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Earth
Science
Landforms
Earthquakes
Seismic Waves
Shadow Zone
Landforms
Mountains
• A mass of rock rising more than 600
meters above the surrounding land
• Relief vs. Elevation
Types of
Mountains
Fold Mountain
Fold Mountains
• Usually made mostly of
sedimentary rock folded by
compression forces
• These are the tallest and most
common of all mountains
Examples of
Fold Mountains
Appalachian Mountains
Rocky Mountains
Alps
Himalaya Mountains
Fault-Block Mountain
Fault Block Mountain
Ranges are cause by a
series of normal faults
Examples of
Fault block
Mountain ranges
Sierra Nevada Mountains, CA
Grand Tetons, WY
Wasatch Mountains, Utah
When the Earth SHAKES
Earthquakes
What causes
earthquakes?
• Volcanic eruptions can cause
earthquakes but most earthquakes
are caused by FAULTING
• These are often called TECTONIC
earthquakes
Theory VS. Law
• A THEORY is a logical idea that has
not been proven directly but it often can
be proved mathematically
• It is a working set of rules that define a
body of knowledge
• A LAW is observable and can be
proven- to a point. Nothing is 100%
sure in a Universe as vast as ours
Elastic Rebound Theory
The Elastic Rebound
Theory was first
proposed by American
geologist
Harry
Fielding Reid
after the 1906 San
Francisco Earthquake
Elastic Rebound
• The sudden release of
progressively stored strain in rocks,
resulting in movement along a fault
• After the stress becomes too great,
the rock layers break, vibrating
back and forth until eventually
coming to a rest
• As the rock layers are shaking back
and forth they send out waves of
vibration called Seismic Waves
• “Seismic” always has to do with
earthquake activity
Seismic Waves are waves
of vibration sent out in all
directions from the FOCUS
• Focus
The point below the surface where
the rock layers break and move
• Epicenter
The point on the surface, directly
above the focus. Where the greatest
damage usually occurs
Epicenter
Fault
Focus
Seismic Waves
Measuring
Earthquakes
Charles
Richter
26 April 1900 –
September 1985
30
Seismograph
A machine that measures earthquake
(seismic) waves
Zhang Heng
seismograph
is almost
2000 yrs old
Early Seismograph
Operates on the principle of
Newton’s First Law
Seismogram
The recorded information of earthquake
waves
Seismogram
The Richter Scale is based on
MAGNITUDE
Magnitude 1
Magnitude 2
Magnitude 3
Each # is TEN TIMES larger
than the # before it…
Pennies as an example:
Mag. 1 = 1 penny
Mag. 2 = 10 pennies
Mag 3 = 100 pennies
Mag. 4 = 1000 pennies
Mag. 5 = 10,000 pennies
Mag. 6 = 100,000 pennies
Mag. 7 = 1,000,000 pennies
Mag. 8 = 10,000,000 pennies
Mag. 9 = 100,000,000 pennies
Mag. 10 = 1,000,000,000 pennies
(that’s $10 million in pennies!!)
Richter Magnitudes
Earthquake Effects
Less than 3.5
3.5-5.4
Under 6.0
Generally not felt
Often felt, little damage
Slight damage to
buildings
Destructive to about 100
km from epicenter
Major earthquake. Can
cause serious damage
Large earthquake.
Serious damage for
hundreds of km
6.1-6.9
7.0-7.9
8 or greater
Anatomy
of
a
basic wave
• Crest – the highest point on a wave (A, F)
• Trough – the lowest point on a wave (D, I)
• Amplitude – the distance between the midpoint
& crest or trough
• Wavelength – distance between any two
successive points on a wave
• Frequency - # of vibrations/ second (Hertz)
Types of
Seismic Waves
Body Waves are
waves that travel
through the body
of the earth
Surface waves
only travel along
the surface of
earth
Body Waves
Primary Waves
AKA P-Wave
• Type of Longitudinal Wave
• Causes back and forth motion
• Follows the same direction as the
energy transfer
P-Waves
• Type of COMPRESSIONAL wave (like
sound)
• Will travel through solid, liquid or gas
• Travels at:
• 7.8 – 8.5 kps in mantle
• 7.2 kps in oceanic crust
• 3.5 kps in continental crust
Primary Wave
•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf
Secondary Wave
AKA S-Wave
• Particle motion is perpendicular to
direction of energy transfer
• Transverse or Shear Wave
• Will travel only through solids
• Travels 4 – 5 kps
Secondary Wave
•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf
Surface Waves
•
•
•
•
Two main types of surface waves:
Love Wave
Rayleigh Wave
Recent evidence show s that L-Waves
attenuate (gradually disappear) more
slowly in older rock (eastern US) and
more quickly in younger rock (western
US)
Love Wave
•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf
Love Waves
• Love Waves travel less than 4 kps
• Move side-to-side; like a snake
• Cause the most damage
Seismic Waves
Seismogram with the PWave, S-Wave and L-Wave
Seismic Risk in the US
Triangulation
Refraction
Refraction of seismic
waves within the Earth
Zone between about
105 degrees & 145 degrees
is the Shadow Zone
Focus
105 degrees
145 degrees
Shadow Zone
How Hawaiian Islands are formed