 Waves of energy that travel through the earth after rock has been elastically deformed 1. The crust layer is stressed and begins to deform 2. If the crust breaks it releases energy 3. The energy waves travel through the earth to the surface

 Body waves – seismic waves that travel through the earth’s interior which include: 1. Primary waves (P) 2. Secondary waves (S)  Surface waves (L) – Long waves, travel on the surface 

 Waves that spring back and forth until the rock goes back to its original or new shape  Travel through solids, liquids and gasses  Are the fastest  First to be detected 

 Waves travel side to side after rock is back in original or new position  Second fastest  Cannot travel through liquids or gasses  Called secondary or shear waves

L WAVES = LAST TO ARRIVE!  Waves travel along the surface  Travel more slowly but are more destructive  Most damage comes from surface waves  Move the ground up and down and in circles SURFACE WAVES = L WAVES

EPICENTER AND FOCUS SEISMOGRAPH – RECORDS SEISMOGRAMS  The FOCUS is the earthquakes starting point  The EPICENTER is the point on the earth’s surface directly above the starting point (focus)

Scientists collect several seismograms of the same earthquake from different locations  They calculate the arrival time difference between the S and P waves  They plot these differences on a time distance graph to determine the distance of the epicenter to the recording seismograph TIME/ DISTANCE GRAPH

 Using the data from the time distance graph scientists can calculate the radius of the area the waves travel  Then scientists construct the diameter of each area and where they all overlap is the epicenter

 When another earth- quake occurs at the same epicenter shortly after the first earth quake  Not usually as strong  Sometimes occur a few days after the initial earthquake  Can cause damage!