6-2 Earthquakes and Seismic Waves

P waves

P waves are seismic waves that compress and expand the ground like an accordion; they are the first waves to arrive in an earthquake

S waves

S waves are seismic waves that vibrate from side to side as well as up and down, shaking the ground back and forth; they arrive after P waves and are also known as secondary waves. S waves can NOT travel through liquids

moment magnitude scale

The rating system that estimates the total energy released by an earthquake

magnitude

a number geologists assign to an earthquake based on the earthquakes size, after measuring seismic waves and fault movement.

Richter scale

a rating of an earthquake's magnitude based on the size of the earthquake's seismic waves.

seismograph

an instrument that records and measures seismic waves.

focus

area beneath Earth's surface where rock that is under stress breaks, triggering an earthquake

surface wave

occurs when some P waves and S waves reach the surface. Surface waves move more slowly than P and S waves and can make the ground roll like ocean waves or shake buildings from side to side.

Mercalli scale

scale developed to rate earthquakes according to how much damage was done to homes and other buildings in a given place.

epicenter

the point on the surface, directly above the focus of an earthquake

earthquake

the shaking and trembling that results from the movement of rock beneath Earth's surface