5.8 NOTES
What are the different kinds of seismic waves?
Objective: Describe the three kinds of seismic waves
The fastest moving seismic waves are primary waves, or P waves. P waves are
push-pull waves that cause particles in materials to move back and forth in place.
P-waves can move through SOLIDS, LIQUIDS, and GASES
Secondary waves, or S-waves, are the second wave to be recorded by a
seismograph. S-waves move slower than P-waves, and move through SOLIDS
ONLY. They move side to side
Surface waves, or L-waves, are the longest and last waves to be recorded. Lwaves travel through solids, and since they are long and near the surface, cause
the MOST DAMAGE.
A seismogram tells scientists a great deal about earthquakes. For example, it can
indicate how far away the epicenter of an earthquake is and the force of the
earthquake. P-waves arrive before S-waves. The distance between the arrival
times of P-waves and S-waves is called an S-P interval. Using this time difference,
scientists can tell how far the epicenter is from the seismograph
S-P INTERVALS AND DISTANCE
S-P Interval
1 min
2 min
3 min
4 min
5 min
Distance from Epicenter
700 km
1200 km
1800 km
2500 km
3400 km
To find the epicenter, seismographs from three stations are needed. By drawing a
circle around each station, the diameter is used to represent travel time. The
place where the three circles cross is near the epicenter.