Earthquakes!

**Adapted from www.middleschoolscience.com

What is an earthquake?• Used to describe both sudden slip on a fault,

and the resulting ground shaking and radiated seismic energy caused by the slip

• Caused by volcanic or magma activity, • Caused by other sudden stress changes in the

earth.

Three Types of Faults

Strike-SlipThrust

Normal

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

stress. Stress causes the rock to deform, break, and/or move

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

How Seismographs Work

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

the pendulum remains fixed as the ground moves beneath it

Typical Seismogram

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

Primary Waves (P Waves)

• PUSH-PULL PATTERN! – A type of seismic wave that pushes & pulls the ground

• The FIRST wave to arrive from an earthquake—travels the fastest!

• Travels Parallel to the direction the wave travels

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 (perpendicular) to the direction the wave travels

• Slower!• More destructiveto buildings

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

Comparing Seismic Waves

**P & S Wave song: http://www.youtube.com/watch?v=w3NLexYxR7g

Surface Waves

• Move along the Earth’s surface– ROLL OUT! Motion can be up and down, around &

back & forth

• Travel more slowly than S and P waves– Last to arrive

• Most destructive to structures

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-measures energy

How are Earthquakes Measured? Mercalli Scale-measures damage

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

Earthquake Waves & Earth’s Interior

**See how seismic waves move through the Earth’s layers here (Shadow zone): http://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009page01.cfm

Seismic Waves in the Earth

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

Tsunamis

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

Formation of a tsunami

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

Tsunami Warning System

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