Earthquakes

What is an earthquake?

• Used to describe the sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip

• Caused by other sudden stress changes in the earth.

Plate Tectonics

• The Earth’s crust is made of giant plates of rock floating on the liquid mantle (interior of earth)

• The plates move on the mantle; some places spreading apart, some places coming together, and some places sliding past each other

• A fault is a line where the plates touchhttp://www.pbs.org/wgbh/aso/tryit/tectonics/intro.html

What causes earthquakes?• Tectonic plates move past each other causing

stress. Stress causes the rock to deform– Elastic deformation – rock stretches then reaches

a breaking point, releasing energy.

Elastic Rebound – deformed rock goes back to its original shape

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Focus – point inside the Earth where an earthquake begins

Epicenter – point on Earth’s surface above focus

Primary Waves (P Waves)

• A type of seismic wave that compresses and expands the ground

• The first wave to arrive at an earthquake

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Secondary Waves (S Waves)

• A type of seismic wave that moves the ground up and down or side to side

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Comparing Seismic Waves

Surface Waves

• Move along the Earth’s surface• Produces motion in the upper crust

– Motion can be up and down– Motion can be around– Motion can be back and forth

• Travel more slowly than S and P waves• Most destructive part of an earthquake

Typical Seismogram

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

How do scientists calculate how far a location is from the epicenter of an earthquake?

• Scientists calculate the difference between arrival times of the P waves and S waves

• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

How are Earthquakes Measured? Richter Scale

How are Earthquakes Measured? Mercalli Intensity Scale

Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

Earthquake Waves & Earth’s Interior

Seismic Waves in the Earth

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM