Earthquakes Earth Science. What is an Earthquake? A vibration of the Earth produced by a rapid...
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Transcript of Earthquakes Earth Science. What is an Earthquake? A vibration of the Earth produced by a rapid...
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Earthquakes
Earth Science
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What is an Earthquake? A vibration of the Earth produced by a rapid energy
release The point within the earth where an earthquake starts is
called the focusEnergy travels from the focus in all directions- think of a
stone being tossed into a pondStone sets waves of motion in water just as seismic waves
move through earthThe point on the surface of the Earth above the focus is called
the epicenter
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The Epicenter The epicenter is the
location directly above the focus
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Earthquakes over a 10 yr. period Pacific Ring of fire
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Faults Faults are fractures in the Earth where plate
movement has occurred There are three types of forces that create faults.
Compression - squeezesTension - stretchesShear – causes slippage
Each of these three forces can create a different kind of fault.
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Earthquake causes Elastic Rebound hypothesis
Rock is bending causing elastic stressEventually the rock will slip and break at the weakest
point (the focus)The vibrations we feel occur as the rock returns to its
original shape
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Types of faults Normal Faults- caused by tension forces Reverse Faults- compression Strike-Slip Faults- shear forces
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Normal Faults Tension causes rocks to be
pulled apart. Rock above the fault surface
moves downward in relation to rock below the fault surface.
Can help to form mountains such as the Sierra Nevada Mountain Range
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Reverse Fault Compression causes rock
to break. Rocks above the fault
surface are forced up and over the rocks below the faults.
Can form mountains such as the Rockies.
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Strike-Slip Fault Two of Earth’s plates
move past each other due to shear forces.
There is very little vertical movement
Ex: San Andreas Fault
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Earthquake Info Seismic waves – waves
that move through the Earth’s crust
Seismic waves travel outward from the focus of an earthquake
Surface Waves- these travel along Earth’s outer layer
Body waves- travel through Earth’s interior Primary Waves (P) – waves
that travel in the same direction the wave is moving
Secondary Waves (S) – move through the Earth causing particles to move at right angles to the direction of the wave.
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Wave Facts Surface waves (S) are the slowest waves, primary (P Waves) are
the fastest. P Waves can only travel through solids. P waves travel 1.7 times faster than S waves
Surface waves cause the most destruction during an earthquake.
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Measuring Earthquakes Seismologists use seismographs to measure
earthquakes. The more energy that an earthquake releases, the
greater its magnitude. One of the largest earthquakes occurred in Haiti
very recently and killed over 200,000 people
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Finding the Epicenter- Distance Remember P Waves travel faster
than S waves The greater the distance between
the P wave and S wave the farther the source
1) find the time interval between the first P wave and first S wave using the seismogram
2) use the graph to find distance from the seismogram
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Finding the Epicenter- Direction Can use 3 or more
seismograms to do this Create a circle using
direction found on graph Where circles intersect
is the exact location of the epicenter
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Richter Earthquakes are ranked on the Richter Scale – measures amount of energy released 1-10 For each increase of 1.0,
amplitude of the largest surface wave is 10 times greater
About 32 times as much energy is released
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Tsunami Means “Harbor Wave” If an earthquake happens underwater, it can create
a huge wave. This wave travels to the surface After it reaches the surface, it can spread out for
thousands of kilometers in every direction As the wave approaches the shore, it can form a
towering crest that can reach 30m high.
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Earthquake Safety Be prepared – know if an
area has had earthquakes in the past or if it is near a pate boundary.
Make your home earthquake safe
Take heavy objects down from high shelves
Hot water heaters and gas appliances should be securely in place
During earthquakes, stay away from windows or anything that could fall on you.
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Living on a Fault Seismic Safe structures
Resistant to vibrations Buildings with bases of alternating rubber and steel can
withstand quakes of up to 8.3 on the Richter scale without major damage
Buildings and highways can be made so they will bend but not break
Seismic safe structures are more expensive to build than regular structures.
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More Earthquake DamageAnchorage, Alaska 1964 – Magnitude 9.2
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Oakland, CA 1989
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Northridge, CA 1994 – 62 killed
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Former hospital in Mexico City 1985 – Magnitude 8.1 with 7.5 aftershock 18 hours
later
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Turkey 1999