Presentation on theme: "Section 21.2. WHAT IS AN EARTHQUAKE? An earthquake is a movement of Earth’s crust caused by a release of energy WHAT CAUSES AN EARTHQUAKE? Eruption."— Presentation transcript:
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
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
Seismograph: an instrument that detects and records earthquake waves P-waves always arrive first, then S-waves, then L-waves
P and S Waves Graph – pg.767 – Under Graphing Skills As distance increases, the travel time for seismic waves increases also.
To locate the exact location of an epicenter, you must have points from three separate seismograph locations around the world
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’)
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/