PSNB+2.2

toc =2.2 Measuring Earthquakes=

Vocabulary

 * Focus:** A point under the surface of the Earth, where the rock that s under stress breaks, starting an Earthquake.
 * Epicenter:** A point on the surface of earth, exactly above the focus.
 * Seismic waves:** The viabration that goes through earth holding the energy that has been let go during an earthquake.
 * P waves:** Waves from an earthquake that squeeze or stretch the ground.
 * S waves:** Waves from an earthquake that shake from one side to another, or in an up-or-down motion.
 * Surface waves:** Waves from an earthquake that can make the most dangerous ground movements.
 * Seismograph:** A device that copies the vibrations that come from seismic waves, as they go through earth.
 * Magnitude:** An instrument that measures the movement of seismic waves.
 * Mercalli Scale:** Estimates earthquakes, based on their energy they create.
 * Richter Scale:** Estimates that size of a seismic wave, using a kind of seismograph
 * Moment Magnitude Scale:** Estimates earthquake of all sizes, wherever they are.

Seismic Waves

 * Seismic Waves are like ripples that travel through water, except underground
 * waves travel from the focus, through earth, and to the epicenter.
 * Primary Waves (P waves)**
 * First waves to arrive, compress and expand ground like accordion.
 * Go up and down, side to side, violently shake buildings
 * Secondary Waves (S waves)**
 * After P waves, can't go through liquid (kind of wavy)
 * Go up and down, side to side,violently shake buildings




 * Surface Waves**
 * When P and S reach surface, they create surface waves
 * Slower than P and S, but make severest ground movements

Detecting Seismic Waves

 * Use seismographs:pen writes on roll of paper and moves more when the ground moves more (mechanical)
 * Electronic seismographs record and can also print

Measuring Earthquakes

 * The Mercalli Scale**
 * rates according to intensity and damage; has 12 steps
 * The Richter Scale**
 * Rating of size of seismic waves, not good for big earthquakes
 * The Moment Magnitude Scale**
 * modern; used to measure quakes of all sizes
 * Created with the electronic seismograph

Locating The Epicenter
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 * Scientists look at the seismograph data from different areas and create data from different areas and create at least three wave circles.
 * They then find the center of those circles:the epicenter.