1. Earthquakes The propagation (traveling) of seismic wave through the earth’s interior has provided us with a tool to determine the internal structure of the earth... Recall……..

2. Body Waves P waves – Primary Wave: compression & expansion - push-pull seismic waves sound waves (too low to be heard) fastest (~8 to 9 km/sec) depending on material first to be recorded at a seismograph causes rock particles to vibrate in the same direction the wave is traveling denser the material, the faster the P-wave travels

3. Body Waves S waves – Secondary Wave: shearing (lateral; side to side) seismic wavesshearing (lateral; side to side) seismic waves travels through solid only (3 to 5 km/sec) - NOT liquid or gassestravels through solid only (3 to 5 km/sec) - NOT liquid or gasses second to reach and be recorded at a seismographsecond to reach and be recorded at a seismograph causes the rock particles to vibrate at right angles to the direction of travelcauses the rock particles to vibrate at right angles to the direction of travel

4. Earthquake Machines Seismograph – instrument that detects & records earthquake seismic waves Seismogram – the recording data sheet of an earthquake made by a seismograph

5. http://www.leo.lehigh.edu/projects/seismic/gr aphics/012601_SIndia.jpg

6. Shadow Zone – a wide area around Earth on the side opposite the focus of an earthquake where neither P nor S waves are received