1. How do we find the distance to the epicenter from a station?

2. Based on studying many earthquakes…
Scientists were able to come up with a distance travel-time graph for earthquakes
ESRT.Slides.pdf
This graph tells you at varying distances to the epicenter how long it would take a P wave or S wave to get to that station

3. WHAT YOU NEED
A seismogram which tells you the arrival time of P and S waves
The lag time ( difference in arrival time between P and S waves
ESRT

4. From the seismogram figure out the arrival time of the P and S wave
WHAT YOU DO
From the seismogram figure out the arrival time of the P and S wave
                                                                   

5. Subtract the P wave arrival time from the S wave arrival time
To get the lag time…
Subtract the P wave arrival time from the S wave arrival time
             

6. Represent the lag time on paper

7. Fit the paper between the lines and read down
New York State High School Regents Exam Prep Center: Earth Science
                                                                            
                                                                                                                                                                                                                                   .
Fit the paper between the lines and read down

8. TRY THESE
A P wave came into a station at 02:05:00. The S wave came in at 02:10:00. What is the distance from the epicenter of an earthquake for this station?

9. 02:08:00- 02:05:00=5 minute lag time LOOK back to slide 6

10. A P wave came in at 1:05:30. The S wave came in at 1:08:50
A P wave came in at 1:05:30. The S wave came in at 1:08:50. How far is this station from the epicenter of the earthquake?

11. If a station is 2000 km from an earthquake epicenter, how long would it take a P wave to get to that station?
What about the S wave?

12. A P wave came into a station at 03:10:00
A P wave came into a station at 03:10:00. The S wave came in at 03:17:00. How far is this station from the epicenter of the earthquake?
What is the lag time?

13. 7 minutes
Represent it on paper-
slide the paper between the lines-
line it up
and read down-
that is your distance
Remember units

14. How do we find an epicenter?
You must have 3 seismograms b/c one seismogram only gives you the distance to the epicenter it does not pin point the exact location.

15. Drawing Circles to represent distance to the epicenter
Use the distance to the epicenter provided by one seismogram and scale to set your compass
Draw a circle around your given city with that radius.
Repeat this for 2 more stations
The Epicenter could be at any point on this circle to narrow down the location you need 2 more circles
Distance to
the
epicenter

16. Epicenter – will be where the 3 circles intersect