1. Earthquakes & Waves SF 1906 LA 2008 Haiti 2010 Mexico City 1985

2. Where & how earthquakes occur  Occur at plate boundaries  Caused by the movement of tectonic plates  Energy is released in seismic waves

3. Stress builds at plate boundaries until released Raise your hand if you have been on the Earthquake trail in Point Reyes. What happened to the fence?

4. Where Earthquakes Start  They start under ground at the focus.  Waves travel outward from focus in all directions.  The point on the surface, directly above the focus is the epicenter. Pair share: when have you seen waves moving outward as a circle?

5. Tsunami  When an earthquake occurs in the ocean it can generate enormous waves of water called Tsunamis. The 2004 Tsunami kill 300,000 people and caused $123 Billion in damage.

6. About Waves Parts of a Wave Crests: highest point Troughs: Lowest point Amplitude: ½ the distance from crest to trough Pair share: how many crests will seismo the surfing dog pass over?

7. Wave terms  Wavelength: distance from crest to crest  Period: time it takes for one full wavelength to to pass by  Frequency: the number of waves passing in a given time Pair share: how many wavelengths will Echo the surfing dog pass over?

8. Types of Seismic Waves  Longitudinal: ( P waves) Fastest, travel like a spring through rock  Transverse ( S waves) slower, move like a shaken rope  Surface waves: move out in circles from epicenter in a rolling motion, damaging to structures

9. Seismic wave motion P: primary meaning 1 st S: Slower, second

10. Detecting earthquakes  Seismographs: pendulums record motion onto paper  3 seismographs in different locations can pinpoint the epicenter.  Epicenter: where P, S, and surface waves meet

11. Measuring the magnitude  Richter scale: rates the energy generated by an Earthquake.  Each level is 10 X greater than the next  Most are very small, not felt  Mercalli index: the amount of shaking felt.

12. Review 1) How is the energy from earthquakes transferred? 2) What scale is used to measure the magnitude of an earthquake? 3) What kind of wave causes the most damage?