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toc =Measuring Earthquakes=

Vocabulary

 * focus**- the place in the earth where stress releases
 * epicenter**- the place above the focus
 * seismic waves**- the thing that carries energy caused by an earthquake
 * primary waves**- waves that diverge and squeeze rock
 * secondary waves**- waves that move up and down
 * surface waves**- come after p and s waves, but are mare destructive than both
 * seismograph**- senses vibrations in the earth
 * magnitude**- the analysis of the energy released, mostly waves along the cracks in the earth
 * mercalli scale**- a scale made to measure the strength of the earthquake
 * ritcher scale**- a scale made to rate the waves measured by another type of tool
 * movement magnitude scale**- a tool that guesses the complete power used in a quake

Seismic waves

 * Seismic waves
 * causes vibrations when stress is released
 * that point is the focus, above is the epicenter
 * vibrations cause earthquakes
 * move like ripples in a pond
 * vibrations/earthquake is strongest at the epicenter
 * three types of seismic waves, P waves, S waves, surface waves
 * Primary Waves (P waves)
 * compress and expands ground
 * particles of the crust vibrate forward and back along the path of the wave
 * Secondary Waves (S waves)
 * moves ground up and down, and side to side
 * shakes back and forth
 * shakes structures hard
 * cannot shake liquid
 * Surface waves
 * move more slowly, but make the strongest movements in the ground
 * come slower than P or S waves
 * Shakes buildings from side to side
 * some P and S waves are transformed into surface waves



Detecting Seismic waves

 * seismograph
 * tool for recording earthquakes
 * detects ground movements, needle with pen on it shakes and writes the vibrations
 * we use electronic ones now

Measuring Earthquakes

 * Magnitude
 * system that measures the strength of an earthquake
 * three main ways of measuring earthquakes: Mercalli scale, Richter scale, and the moment magnitude scale
 * Mercalli scale
 * measures quake on its intensity in one place
 * tells how it affects the land
 * Richter scale
 * recorded by special seismograph
 * used for about 50 years
 * accurate for smaller, nearby quakes
 * Moment Magnitude Scale
 * finds amount of energy released at focus
 * can tell earthquakes near or far
 * also uses electronic seismograph

Locating the Epicenter

 * Seismic waves timings
 * P waves, then S, than a while later Surface waves
 * to find the epicenter scientists find the difference between the arrival time of the P and S waves
 * more split apart the two timings are the farther the epicenter
 * creates three circles, in middle of each there is a seismograph, where circles meet is the epicenter

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