1. SEISMIC WAVE BASICS

2. Finding an Epicenter

3. What is an Epicenter? A point on the surface of the Earth directly above the FOCUS of the earthquake. The point within the Earth from which earthquake waves originate.

5. Use the data from the recording stations: Station A: San Francisco, California P-Wave arrival 3:02:20S-Wave arrival 3:06:30 What is the time difference between P and S wave arrivals?

6. Use the data from the recording stations: Station B: Denver, Colorado P-Wave arrival 3:01:40S-Wave arrival 3:05:00 What is the time difference between P and S wave arrivals?

7. Use the data from the recording stations: Station C: Missoula, Montana P-Wave arrival 3:01:00S-Wave arrival 3:03:00 What is the time difference between P and S wave arrivals?

8. Difference in arrival times: San Francisco: 4:10 Denver, Colorado: 3:20 Missoula, Montana: 2:00

9. TAKE A PIECE OF PAPER, AND MARK OFF THE DIFFERENCE IN ARRIVAL TIME 2800Km 4:10

10. MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S CURVES WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE EPICENTER DISTANCE OF 2800 KM

11. EPICENTER DISTANCES San Francisco: 4:10 Denver, Colorado: 3:20 Missoula, Montana 2:00 2,800km 1100km 2,000km

12. Recording Board Difference in arrival times: San Francisco: 41:0 2,800km 1,000 2,000 3,000 4,0005,000 Open your compass to the EXACT distance on the scale.

13. ...

14. Compare your answer to the historical record

15. Need a closer view to be sure? Go to http://earthquake.usgs.gov/re gional/states.php and retrieve the seismicity map (like the one on the left) for the state containing your possible solution. http://earthquake.usgs.gov/re gional/states.php USGS Based on this map, earthquakes have previously occurred in the region where our epicenter fell. Thus our answer seems likely

16. What if our epicenter had fallen here instead? Does this mean our solution is wrong or less likely? What could help us find out?

17. Credits: This file was originally created by Robert M. DeMarco of Marlboro Central High School Edits have been added by: Chris Visco - Sachem High School Eric Cohen- Westhampton Beach High School Michael Hubenthal - IRIS Consortium