Chapter 8 and 9
What causes an earthquake ?
Earthquakes are caused by the vibrations of Earth produced by the sudden release of energy
Describe the location of an epicenter and focus.
Epicenter is the location of the surface of Earth directly above the focus.
Focus is the point within the Earth where the earthquake starts.
What is the elastic Rebound hypothesis ? How does it relate to earthquakes ?
Elastic rebound hypothesis is the release of built-up energy. Most earthquakes are produces by the release of elastic of elastic energy stored in rocks that has been subjected to great forces.
Describe aftershocks and foreshocks.
Aftershocks are small quakes that come after a major earthquake.
Forceshocks are small quakes that come before a major earthquake.
How are earthquakes measured ?
Historically, scientists have used two different types of measurement to describe the size of an earthquake–intensity and magnitude.
Describe the following earthquake waves: surface, S waves, and P waves.
Surface waves=seismic waves that travel along earth’s outer layers. They move up, down, and side to side. Most destructive earthquake wave. Last to arrive at the seismograph

S waves=shake particles at right angles to their direction of travel. Also known as traverse waves. Can only travel though solids. Slower than P waves but faster then surface waves.

P waves=They push ( compress ) and pull ( expand ) rocks in the direction the wave travels. Also known as compression waves. Can travel through solids, liquids & gas. Fastest waves (arrive 1st to the seismograph)

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The order would be P,S,Surface.

How do scientist locate earthquakes?
(distance and directions)
The difference in velocities of P waves provides a way to locate the epicenter. Scientists use a travel-time graph, in which one needs at least 3 seismograph station data.
Where do most earthquakes occur ?
Most of these earthquakes occur around the outer edge of the Pacific Ocean. This zone is known as the circum-Pacific belt. Active earthquake area in this zone include Japan, the Phillipiness, chile, and Alaska’s Aelutian Islands.
Describe each of the different scale used to measure earthquakes. Which one measures intensity and which one measures magnitude? What is the difference between magnitude and intensity ?
Richter Scale=measures the magnitude of an earthquake. Based on the amplitude of the largest seismic wave. A ten fold system. News reporters use this scale, but scientists no longer use this scale.
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