Earthquakes. (1) What causes earthquakes? It’s plate movement Movement in the crust causes stress– energy that slowly changes the shape of rock Earthquake–

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(1) What causes earthquakes?It’s plate movement

Movement in the crust causes stress– energy that slowly changes the shape of rock

Earthquake– shaking from the sudden movement of rock at a fault (stress is quickly released)

Bedarliex, Bedarliex, FranceFrance

Fault energy can be released all at once and cause elastic rebound

(2) Where do earthquakes occur?

Pacific Plate N.A. Plate

(2) Where do earthquakes occur?1) At strike-slip faults, plates

move at sliding boundaries (San Andreas Fault, CA)

Pacific Plate N.A. Plate

(2) Where do earthquakes occur?1) At strike-slip faults, plates

move at sliding boundaries (San Andreas Fault, CA)

2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan)

N. A. Plate Pacific Plate

Where do earthquakes occur?1) At strike-slip faults, plates

move at sliding boundaries (San Andreas Fault, CA)

2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan or Chile)

3) Smaller ‘quakes happen at mid-ocean ridges & rift

zones, spreading boundaries

(Mid-Atlantic Ridge)

N. A. Plate

Eurasian Plate

Epicenter & Focus

epicenter- point on Earth’s surface directly above the focus

focus- area beneath the surface, where the release of fault energy starts an earthquake

(4) What are seismic waves?seismic waves- vibrations

made from the release of an earthquake’s energy

These waves travel outward from the focus…

(4) What are seismic waves?seismic waves- vibrations

made from the release of an earthquake’s energy

These waves travel outward from the focus…

…underground through Earth’s body of solid rock

(P waves or S waves)

(4) What are seismic waves?seismic waves- vibrations

made from the release of an earthquake’s energy

These waves travel outward from the focus…

…underground through Earth’s body of solid rock

(P waves or S waves)

…and above ground as destructive surface waves

(L waves, long-waves)

(5) How do waves move underground?First, there are…

P waves- Primary or - Primary or pressure waves are the pressure waves are the fastestfastest, and cause rock , and cause rock to compress & expand to compress & expand (push-pull)(push-pull)

(6) Next, are underground… S waves- secondary or

shear waves; travel slower than primary waves, up-and-down (back and forth)

(7) S waves can move through solids (rock), but NOT through

liquids or gases

What happens to the S waves (blue)?

(8) How do surface waves move?P and S waves above the

ground…

…are L waves, called surface waves- the slowest waves; slower than P & S waves

(8) How do surface waves move?P and S waves above the

ground…

…are L waves, called surface waves- the slowest waves; slower than P & S waves

…cause severe shearing of the ground (side-to-side)

…can make the ground roll like waves on water

http://blogs.agu.org/mountainbeltway/category/japan/

Penn. State Univ. Penn. State Univ. http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html

WikipediaWikipedia

Where do earthquakes occur?1) At strike-slip faults, plate

move at sliding boundaries (San Andreas Fault, CA)

2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan or Chile)

3) Smaller ‘quakes happen at mid-ocean ridges, spreading boundaries (Mid-Atlantic Ridge)

Nazca Plate S. A. Plate

How does a magnitude 6 compare to a 5 ?

The waves are 10 timesThe waves are 10 times greater from a magnitude 6 greater from a magnitude 6 than those from a magnitude 5 earthquakethan those from a magnitude 5 earthquake

A magnitude 6 releases about A magnitude 6 releases about 30 times30 times more energy more energy than a magnitude 5 than a magnitude 5

Richter Magnitude

Strength

(amplitude)

Energy Released

5 X Y

6 10X 30Y

7 100X 1000Y