When an earthquake occurs seismic waves are sent out in all
directions. Earthquake waves come in three main types: P-waves (primary);
S-waves (secondary); and L-waves (surface). These waves travel at different
In this activity you will use seismographic data and a compass to find the epicenter of an earthquake.
1. Calculate the time difference for when the waves were received at each station.
2. Use the Graph to find the distance from the station to the epicenter.
3. Using the scale on the map, draw a circle around each station, with a radius of the
circle equal to that station's distance from the epicenter.
4. Mark the point of intersection for all circles: this is where the earthquake occurred.
P-wave arrival S-wave arrival
Seismograph Station Data
P-wave arrival: 10:05 AM
S-wave arrival: 10:08 AM
P-wave arrival: 10:10 AM
S-wave arrival: 10:14:30 AM
P-wave arrival: 10:13 AM
S-wave arrival: 10:20 AM
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