Aim: What are Earthquakes and their characteristics?

I. Earthquakes – any vibrating, shaking, or rapid motion of Earth’s crust.

A. Fault – zone of weakness or a break in the rock.

1. When the stress exceeds the ability of the crust to resist breaking, the crust shifts and energy is released suddenly.

B. Focus – place underground where break occurs.

C. Epicenter – the location at the surface just above the focus.

D. Seismic waves (shock waves) – earthquake waves

1. Primary (P) waves –the first waves to arrive. Fastest wave that can travel through any material. P-wave animation

Another P-wave animation

2. Secondary (S) waves – second wave to arrive. Slower than P wave and cannot travel through liquids. S-wave animation

Another S-wave animation

P wave motion

S wave motion

E. Measuring Earthquakes

1. Seismometers – detect vibrations of the ground.

2. Seismograph – instrument that detects and records seismic waves.

3. Richter scale – a scale from 1 – 10 that measures the magnitude of an earthquake.

a. Each increase of one unit means a ten-fold increase in shaking.

b. For example, an earthquake that measures a 5 on the Richter scale is 10 times greater than an earthquake that measures a 4 on the Richter scale. An earthquake that measures a 5 on the Richter scale is 100 times greater than an earthquake that measures a 3 on the Richter scale. (5-3=2. 10 x 10 = 100)