EPSC201 - Lecture 5 Notes
Four basic types of seismic waves
Two classes – Body waves and surface waves
Body waves are small amplitude and don’t do much damage, they travel underground
• P waves – force and propagation go in the same direction, like pushing a slinky forward and back-
• S waves – force is 90 degrees to propagation, its analogous to waving a string that is tied at the
Surface waves are responsible for all the earthquake damage and do all the damage, They have the
Love waves – shear waves of up/down and side to side Raleigh Waves – rolling action Seismographs:
The frame is attached to the ground while a weighted spring with a pen on it makes a record on a paper.
The weight doesn’t move while the frame does. The left one on the diagram measures vertical movement,
while the one on the right will measure horizontal measurements.
Modern seismographs use a magnet around a coil, and when the magnet moves up and down it creates a
The P wave travels faster then the S wave. The further the earthquakes epicenter is, the greater the differ-
ent in time of arrival.
The surface waves will arrive after the internal waves (longer distance to travel)
The speed on which the waves travel depends on the medium the waves travel through. The mantle is
more dense then the crust. The more dense the material, the faster the seismic wave arrives.
The Richter scale is a measure of amplitude of the waves read by a seismograph. It is a logarithmic scale.
This means that and 8 is ten times larger then a 7. Each 1 in magnitude is ten times bigger. A 5 and above
is classified as a risk. 7 and above cause serious dam