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Earthquakes Earthquakes are the vibrations vibrations caused by sudden movements of Earth’s rocks. Forces within the crust cause rocks to bend or break.

Earthquake Presentation 08 09

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Page 1: Earthquake Presentation 08 09

EarthquakesEarthquakesare the vibrationsvibrations caused by sudden

movements of Earth’s rocks.

Forces within the crust cause rocks to

bend or break.

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Where do most Earthquakes occur?

12%

88% Ring of Fire

All Others

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Most Earthquakes occur:

*along the “Ring of Fire”, a belt which circles the Pacific Ocean

*88% of all earthquakes occur here

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Earthquake Belts

along the belts which run through» central Asia» mid-ocean ridges» Mediterranean Sea» Caribbean Sea

Each black dot represents one earthquake over a 10 year period

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Earthquake Belts

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*due to one or a combination of more than one of three kinds of forces:

1. tension 2. compression 3. shearing

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Elastic Rebound

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ForcesForces may causerock to:

1. * Fracture » breaks in rock

where no movement has occurred

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ForcesForces may causerock to:

2. * Fault » fractures in rock where

movement has occurred» may occur in any direction

along the surface of the break (fault plane)

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*Fault Types

»may be one of three types:

1. normal

2. reverse

3. strike-slip (transform)

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Normal Fault

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Normal Fault

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Normal Fault

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Normal Fault Structures

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Reverse Fault

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Reverse Fault

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Reverse Fault

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Reverse Fault Structures

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Strike-slip (Transform) Fault

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Strike-slip (Transform) Fault

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Strike-Slip Fault

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Strike Slip Fault

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ForcesForces may cause rock to:

3. *Fold » due to compression» may form one single bend (monocline)» or may form alternating ridges (anticlines)

and troughs (synclines)

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monocline

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anticlines

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synclines

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Folded Rocks

anticline

syncline

Where are the oldest rocks exposed at the surface?

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Folded Rocks

monocline

rock has a gently dipping bend in the horizontal rock layer.

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Seismic Waves

originate from the *focus, the actual point on the fault where movement occurs

affect the point on the earth surface directly above the focus, called the *epicenter

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Seismic Waves

may be a *body wave:

1. *P- wave (primary) - rocks particles back and forth, fastest wave, first to arrive

2. *S - wave (secondary) - rocks move forward but vibrate at right angles to the direction of movement, slower than p - wave, arrives later

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Seismic Waves

may be a *surface wave:

3. *L- wave (longitudinal) - vibrates the earth’s crust like an ocean wave

is the most destructive

travels very slow compared to P & S – waves

last to reach the seismic station

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Seismic Waves

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Earthquake DestructionDestruction

Intensityis a measure of the physical damage or geologic change

measured by the

Mercalli Scale

Magnitudeis a measure of the strength of an earthquake recorded by seismographs

measured by the

Richter Scale

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How Seismographs Work

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Seismograph

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Richter Scale

For every increase in 1 on the Richter

Scale….

there is an increase of 32 times the

energy released!

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Seismogram

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P and S Wave Travel Time Curves

Use the difference in P and S wave arrival times to calculate the distance from the epicenter.

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Locating Earthquakes

Station 1Station 1

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Locating Earthquakes

Station 2

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Locating Earthquakes

Station 3

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Locating Earthquakes - Depth

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Seismic Waves in the Earth

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Seismic Waves in the Earth

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Earth’s Interior

P & S waves slow when they hit the upper mantle (asthenosphere)

speed up again when they hit the solid lower mantle

P waves are slowed and deflected when they hit the liquid outer core

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Earth’s Interior

S waves do not travel through the liquid outer core

Shadow Zone results between 105o and 140o from an earthquake’s focus

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Earth’s Interior

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Earth’s Interior

Why is the inner core a solid?

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Earth’s Interior

Crust: 3 – 60 miles thick, hard, brittle, continents are thicker than ocean

Mantle: thickest layer, denser than crust, upper mantle is plastic-like (flows under pressure)» Separated from the crust by the Moho or

Mohorovicic Discontinuity» Made of silicon, oxygen, magnesium, iron

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Earth’s Interior

Core: innermost layer, made of iron and nickel

» Inner core is solid

» Outer core is liquid

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Damage

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Earthquake Safety

Outdoors – move to an open area» Stay away from chimneys, buildings, trees» Stay away from beaches

Indoors » move away from windows, large objects» Seek shelter under table, desk, doorway, basement stairs» Turn off electricity, water, gas if possible

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Tsunamis

Probably Caused by Submarine Landslides

Travel about 400 m.p.h.

Pass Unnoticed at Sea, Cause Damage on Shore

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Tsunamis

Whether or Not Damage Occurs Depends on: » Direction of Travel » Harbor Shape » Bottom topography» Tide & Weather

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Tsunamis

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Satellite images from NASA show the destruction caused by a tsunami to the Indonesian province of Aceh. The left photo shows the town of Lhoknga before the tsunami hit on Dec. 24, 2004.

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Tsunamis

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Tsunamis

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Tsunamis