The document describes the process of using seismic data from three stations to locate the epicenter of an earthquake. The steps include: 1) Recording the arrival times of P and S waves at each station. 2) Calculating the difference between P and S wave arrival times (P-S interval). 3) Using the P-S interval and reference tables to determine the distance from each station to the epicenter. 4) Using the P wave arrival time and travel time to calculate the origin time of the earthquake.

1. To Find The
Epicenter of an Earthquake
Using the Difference in Time
Between the P and the S Wave
Follow the Rainbow!
NSF Funded CUNY GK-12 Science NOW Project Copyright David Stolarz, January 22, 2010

2. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
The Completed Process

3. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
Start Simple – Draw a Line Down From the P-Wave to the Time Scale

4. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
Judge what time the P-wave starts

5. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
08:16 17 18 19
A Quarter after 8 O’Clock! And No Seconds!
A zoom-in shows P-wave starting at approximately 08:16:00

6. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
Put that value in the appropriate box

7. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
Repeat the same process for the S-wave.

8. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
08:21:00 (S-Wave Time)
-08:16:00 (P-Wave Time)
Calculate the interval between the two wave arrivals at the seisomgraph

9. Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.
08:21:00 (S-Wave Time)
-08:16:00 (P-Wave Time)
00:05:00 (Time Difference)
( 0 Hours, 5 Minutes, 0 Seconds )
Enter that time in the appropriate box

10. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Go to page 11 of your Earth Science Reference Tables for the chart shown above

11. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Use the P-S Wave time interval to figure out the distance to the epicenter

12. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Scrap Paper
Place Marks at
P-S Wave Interval
Time and at 0.
Create a reference measurement using scrap paper and the P-S Wave value

13. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Scrap Paper
Scrap Paper
Slide paper up
and over until the
reference marks
Line up with the
P and S Lines.
Find the proper place where the reference marks match the P and S Lines.

14. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Scrap Paper
Lightly, make a
reference mark in pencil
on the reference table
at this place on the P line.
For convenience, make a light pencil mark on the P line for use in the next step

15. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00
B
C
Look straight down from the P line pencil mark and judge the epicenter distance.
.2 .4 .6 .8

16. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km
B
C
Lightly, make
reference marks in pencil
On the reference table
at these two places .
Enter that value for the epicenter distance with proper units.

17. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km
B
C
Look across at the y-axis to Judge the time value
00:06:40
00:06:20
TravelTime(minutes)

18. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20
B
C
Enter that value for the epicenter distance with proper units.

19. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20
B
C
ERASE YOUR MARK!
Erase your pencil mark on the P-wave to keep your reference table clean

20. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20
B
C
08:16:00 (P Arrival Time)
00:06:20 (P Travel Time)
Calculate what time the earthquake happened using the Arrival and travel times

21. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20
B
C
08:16:00 (P Arrival Time)
- 00:06:20 (P Travel Time)MINUS!
Obviously, the earthquake happened earlier than when its was felt miles away

22. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20
B
C
08:15:60 (1 min. is 60 sec)
08:16:00 (P Arrival Time)
- 00:06:20 (P Travel Time)
Convert hours to minutes or minutes to seconds when necessary

23. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B
C
08:15:60 (1 min. is 60 sec)
08:16:00 (P Arrival Time)
- 00:06:20 (P Travel Time)
08:09:40 (Time at Origin)
Put the calculated time of earthquake in the proper box

24. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Anything complex is easier when broken into smaller steps

25. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00
C
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Judge what time the P-wave starts and enter it in the box

26. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00
C
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Repeat the same process for the S-wave.

27. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00
C
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Use the P-S Wave time interval to set reference marks for the sliding step

28. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Create a reference measurement using scrap paper and the P-S Wave value

29. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Find the proper place where the reference marks match the P and S Lines.

30. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Look straight down from the P line pencil mark and judge the epicenter distance.

31. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Look across at the y-axis to Judge the time value

32. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Put the calculated time of earthquake in the proper box

33. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Anything complex is easier when broken into smaller steps

34. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Follow the same overall process for Station C

35. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Judge what time the P-wave starts and enter it in the box

36. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Repeat the same process for the S-wave.

37. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Use the P-S Wave time interval and the y axis of the reference table

38. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Create a reference measurement using scrap paper and the P-S Wave time value

39. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Find the proper place where the reference marks match the P and S Lines.

40. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Enter that value for the epicenter distance with proper units.

41. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Calculate what time the earthquake happened using the Arrival and travel times

42. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
UsingScrapPaper
Finding the Epicenter of an
Earthquake Using the Difference in
Time Between the P and the S Wave
Calculate and place the time of earthquake in the proper box

43. $Z
$Z
$Z
A
C
B
0 5000 km
NSF Funded CUNY GK-12 Science NOW Project
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
3600 km
All three arcs must pass through
the earthquake epicenter, in
this case, the San Andreas fault
in California, USA.
Using scrap paper.
Use the Station info to locate the epicenter of the earthquake on a map

44. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
$Z
$Z
$Z
A
C
B
0 5000 km
On the Station Map, Find Station A

45. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
$Z
$Z
$Z
A
C
B
0 5000 km
Find Station B

46. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
$Z
$Z
$Z
A
C
B
0 5000 km
Find Station C

47. $Z
$Z
$Z
A
C
B
0 5000 km
NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
Distance to the
Epicenter
3.6 x103
km
5.0 x103
km
7.6 x103
km
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
Station
A
B
C
Use the Distance to Epicenter for each station

48. NSF Funded CUNY GK-12 Science NOW Project
Station
Arrival Time of
P-Wave
Arrival Time of
the S-Wave
P-S Wave
Interval
Distance to the
Epicenter
P-Wave Travel
Time
Origin Time of
Earthquake
A 08:16:00 08:21:00 00:05:00 3.6 x103
km 00:06:20 08:09:40
B 08:19:00 08:26:00 00:07:00 5.0 x103
km 00:08:20 08:10:40
C 08:21:00 08:30:00 00:09:00 7.6 x103
km 00:10:20 08:11:40
Distance to the
Epicenter
3.6 x103
km
5.0 x103
km
7.6 x103
km
Distance to the
Epicenter
3,600 km
5,000 km
7,600 km
or
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
Station
A
B
C
$Z
$Z
$Z
A
C
B
0 5000 km
Convert scientific notation for the distance to the epicenter for each station

49. NSF Funded CUNY GK-12 Science NOW Project
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
$Z
$Z
$Z
A
C
B
0 5000 km
Using the scale bar below as the
reference, scribe a circle around
the three points using a
compass, string, or scrap paper.
3600 km
Distance to the
Epicenter
3,600 km
5,000 km
7,600 km
Station
A
B
C
Scribe the arc for Station A using the map scale distance

50. $Z
$Z
$Z
A
C
B
0 5000 km
NSF Funded CUNY GK-12 Science NOW Project
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
The two circles cross at two
points. A third circle is needed
to confirm the earthquake
epicenter.
5000 km
Distance to the
Epicenter
3,600 km
5,000 km
7,600 km
Station
A
B
C
Scribe the arc for Station B using the map scale distance

51. $Z
$Z
$Z
A
C
B
0 5000 km
NSF Funded CUNY GK-12 Science NOW Project
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
3600 km
All three arcs must pass through
the earthquake epicenter, in
this case, the San Andreas fault
in California, USA.
Using scrap paper.
Distance to the
Epicenter
3,600 km
5,000 km
7,600 km
Station
A
B
C
If the distance is longer than the scale, use scrap paper to extend the scale.

52. $Z
$Z
$Z
A
C
B
0 5000 km
NSF Funded CUNY GK-12 Science NOW Project
Finding the Epicenter of an Earthquake
Using the Difference in Time Between the P and the S Wave
3600 km
All three arcs must pass through
the earthquake epicenter, in
this case, the San Andreas fault
in California, USA.
Using scrap paper.
Where the three arcs cross is the epicenter – Circle it!