Regents Earth Science With Ms. Connery … they help tell Earth’s story!
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Regents Earth Science
With Ms. Connery
… they help tell Earth’s story!
EARTHQUAKE VOCABULARYearthquake
fault
convergent
divergent
transform (or
transverse)
seismic energy
epicenter
focus
Richter scale
magnitude
Mercalli scale
seismic risk
surface waves
body waves
p-waves
compression
s-waves
shear
s-wave shadow
zone
travel time
arrival time
origin time
mantle
convection
plate tectonics
plate
boundaries
earthquake
prediction
What DOES an EARTH“quake” look likE?
But the local quake MAY NOT BE the only
problem!
WHY IS IT IMPORTANT TO UNDERSTAND EARTHQUAKES?
Do you think we can predict them?
Where are the volcanoes and
quakes happening today???
Volcanoes
Remember, the
EVIDENCE –
LOCATIONS OF
VOLCANOES AND
EARTHQUAKES -
CAME FIRST
before plate
boundaries could
be drawn!
Quakes, MOUNTAIN chains, AND VOLCANOES ARE ALL RELATED!
IT’S ALL ABOUT earth’s CRUST in
MOTION – PLATE TECTONICS!!!
Here’s how scientists explain the relationship you observedIts all about convection in the asthenosphere(plastic mantle) & earthquake seismic waves prove it!
How does a lava lamp help us understand plate motion?
How does Mantle convection cause plate motion?
Mantle convection causes plate motion!
plate motion & volcanoes cause stresses to build up in
the rocks.
When the stresses overcome friction, movement OCCURS and causes an earthquake!
Its all about convection in the asthenosphere(plastic mantle) & earthquake seismic waves prove it!
What is an Earthquake?
BeforeAfter
< 1 Sec
It’s the SEISMIC
ENERGY that’s
released when the
earth “breaks”
along a fault zone
How do we describe where an earthquake occurs In
the lithosphere?
Focus is on the
fault zone where
the earthquake
occurred below
ground
How do we describe where an earthquake occurs In
the lithosphere?Epicenter is the
surface location used to
describe where it
happened using latitude
and longitude.
Be sure you know
the difference!
Focus
Earthquakes happen along faults
Generally they occur
from three types of
fault movement
caused by:
pulling (extension)
pushing
(compression)
sliding of the fault
blocks (lateral)
Divergence (slip fault)
Convergence (thrust fault)
Transverse (transform fault)
What is an earthquake?
• The fault locations are
somewhat predictable
• BUT exactly where &
when an earthquake will
occur its magnitude are
all unpredictable!
• Just like a pencil!
L – o - n - g - e - rthe distance moved
along the fault
the bigger the
earthquake!
Scales used to describe earthquakes
1. Richter “Magnitude” Scale
• Based on energy released
• Magnitude = X10 for each step
• Energy released about 30x
greater each step
RICHTER SCALE
Scales used to describe earthquakes
1. Richter “Magnitude” Scale
2. Mercalli Intensity Scale of
“Effects”
• Damage done based on costs
• Useful for insurance
USGS Map of Us seismic risks
earthquakes
An earthquake happens
when the forces that hold
the crust (rock) together
are not as strong as the
forces trying to tear it apartJust like a pencil!
– When friction “loses” the battle,
movement occurs along the fault
zone
– Seismic energy is released in
waves in 3-D (all directions) when
the earthquake happens
Seismic energy is released in waves
travelling in all directions (3D)
The seismic waves are called:
– Body waves (underground)
• primary seismic waves (p-waves)
• secondary seismic waves (s-waves)
– surface waves (above ground)
Draw isochron maps to see EVIDENCE
that shows p-waves differ from s-waves
What are the characteristics of the
p and s seismic waves that give them different speeds?
It’s slinky science time!
P-waves
Primary = p-waves
Compressional waves - similar to the motion of a slinky.
Particles move in same direction as energy wave travels
p-waves are fast (4-7 km/sec)
High density material fast wave speed
p-waves move through solid, liquid, & gas
S-waves
Secondary = s-waves
Shear (transverse) waves – think rope
Particles move perpendicular to the direction the
energy wave is traveling
S-waves slower than p-waves (2-5 km/sec)
High density material faster wave speed
Only travel through solids (can’t shear liquid or gas)
• EQKE Recording instruments are called
SEISMOGRAPHS (aka SEISMOMETERS)
• “Written” record of an earthquake is called a
SEISMOGRAM
How do we know the
properties of Earth’s
layers?
Seismic refraction and reflection of waves show us earth has layers with different properties!
Seismic Waves!!http://www.astro.virginia.edu/class/oconnell/astr121/im/seismic-waves-crossec-CM.jpg
http://www.visionlearning.com/library/module_viewer.php?mid=69
… since s-waves don’t make it through to the other side of Earth (shadow zone) so there
must be a liquid outer core that stops them!
Seismogram shows WHEN the SEISMIC waves
arrive at a station!
