Earthquakes
What is an
earthquake?
What are
seismic waves?
 Earthquake= shaking ground
b/c plates rubbing against
e@other
 Sometimes destructive &
violent
 Happen along fault lines=
cracks in the crust where rocks
move
 Release of ++++ stored energy
when rocks break along a fault
 1000’s of EQ’s every day in the
world
 Can be too small to notice
 Focus= area beneath the
surface where EQ starts
 Epicenter= point on the surface
directly above the focus
(diagram)
 Seismic waves= energy from an
EQ going through Earth
 3 types of seismic wave:
Which
boundary has
the most intense
EQs?
1) P waves= (primary/pressure)
first wave, fastest moving,
moves like an accordionin/out/in/out
2) S waves= (secondary) next
wave, moves side to side
3) Surface waves= P+S waves @
the surface, slower than the
others; Rayleigh waves move
up/down + Love waves move
side to side= rolls like the
ocean
**From most to least intense**
1) Subduction zone EQ are deep
and INTENSE!!!!
2) Convergent c vs. c EQ are
deep and intense!!
3) Transform EQ are shallow
but can be intense-medium
quakes
4) Divergent EQ are shallow
and weak
 Intensity means how much
energy is released
 Amt of destruction & death
What are the
different kinds
of fault?
depends on location & intensity
 Big EQ where nobody lives =
no destruction, but big EQ in
populated place= lots of
destruction
 3 types of fault: (occur @ plate
boundaries)
1) Normal fault= tension stress
(pulling apart)
 Hanging wall slips down the
footwall
 “The footwall plants its foot
and stays put, the hanging wall
moves!”
(diagram)
2) Reverse Fault= compression
stress fault
 Hanging wall moves up &
over the foot wall
(diagram)
3) Strike-slip fault= shearing
stress (sliding stress)
 NO hanging wall or footwall
b/c they are on the same
plane
(diagram)
What are the
scales & tools
seismologists
use?
**EQs are
unpredictable…seismologists
know WHERE but can’t know
WHEN
SCALES TO MEASURE:
1) Mercalli Scale= measures
intensity of EQ @ a certain
spot from the epicenter
 Farther from the
epicenter/focus=weaker
intensity
 Measures destruction too
2) Richter Scale= measures the
magnitude of seismic waves
 Uses a seismograph=tool that
records seismic waves…creates
a seismogram=written record
of a EQ
 Diagram
 Good for small & near-by the
seismograph
3) Moment Magnitude Scale=
measures/estimates the total
energy released
 Combines data from
seismographs, how much
fault mvmt & strength of
rocks
 Best for ALL EQs
TOOLS to MONITOR:
1) Tiltmeter= measures vertical
mvmt on a reverse fault
2) Creep meter= measures
horizontal mvmt
3) Laser-ranging device=
measures horizontal mvmt
4) GPS= measures both
horizontal & vertical mvmt
 Determine the epicenter of an
EQ: use data from 3
seismographs--difference btwn
arrival of P waves and S waves
-- draw circles around the
seismograph location on a
map, where the lines cross is
the epicenter
(diagram)
How do EQs
cause death &
destruction?
 The difference btwn P wave &
S wave arrival time tells how
far away the seismograph is
from the epicenter…close
together= near the epicenter,
far apart= far from the
epicenter
 Use 3 seismographs & time
data to determine the exact
epicenter of an EQ
1) Liquefaction= loose, sandy
dirt turns into liquid mud
where there is a lot of ground
water during/after an EQ’s
shaking
 Buildings sink & collapse
2) Tsunami= a giant wave/wall
of water caused by an ocean
floor EQ
 Closer it gets to shore the
bigger it gets b/c the water is
shallower
 Tip of the nonsubducting
plate springs up, causing the
ocean to jerk forward
 600ish mph in deep water
 Tsunamis do not crest like an
ocean wave…hit the shore
like a battering ram!
3) Shaking= ground jerks
violently
 Produced by seismic
waves
 Causes landslides,
avalanches
 Causes building to fall
 Breaks water, gas &
electrical lines
 Different types of rock
determines how much the
ground shakes
4) Aftershock= a smaller EQ
after a bigger EQ in the same
area of the fault
 Happens b/c the fault is
settling back into locked
position
 Hours, days, months, yrs
after the big quake
 Weakened buildings fall
when the shake again
What is the
biggest EQ?
**amt of destruction & death
depends on how populated an area
is, magnitude of the EQ, quality of
buildings, & distance from the
epicenter b/c seismic waves lose
energy as they move away from
the epicenter
 Biggest magnitude:
1960 Chile 9.5
1964 Alaska 9.2
2004 Sumatra 9.0 (tsunami!)
2011 N. Japan 9.0 (tsunami!)
 Deadliest:
2010 Haiti (7.0)-222,570
2004 Sumatra (9.0)-227,898
2008 E. China (7.9)-87,578
2005 Pakistan (7.6)- 80,361
 Biggest EQ in CA: 1906 in San
Fransico (7.9)-3000 dead
 EQs shaking lasts ≈15seconds
to 5 minutes; avg≈1.5 minutes