Earthquakes

Ch. 7 Earthquakes

The vibration of Earth produced by the rapid release of energy.

Earthquakes are normally associated with large fractures in the Earth’s crust called faults.

How do earthquakes occur?

1. We have faults or a fault in the area

2. Tectonic forces slowly deform crustal rocks on both sides of the fault

3. These forces cause the rocks to bend(stress and strain) and store elastic energy

4. Eventually, the rocks can’t bend anymore and slippage occurs at the weakest point along the fault(focus).

5. This slippage causes displacement and the strain/stress along the fault to be released

6. When the rocks “snap” back to their normal position, vibrations in the form of primary and secondary waves are released causing an earthquake.

One of the most famous faults is the San Andreas fault in California. The 1994 quake only lasted 40 seconds, but killed 61 people and did $15 billion worth of damage. Was a 6.6-6.9 on the Richter Scale

How Earthquakes are measured

Seismographs record earthquake waves and are read by looking at the seismogram. These seismograms record three types of waves: Primary waves(p-waves), Secondary waves(s-waves), and Surface waves. The two most important are the p and s waves.

P-waves

1. Known as push-pull waves(compress and expand rocks changing volume)

2. The relative movement is a back-forth motion

3. Travel faster than S-waves

4. Can travel through solids, liquids, and gases

S-waves

1. Known as oscillating waves that cause particles to oscillate at right angles to the direction of wave motion(changes shape of material).

2. The relative movement is an up-down motion

3. Slower than P-waves

4. Can travel through solids, but not liquid and gases(they don’t respond to changes in shape)

Surface waves

1. Complex movment up and down and oscillation like s-waves, only horizontally

2. Slower the p and s...