Seismology
• Seismology is the branch of science devoted
to studying Earthquakes. A seismologist is a
scientist who studies earthquakes.
Where do Earthquakes happen?
• Earthquakes usually happen along the edges
of tectonic plates. They occur along faults.
What causes Earthquakes?
• Plastic deformation (folding, bending) does not
cause earthquakes… elastic deformation does.
When the rock is stretched too far it will break.
The breaking is what causes Earthquakes.
Elastic Rebound
• Sudden return of elastically deformed rock to its
original shape is called elastic rebound. Energy is
released and some of it travels as seismic waves.
These cause the earthquake.
Earthquake zones are places where a large number of faults
are located. An examples is the San Andreas fault zone in CA.
Earthquakes can happen along any type of plate boundary, and
can also happen along faults in the middle of plates.
How do earthquake waves travel?
• Seismic waves are energy waves that travel
through the earth. If they are inside the earth,
they are called seismic body waves.
• It they are at the earth’s surface, they care
called seismic surface waves.
• P Waves – Pressure or primary Waves that travel through solids,
liquids, and gasses. They are the fastest, so they travel ahead.
Moves back and forth. (body)
• S Waves – Shear or secondary waves. Cannot travel through liquid
and always arrive after P waves. Side to side. (body)
• Surface Waves – Cause motion mostly in the upper few KM of
earth’s crust. Travel more slowly and are more destructive than
body waves. Can move up and down or side to side.
Surface Wave