Faults: the Break Line Between Two Faces of Rocks, Each Moving in Different Directions

Faults: The break line between two faces of rocks, each moving in different directions.

Earthquakes

1. There is a build up of pressure over time.

2. Plates move and produce stress.

3. Elastic limit: Rocks bend, compress, stretch.

4. If stress is great enough, the rocks break.

5. We feel the vibrations as an earthquake this releases the pressure

6. Most earthquakes occur along tectonic plate boundaries.

7. Seismic waves are sent out in all directions

Faults

Faults can move only a few centimeters a year.

Normal fault: Rocks above the fault move down and the other move up.

Example: Sierra Nevada's.

Reverse fault: Rocks above the fault surface are forced up and the other is forced down.

Example: HimalayanMountains

Strike-slip: Rock on either side are moving past each other.

Example: San Andrea's (LA to SF)

Focus: Point BELOW surface where the rocks actually break – can be very deep.

Epicenter: Point of earth directly above the earthquake focus.

Seismic waves: Energy waves that are sent out from the earthquake center.

Focus:The point in the earth where the waves start.

Primary waves:

1. Called P waves

2. Cause the rocks to move in the same direction out from focus

3. Travel VERY fast.

4. Not as destructive

Secondary waves:

1. Called S waves

2. Waves move out at right angles: Cause the rocks to move in a

perpendicular direction.

3. Slower than P waves and more destructive

Surface waves:LAND/Last

1. Called L waves

1. Generated at the focus, goes to the surface and travels outward.

2. They move the water (soil) particles in a circular motion.

3. Same motion as you get from the ocean swells on a boat.

4. Travel the slowest of all the waves and are the MOST destructive.

Lag Time

1. Difference between the time the first S wave and the first P wave

arrive at the seismic station.

2. The longer the lag time the greater the distance the seismic station

is from the epicenter.