress in the lithosphere

causes an earthquake.causes 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 every More than 1,000,000 occur a year or one every

30 seconds30 seconds Earthquakes continue until all the energy is Earthquakes continue until all the energy is

used upused up TSUNAMIS- Earthquakes on the ocean floor: TSUNAMIS- Earthquakes on the ocean floor:

causing waves to become greater than 20 causing waves to become greater than 20 meters highmeters high

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Occurrence of EarthquakesOccurrence of Earthquakes

About 80 percent of all earthquakes occur About 80 percent of all earthquakes occur in a belt around the edges of the Pacific in a belt around the edges of the Pacific Ocean. Ocean.

In the United States, the best-known faultIn the United States, the best-known fault

in this belt is the San Andreas Fault in in this belt is the San Andreas Fault in California.California.

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San Andreas San Andreas Fault – This is a Transform Boundary that Fault – This is a Transform Boundary that runs from the Gulf of California through the San Francisco runs from the Gulf of California through the San Francisco area.area.

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Kinds of FaultsKinds of Faults

The three main types of faults are The 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 of Here the block of rock above the fault rock above the fault plane slides down plane slides down relative to the other relative to the other block. Stress that block. Stress that pulls rocks apart pulls rocks apart causes normal causes normal faults. Example - faults. Example - Great Rift Valley of Great Rift Valley of Africa.Africa.

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Reverse FaultsReverse FaultsHere the block of rock Here the block of rock above the fault plane above the fault plane moves up relative to moves up relative to the other block. Stress the other block. Stress that presses rocks that presses rocks together causes together causes reverse faults. These reverse faults. These faults can occur near faults can occur near collision-zone collision-zone boundaries between boundaries between plates. Example - plates. Example - Himalayan Mountains Himalayan Mountains have many have many earthquakes along earthquakes along reverse faults.reverse faults.

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Strike-Slip FaultsStrike-Slip FaultsHere blocks of rock move Here blocks of rock move sideways on either side of sideways on either side of the fault plane. Stress that the fault plane. Stress that pushes blocks of rock pushes blocks of rock horizontally causes horizontally causes earthquakes along strike-earthquakes along strike-slip faults. These faults can slip faults. These faults can occur where plates scrape occur where plates scrape past each other. The San past each other. The San Andreas Fault is a strike-Andreas Fault is a strike-slip fault.slip fault.

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Seismic WavesSeismic Waves

Energy from earthquakes travels through Energy from earthquakes travels through Earth. The energy travels as Earth. The energy travels as seismic seismic waveswaves which are vibrations caused by which are vibrations caused by earthquakes. Seismic waves from even earthquakes. Seismic waves from even small earthquakes can be recorded by small earthquakes can be recorded by sensitive instruments around the world.sensitive instruments around the world.

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Focus and EpicenterFocus and EpicenterAll earthquakes start All earthquakes start beneath Earth’s beneath Earth’s surface. The focus of surface. The focus of an earthquake is the an earthquake is the point underground point underground where rocks first begin where rocks first begin to move. Seismic to move. Seismic waves travel outward waves travel outward from the earthquake’s from the earthquake’s focus. The epicenter is focus. The epicenter is the point on Earth’s the point on Earth’s surface directly above surface directly above the focus.the focus.

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Seismic WavesSeismic Waves

Earthquakes produce three types of seismic Earthquakes produce three types of seismic waves: primary waves, secondary waves, and waves: primary waves, secondary waves, and surface waves. Each type moves through surface waves. Each type moves through materials differently. In addition, the waves can materials differently. In addition, the waves can reflect, or bounce, off boundaries between reflect, or bounce, off boundaries between different layers. The waves can also bend as different layers. The waves can also bend as they pass from one layer into another. Scientists they pass from one layer into another. Scientists learn about Earth’s layers by studying the paths learn about Earth’s layers by studying the paths and speeds of seismic waves traveling through and speeds of seismic waves traveling through Earth.Earth.

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Primary or P WavesPrimary or P Waves

Primary waves are Primary waves are the fastest(5 km or the fastest(5 km or 3mi/sec) and arrive 3mi/sec) and arrive first at the epicenterfirst at the epicenter

Can travel through Can travel through solids, liquids, and solids, liquids, and gasesgases

They are push-pull They are push-pull waveswaves

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Secondary or S WavesSecondary or S Waves

the second seismic waves the second seismic waves to arrive at any particular to arrive at any particular location after an location after an earthquake,earthquake,

travel through Earth’s travel through Earth’s interior at about half the interior at about half the speed of primary waves.speed of primary waves.

Can travel through solids, Can travel through solids, but but NOT NOT through liquids through liquids and gasesand 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 to make the ground roll up and down or shake from side to

side.side. 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 most cause the largest ground movements and the most

damage as they bend and twist the surfacedamage as they bend and twist the surface

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SeismometerSeismometer-an instrument -an instrument that constantly records ground that constantly records ground movementsmovements

SeismographSeismograph- Paper record of - Paper record of waves also used to determine waves also used to determine an earthquakes magnitude or an earthquakes magnitude or strength.strength.

SeismologistsSeismologists- scientists who - scientists who study earthquakesstudy earthquakes

Richter Scale-Richter Scale- a scale that a scale that allows scientists to determine allows scientists to determine earthquake strength based on earthquake strength based on many readings. 1-10 are levels many readings. 1-10 are levels at which an earthquake is at which an earthquake is measured based on amount of measured based on amount of damage caused; Levels above 7 damage caused; Levels above 7 are destructive. Each increasing are destructive. Each increasing number has 32 times more number has 32 times more energy.energy.

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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, Can cause fires (broken natural-gas lines,

electrical power lines, or overturned electrical power lines, or overturned stoves.)stoves.)

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AftershocksAftershocks

An aftershock is a smaller earthquakeAn aftershock is a smaller earthquake

that follows a more powerful earthquake in that follows a more powerful earthquake in the same area. Sometimes structures the same area. Sometimes structures weakened by an earthquake collapse weakened by an earthquake collapse during shaking caused by aftershocks.during shaking caused by aftershocks.

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LiquefactionLiquefaction

Earthquakes can cause soil liquefaction, a Earthquakes can cause soil liquefaction, a process in which shaking of the ground causes process in which shaking of the ground causes soil to act like a liquid. For a short time the soil soil to act like a liquid. For a short time the soil becomes like a thick soup. Liquefaction occurs becomes like a thick soup. Liquefaction occurs only in areas where the soil is made up of looseonly in areas where the soil is made up of loose

sand and silt and contains a large amount of sand and silt and contains a large amount of water. As the shaking temporarily changes the water. As the shaking temporarily changes the wet soil, structures either sink down into the soil wet soil, structures either sink down into the soil or flow away with it.or flow away with it.

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TsunamisTsunamis

A special type of wave, can make water rise A special type of wave, can make water rise more than the height of a 20-story building. more than the height of a 20-story building. This wave, known as a tsunami, is a water This wave, known as a tsunami, is a water wave triggered by an earthquake, volcanic wave triggered by an earthquake, volcanic eruption, or landslide. Tsunamis are eruption, or landslide. Tsunamis are sometimes called tidal waves.sometimes called tidal waves.

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The EndThe End

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