1. Section 21.2

2. WHAT IS AN EARTHQUAKE?  An earthquake is a movement of Earth’s crust caused by a release of energy WHAT CAUSES AN EARTHQUAKE?  Eruption of a volcano  Collapse of a cavern or building  Major cause – stress between two plates

6.  Friction builds up between two plates  The stress causes the plates to deform or ‘stretch’  Eventually, the stress becomes great enough that it overcomes friction and the plates move  The plates ‘snap’ back into their original shape and begin building up friction again

8.  Point on the fault (or plates) where movement first occurs  Where an earthquake starts  3 types  Shallow (0-70km)  Intermediate (71-300km)  Deep (301km and higher)

9.  Point on the Earth’s surface directly above the focus  What is reported as the location of an earthquake

10.  P-waves: primary waves; travel through solids, liquids, and gases; back and forth motion  P waves are ______________ waves.

11.  S-waves: secondary waves; travel through solids only; side to side motion (snake)  S waves are ___________ waves

12.  L-waves: surface waves  Combination of up and down and back and forth motion  Cause the most damage due to their rolling action and long wavelengths

15.  Seismograph: an instrument that detects and records earthquake waves  P-waves always arrive first, then S-waves, then L-waves

16.  P and S Waves Graph – pg.767 – Under Graphing Skills  As distance increases, the travel time for seismic waves increases also.

17.  To locate the exact location of an epicenter, you must have points from three separate seismograph locations around the world

18.  Richter Scale  Developed by Charles Richter in the 1940’s  Measures the amount of energy released by the earthquake itself  Scale from 1-10 (weakest - strongest)  Each number is 32 times stronger than the next lower number (Ex: ‘6’ is 32 times stronger than a ‘5’ and 1024 times stronger than a ‘4’)

21.  We cannot predict earthquakes other than giving periods of time in which we think they will occur.  Earthquakes are most common along sliding plate boundaries, but they can occur in other places.  http://earthquake.usgs.gov/learn/kids/ http://earthquake.usgs.gov/learn/kids/