12/14/15
 Earthquake
 Sudden, violent shaking
of the ground due to
movement of tectonic
plates
 “Seismos”
 Greek word meaning to
shake
 Seismology
 Study of earthquakes
 Seismologist
 Scientist that studies
earthquakes
 Seismic waves
 Waves of energy that
travel through Earth
during an earthquake
 Seismograph
 Instrument used to
record earthquakes
 Produces seismograms
 Ancient Greeks thought
strong winds blowing
through lots of
underground caverns
caused earthquakes
 Up to 17th century
people thought large,
restless creatures
underneath the surface
caused earthquakes
 Most earthquakes take place near tectonic plates
 Convergent: strong e-quakes, deep in Earth’s crust
 Divergent: weak, shallow (near surface of Earth’s crust)
 Transform: moderate, shallow
 Movement of plates results in rock deformation
Plastic Deformation
Elastic Deformation
 Does NOT lead to
 Does lead to earthquakes
earthquakes
 Rock layers fold like clay
 After pressure from
plates is released, rocks
stay in folded shape
 Rocks bend and stretch
like rubber bands
 Elastic Rebound occurs
when pressure is
released
 Rock snaps back to
original shape
 Two main types
 Body Waves: travel
through the Earth
 Surface Waves: travel at
Earth’s surface (obviously)
 Waves travel at different
speeds and move material
they travel through
differently
 P – Waves:
 Primary (arrive first, travel
fastest)
 Pressure (squeeze and
stretch rock layers)
 Can travel through solids,
liquids, gases
 S – Waves:
 Secondary (arrive second,
travel slower)
 Shear (swing side to side)
 Can only travel through
solids
 Surface Waves (or L –
Waves):
 Slower than Body Waves
(P & S Waves)
 Travel along top of
Earth’s crust
 Move ground in circular
motion (like a roller
coaster)
 Most destructive
(damage) seismic wave