1 What is an earthquake? Simply put: An earthquake is the shaking of the earth. Free powerpoint...

1 What is an earthquake?

• Simply put:• An earthquake is the shaking of the earth.

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2 - What causes an earthquake?

• Earthquakes are the Earth's natural means of releasing stress.

• Due to the constant motion of the Earth’ plates, this put stress on the edges of the plates.

• To relieve this stress, the rocks tend to bend, compress, or stretch.


An aerial view of the San Andreas fault in the Carrizo Plain, Central California. Picture from www.usgs.gov

http://www.usgs.gov/

3 - Locatin' the Shakin'

• Focus: the place on the Earth’s crust where the pressure was released. Underground.

• Epicenter: the spot on the Earth’s surface directly above the focus.


5 Normal Fault

•Rock above the fault surface moves downward in relation to rock below the fault surface.

•Sierra Nevada fault


6 Reverse Fault• Reverse faults result from

compression forces that squeeze rock.

• If rock breaks from forces pushing from opposite directions, rock above a reverse fault surface is forced up and over the rock below the fault surface.

• Cascadia


7 Strike-slip Fault

• At a strike-slip fault, rocks on either side of the fault are moving past each other without much upward or downward movement.

• The San Andreas Fault is the boundary between two of Earth’s plates that are moving sideways past each other.


8 How does energy created by an earthquake move through the Earth?

•Seismic waves are energy waves that travel outward from the source of the earthquake.


10 P Waves

• Primary waves (P-waves) cause particles in rocks to move back and forth in the same direction that the wave is traveling.

• P-Waves are the fastest waves and are felt first, usually as a bang or a thump.


11 S Waves

• Secondary waves (S-waves) move through Earth by causing particles in rocks to move at right angles to the direction of wave travel.

• These waves are slower than P-Waves and more destructive.

• AKA Transverse waves


12 L Waves

• Surface waves (L-Waves) or land waves move rock particles in a backward, rolling motion and a side-to-side, swaying motion.

• Surface Waves reach the earth's surface after P and S waves.

• Very destructive


13 - How are seismic waves measured?

• Seismic waves from earthquakes are measured with an instrument known as a seismograph.

• Seismographs register the waves and record the time that each arrived.


14 - Measuring Earthquake Magnitude

•Magnitude is a measure of the energy that is released during an earthquake.


15 - Richter Scale

• The Richter magnitude scale is used to describe the strength of an earthquake and is based on the height of the lines on the seismogram.


1 What is an earthquake? Simply put: An earthquake is the shaking of the earth. Free powerpoint...

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