Key Terms: seismology,focus, epicenter, seismic waves, P waves, S waves, surface waves

Seismology Please turn to page 111 in your textbook. Word origin : From the Greek language. A combination of 2 Greek words Seism: From the Greek word seismos (earthquake). Derived from the word seiein (to shake). ology: The Greek word for the study of “something”. 2

Where Earthquakes Begin Earthquakes always begin in rock below Earth’s surface. Most begin in the lithosphere within 100 km of Earth’s surface. Always start at one particular point. 3

Earthquake Focus and Epicenter Focus The point beneath Earth’s surface where rock that is under stress breaks triggering an earthquake. Epicenter The point on Earth’s surface directly above the focus of the earthquake. 4

Earthquake Focus and Epicenter 5

Seismic Waves When an earthquake occurs, a tremendous amount of energy is immediately released. The energy travels in all directions away from the focus. The energy travels away from the focus in waves. These waves are known as seismic waves. Lets observe the animation. 6

Types of Seismic Waves There are three types of seismic waves. Primary Waves (P waves). Secondary Waves (S waves). Surface Waves. An earthquake sends out P and S waves from its focus. When these waves reach the epicenter, surface waves develop. 7

Primary Waves Known as P Waves Also known as compression waves. Characteristics: Travel the fastest of all the waves. Can travel through liquids. Compress and expand the ground. 8

Secondary Waves Known as S waves. Characteristics: Travel slower than P waves. Cannot travel through liquids. Vibrate in a wave motion (side to side or up and down). Also known as shear waves. 9

Surface Waves Characteristics: Occur when P and S waves reach the epicenter. Travel across Earth’s surface slower than P and S waves. Produce the most ground movements. 10

Wave Speed The three seismic waves travel at different speeds. P Waves are the fastest. S Waves are second. Surface waves are the slowest. 11