Earthquakes revised

EARTHQUAKEARTHQUAKESES

http://video.nationalgeographic.com/video/environment/environment-natural-disasters/earthquakes/inside-earthquake/

FaultsFaultsFaultFault – a fracture or break – a fracture or break in the Earth’s lithospherein the Earth’s lithosphere

Rock along one side of a Rock along one side of a fault can move up, down, fault can move up, down, or sideways in relation to or sideways in relation to rock along the other side rock along the other side of the fault.of the fault.

How faults formHow faults form Forces cause rocks to bend & Forces cause rocks to bend &

stretch stretch Stress is the force exerted when a Stress is the force exerted when a

rock presses on, pulls on, or rock presses on, pulls on, or pushes against another rockpushes against another rock

As stress increases, the rocks As stress increases, the rocks may break.may break.

The break in the rock causes The break in the rock causes faults to form. faults to form.

EarthquakesEarthquakesEarthquakeEarthquake – the – the vibrations or sudden vibrations or sudden movements produced by movements produced by the breaking of rock.the breaking of rock.

Most earthquakes result Most earthquakes result from rocks moving over, from rocks moving over, under, or past each other under, or past each other along fault surfaces.along fault surfaces.

EarthquakesEarthquakesHow do earthquakes How do earthquakes actually occur?actually occur?

As rocks (plates) move As rocks (plates) move past each other along a past each other along a fault, their rough surfaces fault, their rough surfaces catch, temporarily catch, temporarily stopping movement.stopping movement.

EarthquakesEarthquakes Forces keep driving the rocks to Forces keep driving the rocks to

move, and stress builds up.move, and stress builds up. The stress causes the rocks to The stress causes the rocks to

bend and change shape, eventually bend and change shape, eventually breaking and causing an breaking and causing an earthquake.earthquake.

The strength of an earthquake The strength of an earthquake depends on: the amount of depends on: the amount of stress that builds & the stress that builds & the distance the rocks move along distance the rocks move along the faultthe fault

2005 Earthquakes2005 Earthquakes

Types of FaultsTypes of Faults Three types of forces –normal, Three types of forces –normal,

reverse, & strike-slip faultsreverse, & strike-slip faults Normal – pulls rocks apartNormal – pulls rocks apart Reverse – squeezes rocks Reverse – squeezes rocks

togethertogether Strike-slip – causes rocks to Strike-slip – causes rocks to

slide past each otherslide past each other

Normal FaultsNormal FaultsA break in rock caused A break in rock caused by by tension forcestension forces..

Rock above the fault Rock above the fault surface moves surface moves downwarddownward in relation to rock below in relation to rock below the fault surface.the fault surface.

Normal FaultNormal Fault

Reverse FaultsReverse FaultsA break in the rock A break in the rock caused by caused by compression compression forces. forces.

The rock above the fault The rock above the fault plane moves plane moves upwardupward relative to the rock relative to the rock below the fault surface. below the fault surface.

Reverse FaultReverse Fault

Reverse FaultReverse Fault

Strike-Slip FaultsStrike-Slip FaultsShearShear forces push on rock forces push on rock in in oppositeopposite directions. directions.

Rocks on either side of the Rocks on either side of the fault move fault move past each otherpast each other (without much upward or (without much upward or downward movement).downward movement).

Ex. San Andreas FaultEx. San Andreas Fault

Strike-Slip FaultStrike-Slip Fault

Strike-Slip FaultStrike-Slip Fault

Energy from Earthquakes Travels through Earth

Waves carry Waves carry energyenergy!! !! The energy from an The energy from an earthquake travels as earthquake travels as seismic wavesseismic waves, which , which cause the vibrations cause the vibrations during an earthquake.during an earthquake.

Focus & Epicenter

The The focusfocus of an earthquake is the of an earthquake is the point underground where rocks point underground where rocks 11stst begin to move. begin to move.

The The epicenterepicenter is the point on is the point on Earth’s surface directly above the Earth’s surface directly above the focus. focus.

Primary Waves Primary Waves

P waves P waves FastestFastest seismic waves seismic waves 11stst to reach any location to reach any location after an earthquakeafter an earthquake

Can travel through Can travel through solids, liquids, and gasessolids, liquids, and gases

Secondary Waves Secondary Waves SS waves waves 22ndnd wave to arrive at any wave to arrive at any

locationlocation Travel at Travel at ½ the speed of P ½ the speed of P

waveswaves Can travel through Can travel through solidsolid

(rocks) but NOT through (rocks) but NOT through liquid liquid and gasesand gases

Surface Waves Surface Waves Move along Move along Earth’s surfaceEarth’s surface, ,

but NOT through its’ but NOT through its’ interiorinterior Causes the largest Causes the largest ground ground

movementsmovements & the most & the most damagedamage

They make the ground They make the ground roll up roll up & down & down OR OR shake from side to shake from side to sideside

Damage from Damage from Earthquakes Earthquakes

The The Richter scaleRichter scale measures an measures an earthquake’s magnitude based earthquake’s magnitude based on how fast the ground moves on how fast the ground moves at the seismic station. at the seismic station.

SeismographSeismograph – the instrument – the instrument that constantly records ground that constantly records ground movement . Used to measure movement . Used to measure magnitude of an earthquake.magnitude of an earthquake.

Tsunami Tsunami Tsunami – is a water wave triggered by an Tsunami – is a water wave triggered by an

earthquake, volcanic eruption, or earthquake, volcanic eruption, or landslide. landslide.

They are sometimes called tidal wavesThey are sometimes called tidal waves May not be a single wave, but can be May not be a single wave, but can be

several waves with different heights and several waves with different heights and can arrive hours apart. can arrive hours apart.

They move quickly and can travel They move quickly and can travel thousandths of kilometers without thousandths of kilometers without weakening. Speeds can reach 430 mi/hr.weakening. Speeds can reach 430 mi/hr.

http://nctr.pmel.noaa.gov/animate.html

Japan Tsunami 2011

Liquefaction Liquefaction Liquefaction – the process in which Liquefaction – the process in which

shaking of the ground causes soil to shaking of the ground causes soil to act like a liquid. act like a liquid.

For a short time the soil acts like For a short time the soil acts like thick soupthick soup

It only occurs in areas where the soil It only occurs in areas where the soil is made up of loose sand and silt and is made up of loose sand and silt and contains a large amount of water. contains a large amount of water.