3. 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.

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

7. P wave motion

9. S wave motion

11. E. Measuring Earthquakes 1. Seismometers – detect vibrations of the ground. 2. Seismograph – instrument that detects and records seismic waves.

12. 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)