JLKP+2.2

Measuring Eathquakes (back to homepage)


 * Vocabulary**

(P Wave) (S Wave)
 * focus**- the point beneath Earth's surface, where rock that is under stress breaks, triggering an earthquake
 * epicenter**- the point on the surface directly above the focus
 * seismic wave**-a vibration that travels through Earth carrying the energy released during an earthquake
 * Primary Wave**- an earthquake squeezes and st5retches the ground like an accordian
 * Secondary Wave**- a kind of wave that vibrates side to side, and up and down
 * surface wave**-a kind of seismic wave that is produced when S and P waves arrive at the center of the Earth
 * magnitude**- the measurement of the strength of and earthquake based on seismic waves and the movements along the faults
 * Mercalli Scale**- a scale that grades an earthquake by the amount of damage they cause
 * Ritcher Scale**- a scale that evaluates seismic waves as measured by a certain sort of mechanical seismograph
 * moment magnitude scale**-a scale that rates earth quakes by estimating the total energy released by a earthquake


 * Outline**
 * ***Seismic Waves***
 * during an earthquake, seismic waves dash out of the focus
 * they carry the energy of an earthquake through the interior, and onto the surface
 * three types:P wave, S wave, and surface wave
 * when these waves touch the Earth's surface at the epicenter, surface waves are produced
 * **Primary Waves**
 * moves straight forward
 * causes buildings to contract and expand
 * they come first
 * can move through solid and liquid
 * **Secondary Waves**
 * they come second
 * move side to side and up and down
 * shakes violently
 * can only move through solids
 * **Surface Waves**
 * when S and P waves come to surface, some become surface wave
 * make most severe ground movement
 * some make the ground move like rolling waves
 * Some make buildings shake side to side
 * **Detecting Seismic Waves**
 * use seismograph to record and measure the vibration and shaking of seismic wave
 * a seismograph needs a pen, a rotating drum, support,and weight
 * during an earthquake, the drum is shaken by seismic waves; the pen stays steady while the drum moves, ao that the pen draws the vibrations
 * now, scientists use electric seismographs
 * **Measuring Earthquakes**
 * at least 20 different measures for rating earthquakes
 * **The Mercalli Scale**
 * in 20 century it was invented to rate earthquakes according to their intensity
 * not precise
 * all 12 steps show how earthquakes affect people, buildings, and land surface
 * the same quake can have different Mercalli rating, because it causes different amounts of damage in different spots

The Mercalli Scale
>> || 3~4 || Unstable objects disturbed (people notice vibrations like those passing from a truck || >> || 5~6 || Slight damage (dishes and windows rattle, books are being knocked off shelves) || >> || 7~8 || Moderate heavy damage (people run outdoors) || >> || 9~10 || Cracks and landslides appear in the ground (buildings that fall off foundations are destroyed || >> || 11~12 || Severe Damage (wide cracks appear in ground,waves visible on surface) >> ---
 * || 1~2 || Almost unnoticeable ||
 * *The Ritcher Scale*
 * measures waves by a certain kind of mechanical seismograph
 * meaures the size of the seismic waves
 * *Moment Magnitude Scale*
 * meaures earthquakes by measuring the total energy released

Diagrams

WD = Wave Direction