___ 5. The radius of this circle is the epicentral distance. One S - P measurement will produce one epicentral
distance: the direction from which the waves came is unknown. Three stations are needed in order to
"triangulate" the location.
Let’s try it!
An earthquake happened in San Francisco, USA.
Where did it start (epicenter)?

1. and 2. Find the S – P time interval (seconds) for each seismogram below.
1.
Eureka, CA seismic station. S – P time interval=
50
2.
Elko,
NV seismic station. S – P time interval = _
_
72
__
3.
Las Vegas, NV seismic station. S- P time interval=
64
You can now determine the distance from each seismograph station to the earthquake's epicenter using the
known times of travel of the S and P waves.
You need a graph (already prepared for you below!)

S – P Graph
S – P Graph
3.
Use the S-P graph to the left and the estimates you made for the S-P time intervals (see above numbers in
seconds) for the three seismograms (shown again for your convenience) to complete the table below.
The horizontal grid is in one second intervals.
Fill in the table below. Use the numbers from above and the graph to the right.
4. and 5. At this point you would draw the radius of the circles around the seismograph locations (using the
distance in KM from above table). Notice the colours, each circle is around one of the seismograph locations
(Eureka, CA, Elko, NV and Las Vegas, NV) and each location has its own colour (to differentiate the circles).

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- Fall '09
- Drazkiewicz
- Biology, Las Vegas, seismogram, Seismogram Magnitude, Elko Seismogram Magnitude, Eureka Seismogram Magnitude