EARTHQUAKE
HAPPENS and
energy waves
are released
EARTHQUAKE
HAPPENS and
energy waves
are released
Faster P-wave arrives at
the seismograph FIRST
P-WAVE
ARRIVAL TIME
Slower s-wave arrives at
the seimograph LATER
S-WAVE
ARRIVAL TIME
EARTHQUAKE
HAPPENS and
energy waves
are released
P-WAVE
ARRIVAL TIME
S-WAVE
ARRIVAL TIME
http://eqseis.geosc.psu.edu/~cammon/QA/wellsNV-21Feb2008.html
P and s waves take different
amounts of time to travel the same distance away from an
equake because they move in
different ways
PRACTICE KEEPing UPWITH THE “times” !
TRAVEL TIME (how long it took waves to get there)
ARRIVAL TIME(when waves arrive at a seismograph)
ORIGIN TIME(earthquake happens)
00:00:00
What is a seismogram?
EARTHQUAKE
(energy waves
are released)
Earthquake
happens at the
TIME of ORIGIN and waves travel
out FROM FOCUS
Faster P-wave
arrives at the
seismograph FIRST
P-WAVE
ARRIVAL TIME
Slower s-wave arrives at
the seimograph LATER
S-WAVE
ARRIVAL TIME
Time gap
btw p
and s
What is the scale
for travel time?
What is the
scale for
epicenter
distance?
Label the faster
wave graph
Label the slower
wave graph
1 min = 60 sec
60sec/3 = ???
20 sec/ block
00:05:20
x axis = how far away
the seismograph is from
the earthquake
y axis = how long it took for
the seismic waves to travel
to the seismograph
Why does
the time gap
btw. arrival
of p & s
waves
change?
Practice using the esrt!!
What is a seismogram?
EARTHQUAKE
(energy waves
are released)
Earthquake
happens at the
TIME of ORIGIN and waves travel
out FROM FOCUS
Faster P-wave
arrives at the
seismograph FIRST
P-WAVE
ARRIVAL TIME
Slower s-wave arrives at
the seimograph LATER
S-WAVE
ARRIVAL TIME
Time gap
btw p
and s
If you know
difference in
arrival times, you
can figure out
how far away the
earthquake is!
TAKE A PIECE OF PAPER, AND MARK
OFF THE DIFFERENCE IN ARRIVAL TIME
if gap in time = 04:10
MOVE THE PAPER UNTIL THE TWO
TICK MARKS LINE UP WITH THE P
AND S CURVES
WHEN TICK MARKS LINE UP, GO
STRAIGHT DOWN AND READ THE
EPICENTER DISTANCE
EPICENTER DISTANCE
OF 2800 KM
EPICENTER DISTANCE
OF 2800 KM
If the EPICENTER
DISTANCE is 2800 km
from the seismograph,
how long did it take for
the p and s waves to
travel to the station
(TRAVEL TIME)?
EPICENTER DISTANCE
OF 2800 KM
If the p wave
arrived at the
station at 16:00:10,
what was the origin
time of the
earthquake?
NOW LET’s locate some earthquakes by
interpreting seismograms
What’s triangulation?
TRIANGLE THREE STATIONS!!!!!
Label the
closest
station
Label the
farthest
station
Determine the
epicenter distance
from each city
Use the data from the recording stations:
• Station A: San Francisco, California
P-Wave arrival S-Wave arrival
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording stations:
• Station B: Denver, Colorado
P-Wave arrival S-Wave arrival
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording stations:
• Station C: Missoula, Montana
P-Wave arrival S-Wave arrival
What is the time
difference
between P and
S wave arrivals?
03:01:00 03:03:00
Difference in arrival times:
San Francisco: 4:10
Denver, Colorado: 3:20
Missoula, Montana: 2:00
1. USE A PIECE OF PAPER TO MARK
OFF THE TIME GAP for that STATION
2. MOVE THE PAPER UNTIL THE
TWO TICK MARKS LINE UP WITH
THE P AND S GRAPHS
3. WHEN TICK MARKS LINE UP,
GO STRAIGHT DOWN AND
READ THE EPICENTER
DISTANCE
4. EPICENTER DISTANCE
OF 2800 KM
EPICENTER DISTANCES
San Francisco: 4:10
Denver, Colorado: 3:20
Missoula, Montana 2:00
2,800 km
1100 km
2,000 km
Where’s the earthquake???
San Francisco: travel time of 4:10
… is 2,800 km away
from earthquake
1,0
00
2,0
00
3,0
00
4,0
00
5,0
00
Open your compass to
the EXACT distance on
the scale.
Once you know distance, you can draw a circle
on the map that shows the possibilities!
. .
.
. .
.
Radius from SanFran =
2800 km
Radius from
Denver = 2000 km
Radius from
Missoula = 1100 km
Review of steps to locate epicenter!!!
Find the difference in arrival times
between p and s waves
Use the ESRT y-axis scale to mark off
the time gap on scrap paper
Match the time gap to p and s waves
curves on ESRT to find distance from the
epicenter on x-axis
Use map scale + compass to draw
circle from seismic station on map
Remember – you need at least 3 seismic
stations to locate the epicenter!
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