THEY+2.2

toc =2.2 Measuring Earthquakes=

**Vocabulary**

 * focus:** points under the Earth's surface where rocks break under a stress force and as a result, causing an earthquake.
 * epicenter:** points on the surface of the Earth that is directly over the focus of the Earth.
 * seismic waves:** a vibration travels through the Earth carrying the energy that was released during when an earthquake striked.
 * p waves:** a seismic wave that compresses the ground as a result it expands the Earth's surface.
 * s waves:** a seismic wave that moves the Earth's surface vertically and horizontally.
 * surface waves:** a different type of seismic wave that occurs when the P waves and S waves reaches the surface of the Earth.
 * seismograph:** a device that records the movements of the ground caused by the seismic waves they travel through the Earth.
 * magnitude:** the measurement of an earthquake strength based on the movements along faults created by the seismic waves.
 * Mericalli scale:** a scale that rates earthquakes according to how much damage they cause by their intensity.
 * Richter scale:** a scale that rates seismic waves as by being measured by a certain type of mechanical seismograph.
 * moment magnitude scale:** a scale that rates earthquakes by estimating the total amount of energy released from the earthquake.

**Seismic Waves**
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 * seismic waves are vibrations that is carrying energy that was released from the Earth
 * seismic are ripples that travel through Earth's crust
 * Primary Waves**
 * The P Waves are primary waves
 * The P Waves expand in the ground
 * Secondary Waves**
 * After the P Waves the S Waves Come
 * When an earthquake occur, the S Waves vibrate from side to side
 * Surface Wave**
 * After the P and S Waves reach the surface of the earth
 * more slower than the P and S Waves, but creates more critical damage than the P and S Waves

Detecting Seismic Waves

 * for detecting seismic waves geologists use seismographs
 * seismographs measure the movement of an earthquake created by a seimic wave throughout the earth

Measuring Earthquakes

 * there are 20 unique types of measures for rating earthquakes with their own strengths and shortcomings
 * three of the ways of measuring earthquakes are the Mercalli scale, the Richter scale, and moment magnitude scale
 * The Mercalli Scale**
 * this scale records the intensity of an earthquake
 * these measurements are not exact because the intensity rate might change at times
 * The Ritcher Scale**
 * the Richter scale measures the size of the seismic waves
 * the scale might have an exact measurement on short distances, but long distant measurements are incorrect
 * The Moment Magnitude Scale**
 * The Moment Magnitude Scale estimates the total energy that was sent out by an earthquake
 * the moment magnitude scale can measure earthquakes that are small or large and earthquakes that are near or far

**Locating the Epicenter**

 * geologist draw circles on certain seismograph areas on the radius of each of the following circle is the distance from the seismograph all the way to the epicenter
 * this calculation does not always set where the epicenter really is.