EarthquakesEarthquakes

What is an earthquake?What is an earthquake?

• The shaking and trembling that results from the movement of rock between the Earth’s surface.

FaultFault

• A break in Earth’s crust where slabs of crust slip past each other.

Where do faults occur?Where do faults occur?• Faults usually occur along plate boundaries,

where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks.

3 types of faults3 types of faults1. Strike slip fault2. Normal fault3. Reverse fault

Strike-Slip FaultStrike-Slip Fault• Rocks on either side of the fault

slip past each other sideways with little up-or-down motion.

Normal FaultNormal Fault

• The fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault.

Reverse FaultReverse Fault

• Has the same structure as a normal fault, but the blocks move in the opposite direction.

Faults in ActionFaults in Action

TsunamisTsunamis• A large wave produced by an

earthquake on the ocean floor.

Measuring EarthquakesMeasuring Earthquakes

Seismic WavesSeismic Waves• Vibrations that

travel through Earth carrying the energy released during an earthquake.

1. Primary Waves2. Secondary

Waves3. Surface Waves

Primary Waves (p waves)Primary Waves (p waves)

• The very first waves to arrive.• They compress and expand the ground

like an accordion.

Secondary Waves (s waves)Secondary Waves (s waves)

• Come after the primary waves.• Vibrate from side to side as well as

up and down.

Surface WavesSurface Waves

• Form when S and P waves reach the Earth’s surface.

• Produce the most severe ground movements.

Richter ScaleRichter Scale• Developed by Charles Richter in 1935.• Rating of the size of seismic waves as

measured by a particular type of seismograph.