Earthquakes
Waves and Faults
Causes of Earthquakes
 Plates in earth’s crust
are always moving due
to forces inside the
Earth.
 Forces cause sections
of the crust to move.
 This puts stress on the
rocks.
Causes Cont.
 Rocks bend,
compress and stretch
to relieve that stress
 If the force is great
enough, rock breaks
which make faults
 Rock breaking or
faulting produces
vibrations called
Earthquakes
3 Types of Forces
 Compression – Squeezes
or compresses. Think
two plates colliding
 Tension – Stress causes
stretching. Think two
plates moving up and
down.
 Shear – causes slippage,
rocks move past each
other, side to side.
3 Types of Faults
 Normal – caused by
tension force
 Reverse Fault – caused
by compressional force
 Strike-Slip Fault –
caused by a shear (side
to side) force
Seismic Waves
 Caused by fault
movement
 Vibrations from
released energy
produces waves
 Produces
primary (p-waves),
secondary (s-waves),
and surface (l-waves)
Focus
 Point in the interior
where waves
originate
 Can occur up to 700
km (434 miles) deep
in the Earth.
 Waves travel out in all
directions from the
focus.
Epicenter
 Point on Surface directly
above focus
 P and S waves generated
from focus and generally
travel through the interior
of the Earth
 When waves from focus
reach the Epicenter they
cause Surface waves
 Surface waves travel out
from the epicenter like
ripples on a pond
Seismograph
 Detects seismic
waves, can detect
earthquakes from the
other side of the
world.
Measurement
 Richter Magnitude – measures the energy
released by the earthquake. Base 10 scale
 Mercalli Scale – measures the amount of
damage produced by the earthquake
Primary Waves
 Type – Compressional,
longitudinal
 Speed – Fastest, 1st to
register on seismograph
 Motion – Back and forth
rocking, least destructive
 Movement Through Earth
– Travels through any
material: Solid rock,
magma, water, or air
Secondary Waves
 Type – Shear or transverse
 Speed – Slower, second to
arrive
 Motion – Side to Side
 Movement Through the Earth
– Only through solids.
Liquids and gases can not be
sheared apart
Surface Waves
 Type – Like waves in
Water
 Speed – Slowest, last to
arrive
 Motion – Up/down rolling,
like ripples. Cause the
most damage
 Movement Through Earth
– Through solids and
liquids