SW US Seismogram

The activity below involves studying three seismograms from an earthquake. You will use the same tools and methods that a seismologist uses to find the epicenter of the earthquake.

  1. Study the three seismograms on the back side of this paper.
  2. For each seismogram, determine the S-P interval and the amplitude.
  3. Use the S-P graph and the S-P intervals to find the distance from the epicenter to each seismic station (epicenter distance).
  4. Determine the epicenter of the earthquake by using a compass to draw a circle around each seismic station. The radius of each circle should be equal to the epicenter distance determined with the S-P graph. The epicenter is the point where all three circles intersect.
s-p distance graph

Seismogram Data Table

Location Amplitude (mm) S-P Interval (seconds) Distance (km)
Reno, NV


Salt Lake City, UT


Flagstaff, AZ



Location Map

map of CA, NV and UT


Reno seismogram
   Salt Lake City seismogram
   Flagstaff seismogram