Download Chapter 12-1

How and Where Earthquakes
Happen
 Movement
of
ground caused
by a sudden
release of
energy
 Movement
along faults
 Rocks
under
stress suddenly
shift along faults
 Stress
caused
faults to break
 Return
of
elasticity from
deformed rock
to original
shape
 Rebound back
into shape
starting from
weakest point
 Focus – point of
1st motion of a
quake
• 90% shallow
 Epicenter
– point
on surface above
the focus
• Most damage
0
km – 70 km are
shallow
• Most damage. WHY?
 70km
– 300 km are
intermediate
 300
km – 650 km are
deep




Travel in all
directions
Body wave –
travel through the
body of them
medium
Surface wave –
Travel on surface
of material NOT
through the
middle
Vibrations are
called seismic
waves
 waves
travel at
different speeds
 P wave – Primary or
compression
• Fastest
• Move through solids,
liquids, & gases
• The more ridged the
material the faster
they move
S
wave – Secondary
• 2nd fastest
• Side to side motion
• Only travel in solids
 Shallow
faults
 Slowest
 Cause
Greatest
Damage
 2 types
• Love – side to side
• Rayleigh - rolling
 Useful
in
determining
the Earth’s
interior
 Tells about
the makeup
and
structure of
earth
 Crust
 Mantle
• Lithosphere
• Mesosphere
• Asthenosphere
 core
• Inner
• outer
 What
causes the
speed of a seismic
wave to change???
 As
it passes through
Different layers of
Earth
 Area
where no
direct seismic
waves can be
detected
 Earthquakes
are the
result of stresses in
the lithosphere
 Most occur in 3 main
tectonic
environments
 Region
of
numerous
faults
 Faults zones
form at plate
boundaries
b/c of intense
stress as the
plates move
 New
Madrid,
Missouri
 1811
and 1812
 Felt
in South
Carolina
 Ancient
fault deep
in Earth
 Buried by
sediment
 Seismology-
study of
earthquakes and
seismic waves
 Seismograph-detects
and records
vibrations
 Vertical and
horizontal motions
recorded
 P-
waves
 S-waves
 Surface
waves
• Love
• Rayleigh
Arrive last
 Scientist
analyze the
arrival times of the p
& s waves
 A longer lag time
between p & s waves
means the further
away the EQ
occurred.
 Magnitude-
strength
of ground motion
 Richter
scale- gives a
strength reading
 Mercalli
scale- effects
of the earthquake
 The
movement of the
ground isn’t what
causes injury –it’s the
collapsing building
 Or
other dangers
• Fire
• Down electric & gas
• Explosion
• Landslides
• Etc.
 Earthquakes
that
occur in the water
may cause tsunamis
 If
you live in an area
where EQ’s occur you
should be prepared
 Areas
where few EQ’s
occur~ but have
occurred in the past
 Where EQ are likely
to occur in the future
 Small
earthquakes
that precede EQ
 Can
be minutes
before or weeks
 Looking
for signals
 Hoping
to detect EQ’s
early or before they
happen
 Water
in cracks
 Natural gas seepage
 Magnetic properties
 Scientists
keep
looking for ways to
improve
 May
2, 2015 in Battle
Creek
 March 2015 in
Portage
 Earthquakes
occur in Mi.
do