Features of Earthquakes Chapter 11, Section 2 Prince William Sound, Alaska March 28, 1964 Magnitude 9.2

Denali Fault Earthquake M7.9 November 3, 2002

The survival of the Trans-Alaska Oil Pipeline in the 2002 Denali Fault earthquake demonstrates the value of combining careful geologic studies of earthquake hazards and creative engineering in designing and protecting such important structures and lifelines.

What are Earthquakes? As rocks slide past each other along a fault, rough areas can cause the rock to become stuck. As rocks slide past each other along a fault, rough areas can cause the rock to become stuck. Energy builds up in this “stuck” part of the rock. Energy builds up in this “stuck” part of the rock. When enough energy builds up, the rock reaches the elastic limit and moves a large distance in a short amount of time. When enough energy builds up, the rock reaches the elastic limit and moves a large distance in a short amount of time. When this movement occurs, energy is released in the form of seismic waves. When this movement occurs, energy is released in the form of seismic waves.

Seismic Waves 3 main types: 3 main types: –Primary waves –Secondary waves –Surface waves

Seismic Waves Primary Waves (p-waves) Primary Waves (p-waves) –Cause particles in rocks to compress and then stretch apart (in the same direction the wave travels). –Fastest type of wave.

Seismic Waves Secondary Waves (s-waves) Secondary Waves (s-waves) –Cause particles in rocks to move back and forth (at right angles to the direction the wave travels).

Seismic Waves Surface Waves Surface Waves –2 types. –Cause rock particles to move in backward rolling motion and a side to side swaying motion. –Only travel on the surface of the earth. –Slowest type of wave.

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