EARTHQUAKES…
What is an Earthquake?
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Shaking and vibration at the surface of the earth caused
by the underground movement along a FAULT plane.
Results from a sudden release of energy in the Earth's
crust that creates SEISMIC WAVES.
Tectonic plate interaction is the primary cause.
1960 Valdivia Chile Earthquake
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Largest Earthquake ever recorded
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Moment Magnitude of 9.5!!!
This Building Was
Washed in by
Tsunami Wave
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Generated a massive tsunami
2000 killed – over $550M in damage
Ocean-Continental Convergence = Nazca Plate subducting
beneath S. American Plate
122 Killed in Onagawa, Japan
61 Killed Hilo, Hawaii
NAZCA PLATE
S. AMERICAN PLATE
EPICENTER
TRENCH
EPICENTER
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The location on Earth’s surface that lies directly
above the forces of an earthquake (The Focus).
FOCUS
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The zone within Earth where movement along
a fault produces an earthquake.
What is a FAULT?
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A FAULT is a fracture or zone of fractures
between two blocks of rock.
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Faults allow the blocks to move relative to each
other.
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Slow movement = “creep”
Rapid Movement = “earthquake”
Faults may range in length from a few
millimeters to thousands of kilometers.
3 Classifications of Faults
1. Normal Faults:
Rock above the fault plane has
moved DOWN relative to the rock below. (Divergence)
Normal Fault Flash Animation
2. Reverse (Thrust) Faults:
Rock above the
fault plane moves UP relative to the rock below.
(Convergence)
Thrust Fault Flash Animation
3. Strike-Slip Faults:
A fault along which the
movement is horizontal. (Transform)
Strike-slip Fault Flash Animation
Stress = Deformation
Sumatra Mega-thrust
(Reverse) Fault
Tsunami 2004, Dec. 26th
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http://www.news.cornell.edu/releases/Jan
05/tsunamiVid640.html
SUMATRA TSUNAMI 2004
Sumatra Tsunami 2004
So….
How do Seismologists measure the
strength of an
EARTHQUAKE?
Giuseppe Mercalli – 1902
Charles Richter – 1936
Qualitative Data
Quantitative Data
Modified Mercalli Scale (Qualitative)
Mercalli
Intensity
(at epicenter)
Witness Observations
I
Felt by very few people; barely noticeable.
II
Felt by a few people, especially on upper floors.
III
Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake.
IV
Felt by many indoors, few outdoors. May feel like heavy truck passing by.
V
Felt by almost everyone, some people awakened. Small objects moved. Trees and poles may
shake.
VI
Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys
may be slightly damaged.
VII
Slight to moderate damage in well built, ordinary structures. Considerable damage to poorly built
structures. Some walls may fall.
VIII
Little damage in specially built structures. Considerable damage to ordinary buildings, severe
damage to poorly built structures. Some walls collapse.
IX
Considerable damage to specially built structures, buildings shifted off foundations. Ground
cracked noticeably. Wholesale destruction. Landslides.
X
Most masonry and frame structures and their foundations destroyed. Ground badly cracked.
Landslides. Wholesale destruction.
XI
Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves
seen on ground.
XII
Total damage. Waves seen on ground. Objects thrown up into air.
Richter Scale is Logarithmic:
Each magnitude is 10x stronger than the previous.
MOMENT MAGNITUDE
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Invented in 1977 by Hiroo Kanamori
Moment is a measure of earthquake size that
takes into account how much the fault slips and
over how much area.
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Identical to Richter for EQ’s 7 and smaller.
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More precise for measuring larger EQ’s.
INTENSITY vs. MAGNITUDE
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The MAGNITUDE of an EQ is how much energy is
released during the event.
INTENSITY describes the perceptible moving,
shaking and damage experienced during the event.
Two EQ’s can have same magnitude, but very
different intensity depending upon such variables as
location relative to the epicenter, type of bedrock
and soil in the region, as well as the type of fault
where the EQ occurred.
How are Earthquakes Recorded?
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A seismogram is a record written by a seismograph in
response to ground motions produced by an earthquake,
explosion, or other ground-motion sources
How do Seismologists use this
Data?
Seismic Waves
1) Surface Waves: Waves that travel along
Earth’s outer layer.
2) Body Waves: Travel through Earth’s
Interior…….2 Kinds
P- Waves
S-Waves
***Identified by how they travel through the materials within the
Earth
Surface Waves
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Love Waves
The first kind of surface wave is called a Love wave,
named after A.E.H. Love, a British mathematician who
worked out the mathematical model for this kind of
wave in 1911. It's the fastest surface wave and moves
the ground from side-to-side.
Surface Waves
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Rayleigh Waves
The other kind of surface wave is the Rayleigh wave, named for
John William Strutt, Lord Rayleigh, who mathematically predicted
the existence of this kind of wave in 1885. A Rayleigh wave rolls
along the ground just like a wave rolls across a lake or an ocean.
Because it rolls, it moves the ground up and down, and side-to-side
in the same direction that the wave is moving. Most of the shaking
felt from an earthquake is due to the Rayleigh wave, which can be
much larger than the other waves.
P-Waves (Compression)
S-Waves (Shear)
P-Waves
S-Waves
Primary Waves
Secondary Waves
Faster
Slower
Compression “Push” Wave
“Shear” Waves
Direction of Particle Movement
(Push/Pull)
Direction of Particle Movement
(Side to Side)
Moves through liquids and
solids
Stop when they reach a
liquid medium
P Wave Shadow Zone
S Wave Shadow Zone
ESRT Time/Travel Graph P and S Waves
Sample Regents Problem
ESRT Time/Travel Graph
S - P = Lag Time (3 min.)
Calculate Distance from Seismic Station to Epicenter of EQ
Using ESRT
Let’s try it another way…
ESRT Time/Travel Graph
P and S Waves
7 min
Here’s Another One…
8/07 test
Take difference
between P arrival
and S arrival
And…..
Let’s Be Virtual Seismologists!
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Virtual Earthquake - An Introduction