LPKW+2.2

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=2.2 Measuring earthquakes=

Vocabulary

 * focus**-the point below the earths surface where rocks under stress break causing an earthquake
 * epicenter**-the point directly above the epicenter
 * seismic waves**-vibrations in the earth carrying energy during an earthquake
 * P waves**-waves that compress and expand the ground
 * S waves**-waves that vibrate side to side and up and down
 * surface waves**-waves that reach the surface
 * seismograph**-devices that records the vibrations of seismic waves
 * magnitude**-a measurement of earthquake strength based on seismic waves and movement along faults
 * Mercalli scale**-a measurement that was developed to rate the intensity of earthquakes
 * Richter scale**-a rating o the size of seismic waves
 * moment magnitude scale**- a rating system that estimates the total energy released by an earthquake

Seismic waves

 * Primary waves**
 * compress and expand the ground
 * can travel trough water
 * **Secondary waves**
 * moves the ground back and forth so as up and down
 * shake structures violently when they reached the surface
 * **surface waves**
 * happens when P and S waves reach the surface
 * shakes the gound most violently

Locating the epicenter

 * The farther from the epicenter, the greater time of the arival of P waves and S waves