Earthquakes:

1. Earthquakes: How to find where they originate…

2. Terminology: • Epicenter vs. Focus • Focus is the point beneath Earth's surface where rock breaks under stress (or plates shift) and causes an earthquake. • Epicenter is the point on land, directly above the focus

4. Graph vs Gram • Seismograph are instruments that measure and record motions of the ground, including seismic waves generated by earthquakes, nuclear explosions, and other seismic sources • Seismogram is a graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time. • How Seismograph Works

6. S waves vs P waves • P waves • Primary Waves • Named that because they leave the focus first • Travel faster than S waves • Compression Waves • S waves • Secondary Waves • Named that because they leave the focus second • Travel slower than P waves • Transverse Waves • S wave P wave Animation • (slinky)

7. How do we locate earthquakes? • Seismograph data (seismograms) will tell us distance from an earthquake epicenter • We need 3 seismograph readings to find an epicenter

8. 1400 km from Denver, 2600 km from Houston, 4000 km from Miami

9. How do we determine distance? • Lag time between P wave and S wave tells us distance • Fast Runners and Slow Runners...

11. How to read a Seismogram

12. Use lag time to figure out distance traveled

14. Try the activity: • http://www.sciencecourseware.com/VirtualEarthquake/VQuakeExecute.html