Earthquakes
What is an
earthquake?
What are the
types of
seismic wave?
 Earthquake= ground shaking as
the result of plates sliding &
colliding w/e@other
 Fault lines= cracks in the Earth’s
surface where rocks slide against
e@ other
 Release ++++ stored energy from
rocks locked together @ a fault
line
 Focus= the exact spot where rock
breaks causing an
EQ…underground
 Epicenter= spot on the surface
above the focus
(diagram)
 Seismic wave= energy wave of an
EQ
 3 types of seismic wave:
1) P wave= first wave of energy
released (primary/pressure);
fastest waves move like an
accordion-in/out/in/outcompress/expand/compress/exp
and
2) S wave= after P waves
(secondary); side to side mvmt
3) Surface waves= P&S waves @
the epicenter out; roll like the
ocean…Rayleigh waves move
up and down & Love waves
move side to side
Which
*from strongest to weakest*
boundary has 1) convergent-subduction are deep
the most
and INTENSE!!!
intense EQs? 2) convergent- mtn building are deep
and intense!!
3) transform are shallow but can be
intense-medium intensity
4) divergent are shallow and weak
What are the
 3 types of fault:
different types 1) Normal fault= tension stress
of faults?
fault (pulling apart)
 Hanging wall goes down the
footwall
 “Footwall plants it foot and stays
put! Hanging wall moves!”
2) Reverse fault= compression
stress fault (pushing together)
 Hanging wall moves up &
over the footwall
3) Strike-slip fault= shearing
stress fault (grating against e@
other…cheese grater)
 NO hanging or footwall b/c
it doesn’t fall…it slides!
(diagrams)
How do
seismologists
measure and
monitor
EQ’s?
 EQs are
unpredictable…can’t
predict WHEN, but can
predict WHERE
SCALES to MEASURE:
1) Mercalli Scale= intensity @ a
given place based on distance
from the epicenter
 Seismic waves get weaker
and weaker the farther
away they go from the
epicenter/focus
 Less damage farther away
from the focus/epicenter
2) Richter Scale= magnitude of
the seismic wave
 Good for small & close-by
EQ
 Uses seismograph to
measure wave
magnitude…produces a
seismogram=written record
of the EQ
 (diagram)
3) Moment Magnitude Scale=
rates the total energy released
 Combines data from
seismographs, how much
mvmt and strength of rocks
that broke in the fault
 Rates ALL EQs
** regardless of the scale, the higher
#’s mean more intense EQ!**
** each magnitude level is 10x
energy/pwrful than the one before it
TOOLS to MONITOR
1) Creep meter for horizontal
mvmt
2) Tilt meter for up or down
(vertical) mvmt
3) Laser-ranging device for
horizontal mvmt
4) GPS for horizontal & vertical
mvmt
 Find the epicenter by comparing
the difference btwn p-wave & swave arrival at 3 seismographs.
-the time difference = how far
away the epicenter is from the
seismograph
-draw 3 circles & where they
cross is the epicenter
How do EQs
cause death
and
destruction?
(diagram)
1) Shaking ground will knock
down buildings not built right
 Can fracture gas, water lines
 Knock down power poles which
could start fires
 Could start a landslide/avalanche
 Soft/loose soil shakes more than
solid rock so stuff built on
soft/loose soil is damaged easier
 Buildings fall & people die
2) Liquefaction= water rising b/c
of an earthquake’s shaking
turning soft, loose soil into
mud.
 Buildings sink into the mud,
like quicksand
 ex: like swishing wet sand
with your hand @ the
beach
3) Tsunami= an ocean wave that
gets bigger when it reaches
shallow water
 Caused by an epicenter on
the ocean floor @ a
subduction zone
 Flick of the nonsubducting
plate’s edge causes the
tsunami
 Move as fast as a fighter
jet…600ish mph
 Do not crest like a regular
wave
 Are like a battering ram
instead
4) Aftershock= a smaller EQ after
a lrg EQ in the same place on
the fault
 b/c of the fault settling back
into its locked position
 can happen hours, days,
months or even yrs after the
lrg EQ
 can destroy weakened
buildings
**amt of death & destruction is
determined where civilization is,
magnitude of the EQ, building
quality (well-built vs. poorly built),
& distance from the epicenter b/c
seismic waves lose energy the farther
they go from the epicenter
When and
 most intense/biggest magnitude:
where was the
1960 in Chile-9.5
largest EQ?
1964 in Alaska-9.2
2004 in I. Ocean (Sumatra
tsunami)-9.0
2011 in N. Japan (tsunami)-9.0
 biggest death toll
2010 in Haiti (7.0)=222,570
2004 in I. Ocean (9.0)=227,898
2008 in China (7.9)=80, 587
2005 in Pakistan (7.6)=80,361
 biggest EQ in CA: 1906 San
Fransico (7.9)=3000