# 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.

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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 touch http://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 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

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