DMTM+2.2

toc 2.2 Measuring Earthquakes

Vocabulary
Seismic Waves- are vibrations that travel through Earth carrying the energy released during an Earthquake.

Focus- is 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.

P waves-are Earthquake waves that compress and expand the ground like an accordion.

S waves-are Earthquake waves that vibrate from side to side, as well as up and down.

Surface waves-move more slowly than P waves and S waves, but they produce the most severe ground movements.

Seismograph-records the ground movements caused by Seimic waves as they move through the Earth.

Magnitude-is a measurement of Earhquake stregth based on seismic waves and movement along the fault.

Mercalli scale-was developed to rate Earthquakes according to their intensity.

Richter scale-is a rating of the size seismic waves as measured by a particular type of mechanical seismograph.

Moment magnitude scale-a rating system that estimates the total energy released by an Earthquake. (The Moment magnitude scale can be used to rate Earthquakes of all sizes, near or far)

Seismic Waves

 * Primary waves
 * "P" Waves
 * first to arrive


 * Secondary Waves
 * "S" Waves
 * second to arrive

Surface Waves

 * More powerful than p waves and s waves

Detecting Seismic Waves

 * Electronic mechanical Seismograph

Measuring Earthquakes

 * Mercalli Scale
 * The Richer Scale
 * Moment magnitude scale
 * Magnitude

Locating the Epicenter

 * Measuring both waves
 * there is a difference