Real- Time Earthquake Data
http://earthquake.usgs.gov/
EQs
EQ = Movement of E’s lithosphere that occurs when rocks in
the lithosphere suddenly shift, releasing stored energy.
EQs occur b/c stress forces of have exceeded the strength of
rock.
Stress builds when rocks along 2 sides of a fault snag and
lock (friction)
as stress builds – so does POTENTIAL ENERGY IN
ROCKS
When rocks are strained beyond limit – they break & move.
(Potential  Kinetic Energy in form of seismic waves)
Elastic
Rebound
Tendency for
deformed rock
along a fault to
spring back to
original shape.
Stretched/strained
rock store
“elastic” or
potential energy
Stress & Strain on Rocks
Stress – Force that squeezes rocks
together, pulls them apart, pushes in diff.
directions.
Stress causes strain or deformation
(change in shape or volume) of rock
Stress
Does not exceed rock
strength
Folds
Exceeds rock strength
Faults
Stress
Does not exceed rock
strength
Folds = Bending rock
layers
High Temps. & Pressure
(deeper in crust)
Exceeds rock strength
Faults = Breaks in rock
layers & movement
along breaks
Low Temp. &
Pressure – Near Crust
Folds
Anticline = up facing fold
Syncline = down ward facing fold
Faults
Types of Faults
1. Dip – Slip
Motion up or down fault
surface
a. Reverse or Thrust:
Hanging wall moves UP.
b. Normal: Hanging wall
moves DOWN
http://www.windows.ucar.edu/tour/link=/earth/geology/fault.html
Types of Faults
2. Strike – slip
Sliding – Horizontal
Movement
3. Oblique – slip
dip-slip & strike slip
combined
Plate
Boundary:
Interpretation of Tectonic History
Convergent
Thrust/Reverse
Divergent
Normal
Transform
Strike-Slip
EQ Vibrations
•EQ vibrations begin at a
point called a FOCUS.
•Vibrations travel from focus
through the earth’s crust as
waves.
•Surface directly above the
focus is called the epicenter.
•These waves can be
detected and measured on
earth’s surface with a
SEISMOGRAPH.
SEISMOGRAPHS
Instrument that
measures &
records EQ
waves.
Strength of EQ
waves is
referred to as
MAGNITUDE.
Wave Motion:
http://aspire.cosmic-ray.org/Labs/SeismicWaves/
3 Types of Seismic Waves
1. Primary Waves (P waves)
2. Secondary Waves (S waves)
3. Surface Waves
Each wave originates from the FOCUS of
the earthquake.
Each wave travels in a different way, at
different speeds, and causes different
amounts of destruction.
Seismic Waves = vibrations produced by energy
released during EQ
P Waves: Primary Wave
•Arrives 1st & Travels
FASTER.
•Compress & Expand like
accordion (like sound
waves) Push/Pull waves
•Move through Solids &
Liquids
•Least destructive
Virtual EQs http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html
Seismic Waves http://www.geo.mtu.edu/UPSeis/waves.html
Seismic Waves
S Waves – Secondary
• What you FEEL in
an EQ
• Rock moves up &
down or side to side
(Snake-like)
• Arrive after P
• Move only through
SOLIDS
Seismic Waves: Surface
Waves
• Surface Waves develop when vibrations reach
surface
• Slowest waves
• Most destructive, most damaging
•
More P & S wave animations: http://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htm
•
Video clip: http://news.bbc.co.uk/1/hi/sci/tech/4126809.stm
Foreshocks Small Eqs that
may precede
major EQ
Aftershocks –
Eqs after major
EQ
(hours/weeks);
not all elastic
energy is
released
Rating Earthquakes
Earthquakes are rated in terms of
MAGNITUDE or INTENSITY by different
scales.
1. Moment Magnitude Scale
2. Richter Scale
3. Mercalli Scale
Moment Magnitude Scale
• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of ENERGY
• Each # releases ~32 times more ENERGY than
the # before it.
Example
A 6 releases 31 times more energy than a 5, and a 5 releases 31
times more energy than a 4. The energy difference between a 4
and a 6 EQ is 31 X 31 = 961
Richter Scale
• Uses a seismogram
• Rates on scale from 1- 10
• Looks at Eqs in terms of the SIZE OF THE
WAVES
• Each # has waves 10x bigger than previous #
1 – 3: Small earthquake waves – very little shaking
4 – 6: Moderate earthquakes – noticeable shaking and some damage
7 - 10+ BIG Earthquakes – Very destructive
Mercali Intensity Scale
•Measures observed RESULTS or
DAMAGE of Earthquake on a 1 – 12
scale
•Degree of shaking and DAMAGE to
structures
•Don’t need a seismogram
Link
•http://www.abag.ca.gov/bayarea/eqmaps/doc/mmi.html
1. Seismic Shaking –
ground vibrations
caused by seismic
waves. Can cause …
building collapse,
gas/water pipes to
burst, fires
EQ Hazards
Amount of shaking
depends on magnitude
& type of rock/soil
2. Liquefaction - water-logged soil can behave
as a liquid when seismic waves interact with;
building/bridge collapses
EQ Hazards
3. Landslides/ Mudflows –
loose soil/rock moves
downhill
4. Tsunamis:; caused by water
displacement due to EQ at sea
(usu. Subduction);
Starts as a 1m high wave in open
ocean; wave grows as it slows
and enters shallow coastal waters
http://news.bbc.co.uk/2/hi/science/
nature/7533972.stm
Seismic Waves are used to Study
Earth’s Interior
P and S waves are
“bent” and their
velocities are
affected as they
move through
material of varying
density
Link:
http://sunshine.chpc.utah.edu/labs/seismic/index.htm?ASPIRE_Sessi
on=964f1ed30b7e49ceb81bd77f444d9230
Latest Quakes
http://earthquake.usgs.gov/eqcenter/recente
qsww/Quakes/quakes_all.php
Top Ten Lists
http://earthquake.usgs.gov/eqcenter/top10.p
hp
Links
Virtual Earthquakes
http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.
html
Wave Types http://www.geo.mtu.edu/UPSeis/waves.html
Triangulation & “Hearing EQs”
http://www.seismo.unr.edu/ftp/pub/louie/class/100/seismic-waves.html
More virtual seismograms
http://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htm
Earthquakes outline subducting slab – Interactive Web Lab
http://openlearn.open.ac.uk/mod/resource/view.php?id=172185
CH. 22.5 OUTLINE QUIZ
1.Contrast a focus and an epicenter.
2.Name 3 types of seismic waves.
Provide a description for each.
3. Name 2 scales that evaluate or
measure Eqs. How are these scales
different from one another?
4. What is the relationship b/w Eqs and
plate boundaries?