Triangulation Activity.

Fresno, CA Seismic Station S-P Interval =
Las Vegas, NV Seismic Station S-P Interval =
Phoenix, AZ Seismic Station S-P Interval =
EARTHQUAKE!!!!! An Earthquake has just occurred in
Southern California! Let’s use these seismograms to find out
Determining the Earthquake Distance
Fresno, CA
S-P Interval Epicentral Distance
___ seconds
Las Vegas, NV ___ seconds
Phoenix, AZ
___ seconds
Where is the Epicenter???
The location of the epicenter determined from your measurements of S-P intervals
"should" be at the point intersection of the three epicentral circles. In general, using this
method to determine an earthquake's epicenter may not result in a precise point.
Discounting measurement errors, there are a number of factors that affect the speed of
earthquake waves. Among other factors, variations in rock types through which the
waves travel will change the actual travel times and hence the S-P intervals. We should
not expect the method of triangulation to result in an exact point.
Let’s see how we did!!
Place an “X” on the epicenter of this Earthquake
Locating the Epicenter
1. How many seismic stations are necessary to locate the Epicenter of an
2. What is the process called of using these stations to pinpoint the epicenter?
3. What types of waves arrive first? Why is that?
4. If 2 Earthquakes occurred, and the time between the p-wave and s-wave for
Earthquake “A” was 30 seconds, and Earthquake “B” was 60 seconds, which
Earthquake was closer?
5. What type of materials can p-waves travel through?
6. What type of materials can s-waves travel through?
7. What did the information from questions 5 and 6 teach us about the interior
of the Earth?
8. Of the 3 types of waves that Earthquakes release, which one causes the most
9. What is the machine that records movements in the Earth called?
10. What is the print out of the Earthquake reading called?
11. What percent of Earthquakes happen in a major Earthquake Zone?
12. Make a list of 3 steps that describe how to locate the epicenter of an
13. What was the magnitude of this Earthquake on the Richter scale?