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Chapter 6 - Earthquakes

Chapter 6 - Earthquakes. What is an earthquake? An earthquake is the vibration or movement of the earth produced by the rapid release of energy in wave form usually along a fault line. These fault lines are typically found at plate boundaries.

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Chapter 6 - Earthquakes

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  1. Chapter 6 - Earthquakes • What is an earthquake? An earthquake is the vibration or movement of the earth produced by the rapid release of energy in wave form usually along a fault line. • These fault lines are typically found at plate boundaries. • The center of an earthquake is called the focus, while the place directly above the focus at the surface is called the epicenter.

  2. Earthquakes: It’s Not My Fault! • At fault lines there is constant motion as one plate slides or moves against another. • Since rocks exhibit elastic rebound, this energy can build up a the rocks compress. • Eventually, the energy is released causing earthquakes while the rocks snaps back much like an elastic band. • The San Andreas Fault is probably the most studied fault.

  3. Fault movement • Three types: • Fault creep – low gradual displacement, hardly noticeable. • Stick-slip – alternating periods of sticking followed by slippage causing rapid release of energy. • Fault scarp – vertical causing cliff formation

  4. Absolutely Shocking! • The adjustments of the bedrock as it settles after an earthquake often results in aftershocks. These are usually weaker than the original quake. • Small minor quakes can precede a major quake and they are called foreshocks.

  5. Seismo Stuff • Seismology – the study of earthquake waves. • Seismologists – the people who do the studying. • Seismographs – instrument used to record quake waves. • Seismograms – the actual print out from a seismograph. See page 160

  6. You Don’t Want to Catch These Waves Dude! • There are two main groups of seismic waves: • Surface waves – these travel along the outer surface of the lithosphere. • Body waves – These are divided into two groups: A. Primary or P-waves B. Secondary or S-waves

  7. P-Waves • P-waves are push-pull waves that cause the volume of the rock to temporarily change. They act on the rock in the same direction the wave is traveling. • They travel the fastest and they travel through all materials. • They are recorded first by seismographs.

  8. S-Waves • S-waves travel slower than p-waves and they act on the rock perpendicular to the direction the wave is traveling. • They temporarily change the shape of the materials they travel through. However, fluids like liquids and gases do not respond to this type of change. Therefore, s-waves can not travel through them.

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